1000 Sentences With "sexual reproduction" | Random Sentence Generator

ANTAGONISM is built into the nature of sexual reproduction itself.

Also, sexual reproduction introduces new genetic variation within a species.

Nobody has previously demonstrated successful sexual reproduction for offspring produced through facultative parthenogenesis.

And it must have the craziest sexual reproduction strategy in the entire plant world.

Among population geneticists, sexual reproduction is notoriously difficult to justify as an evolutionary strategy.

Evolutionary biologists have long included microbes and parasites in how they think about sexual reproduction.

Although domestication led sexual reproduction to decay, traits useful for life in a brewery became more common.

Sexual reproduction outside their native habitat is restricted to individuals occupying outdoor situations in tropical or subtropical climates.

Jeffrey Epstein, wearing glasses to the right, seated next to Nicholas Pritzker, laughs at Martin Nowak's comment about sexual reproduction.

Would she ever again hear Anahah's laughter over the improbable genesis of multicellular biologic life through the sexual reproduction of slime molds?

Sexual reproduction shuffles up an organism's DNA - the building blocks of life - creating genetic diversity and eliminating undesirable mutations, helping a species survive.

The advantage: Sexual reproduction in a species, cumulated over all its members, stirs the species' gene pool, rebalancing the genes into different combinations.

GUILT-FREE intercourse may, as Philip Larkin wrote, have begun in 1963, but sexual reproduction has been around a good deal longer than that.

Six lines of each mating type were forced to undergo sexual reproduction every 90 generations, by mixing the sexes together and adding the antibiotics.

Honeysuckle is not solely dependent upon sexual reproduction, though; the aggressive vine reproduces vegetatively as well, easily rooting where its stems contact the ground.

Sexual reproduction seems an inferior strategy — only half of a parent's genes (the good and the bad) are passed on and it requires a mate.

Germ-plasm is composed of our germ cells, which are involved in sexual reproduction and contain the genes that are passed down from previous generations.

But maybe Earth life would adapt to an alien ecosystem, Gatti told me, perhaps even sharing genes with it in a case of interstellar sexual reproduction.

Never mind that ovaries and testicles do have structural and functional similarities—they provide genetic material for sexual reproduction in the form of eggs and sperm.

Gene drives are highly controversial: if they work, they could give humans the power to wipe out—with minimal effort—any species that engages in sexual reproduction.

Sexual reproduction shuffles genetic variants throughout the entire genome, providing an almost limitless variety for evolution to act upon, even with a limited number of individuals within a species.

It's even possible to combine algorithms in a parody of sexual reproduction, so that two good features, one from each of two different algorithms, can be united in one.

Without sexual reproduction — a grain of pollen fertilizing an egg, as occurs with most other fruit species — there's no random variation among plants that growers need to worry about.

"We were interested in the question of why mammals can only undergo sexual reproduction," Qi Zhou, a biologist at Chinese Academy of Sciences Institute of Zoology, said in a statement.

WASHINGTON (Reuters) - An all-female freshwater fish species called the Amazon molly that inhabits rivers and creeks along the Texas-Mexico border is living proof that sexual reproduction may be vastly over-rated.

He developed what has come to be known as the Mitochondrial Eve hypothesis by looking at a special type of DNA which is passed, unmixed by sexual reproduction, from a mother to her children.

Taking into account the wholesale reshuffling of genes that occurs in sexual reproduction would massively complicate the models, Nowak and Chatterjee said, and to their knowledge, no one has yet seriously taken on that challenge.

They could hide lots of different gene combinations in their complex genomes, so the result of mixing that genetic information up in sexual reproduction leads to offspring that are worse-off than their parents, according to one 2016 paper.

When it's broken and rejoined, as routinely happens when DNA is damaged but also during the recombination of genes in sexual reproduction, large numbers of transposons make it easy for strands to misalign, and that slippage can result in deletions.

Unlike earlier "coral gardening" efforts, in which fragments of adult coral are collected, spawned asexually in nurseries, and then returned to their reef, the focus of SECORE's effort has been on producing new genetic varieties of coral via sexual reproduction.

Instead of going backward to an earlier stage of humanity, these books push forward to a posthuman future in which human beings are replaced by a species that has abolished sexual reproduction, and so is immune to the torments of desire and loneliness.

That Homo sapiens began as an African species was pretty-much proved in the 1980s by Allan Wilson of the University of California, Berkeley, who looked at a special type of DNA which is passed, unmixed by sexual reproduction, from a mother to her children.

Short-lived species seem to be able to "trade in" their investment in growth and sexual reproduction in return for slowing down the ageing process -- switching to a physiological state in which they instead invest in maintenance of body condition and warding off senescence.

" Edward Vargo, an entomology professor at Texas A&M University who was not involved in the study, added that determining how and why certain colonies evolved asexuality might yield insight on the big question of "what is the purpose of sex and sexual reproduction.

Epstein was captured on video sitting next to Pritzker and laughing as Martin Nowak, who received $6.5 million from Epstein in 2003 to launch his Program for Evolutionary Dynamics at Harvard, explained how sexual reproduction generates "noise" in models of the evolution of cooperative behavior.

They found that the Amazon molly, named after the fierce female warriors of ancient Greek mythology, boasts a hardy genetic makeup that makes it equally fit, or even more so, than fish using sexual reproduction in which both maternal and paternal genes are passed along to offspring.

Many of Lysenko's views were either preposterous or simply irrelevant, and Ings includes a great scene when Western delegates to a conference in the Soviet Union burst into hysterics after hearing Lysenko's sophomoric theories on how sexual reproduction was a mixture of cells eating one another and belching.

Found in a type of fish called Squalius alburnoides, which normally inhabits rivers in Portugal or Spain, this is the first documented instance in vertebrates of a father producing a near clone of itself through sexual reproduction — a rare phenomenon called androgenesis — the researchers reported in the journal Royal Society Open Science on Wednesday.

The discovery of sexual reproduction in T. brucei supports the hypothesis that meiosis and sexual reproduction are ancestral and ubiquitous features of eukaryotes.

In fact, we tend to think of sexual reproduction and true multicellularity as occurring at the same time, and true multicellularity is often taken as a marker for sexual reproduction.

The fossil includes differentiated reproductive cells that are the oldest evidence of sexual reproduction. Sexual reproduction increased genetic variation, which led to an increased rate of evolution and the diversification of eukaryotes.

It may also undergo sexual reproduction by producing minute, microscopic flowers.

The first fossilized evidence of sexual reproduction in eukaryotes is from the Stenian period, about 1 to 1.2 billion years ago. Biologists studying evolution propose several explanations for the development of sexual reproduction and its maintenance. These reasons include reducing the likelihood of the accumulation of deleterious mutations, increasing rate of adaptation to changing environments, dealing with competition, DNA repair and masking deleterious mutations. All of these ideas about why sexual reproduction has been maintained are generally supported, but ultimately the size of the population determines if sexual reproduction is entirely beneficial.

Larger populations appear to respond more quickly to some of the benefits obtained through sexual reproduction than do smaller population sizes. Maintenance of sexual reproduction has been explained by theories that work at several levels of selection, though some of these models remain controversial. However, newer models presented in recent years suggest a basic advantage for sexual reproduction in slowly reproducing complex organisms. Sexual reproduction allows these species to exhibit characteristics that depend on the specific environment that they inhabit, and the particular survival strategies that they employ.

Although sexual reproduction in fungi varies between phyla, for some fungi the sporangium plays an indirect role in sexual reproduction. For Zygomycota, sexual reproduction occurs when the haploid hyphae from two individuals join to form a zygosporangium in response to unfavorable conditions. The haploid nuclei within the zygosporangium then fuse into diploid nuclei.When conditions improve the zygosporangium germinates, undergoes meiosis and produces a sporangium, which releases spores.

Puffballs emitting spores Fungi are classified by the methods of sexual reproduction they employ. The outcome of sexual reproduction most often is the production of resting spores that are used to survive inclement times and to spread. There are typically three phases in the sexual reproduction of fungi: plasmogamy, karyogamy and meiosis. The cytoplasm of two parent cells fuse during plasmogamy and the nuclei fuse during karyogamy.

That definition is not universally accepted. Osborn advocated for higher rates of sexual reproduction among people with desired traits ("positive eugenics") or reduced rates of sexual reproduction or sterilization of people with less-desired or undesired traits ("negative eugenics").

Nonflowering plants like ferns, moss and liverworts use other means of sexual reproduction.

When I speak of sexual reproduction in this essay, I mean anisogamous amphimixis.

The males of the species no longer produce viable sperm for sexual reproduction, and the females do not respond to any cues or advances by the males for sexual reproduction. Finally, the females lose a major muscle in their spermathecae that allow them to contain sperm after sexual reproduction. Therefore, without the symbiotic relationship between Wolbachia and M. uniraptor, the wasp species would not persist alone by means of sexual reproduction because of these evolutionary alterations that increase the fitness of the persisting relationship with the bacteria. The bacteria have seemingly inhibited the wasps' reproductive pathways through selective pressures to increase the fitness of their relationship, and the wasp is unlikely to regress to its former state of sexual reproduction as a result of these genetic alterations.

The paradox of the existence of sexual reproduction is that though it is ubiquitous in multicellular organisms, there are ostensibly many inherent disadvantages to reproducing sexually when weighed against the relative advantages of alternative forms of reproduction, such as asexual reproduction. Thus, because sexual reproduction abounds in complex multicellular life, there must be some significant benefit(s) to sex and sexual reproduction that compensates for these fundamental disadvantages.

Sexual Reproduction in Humans. 2006. John W. Kimball. Kimball's Biology Pages, and online textbook.

Lirapex costellatus form shallow marine sediments. It is a chemosymbiotroph. It has sexual reproduction.

The fully developed mature stage. As an adult, it is capable of sexual reproduction.

Sexual reproduction is also noted to occur within this genus, although it is rare.

It has already been understood that since sexual reproduction is not associated with any clear reproductive advantages, as compared with asexual, there should be some important advantages in evolution.Crow J.F. (1994). Advantages of Sexual Reproduction, Dev. Gen., vol.15, pp. 205-213.

Sexual reproduction occurs all year and it is assumed that the larvae are not pelagic.

Sexual reproduction is thought to happen afterwards in galls formed on the midvein of new leaves.

Each is different and found on a different chromosome excluding the possibility of homozygous sexual reproduction.

Stentor coeruleus are capable of sexual reproduction, or conjugation, but primarily reproduce asexually by binary fission.

However, the species can reproduce asexually in a wider range of temperatures than during sexual reproduction.

A comparison of the current understanding of sexual reproduction in ascomycete fungi to the brachymeiosis hypothesis.

It has already been stated that both parthenogenesis and gemmation are ultimately derived from sexual reproduction.

This diagram illustrates how sexual reproduction (top) might create new genotypes faster than asexual reproduction (bottom). The advantageous alleles A and B occur randomly. In sexual reproduction, the two alleles are combined rapidly. But in asexual reproduction, the two alleles must independently arise through clonal interference.

As in most cnidarians sexual reproduction is not an imperative way for cannonballs to reproduce. They can reproduce both sexually and asexually. During sexual reproduction, cannonballs shoot sperm out of their mouth. The sperm are then caught by another cannonball through the mouth and fertilization happens.

The journal of men's health & gender, 2(3), 339-345. Based on the pleasure model of sexual motivation, the increased sexual reproduction pleasure that occurs following oxytocin release may encourage motivation to engage in future sexual reproduction activities. Emotional closeness can be an especially strong predictor of sexual motivation in females and insufficient oxytocin release may subsequently diminish sexual reproduction arousal and motivation in females. High levels of vasopressin can lead to decreases in sexual motivation for females.

Canine reproduction is the process of sexual reproduction in domestic dogs, wolves, coyotes and other canine species.

Sexual reproduction is not known for all species of Saccharomycotina, but may happen in certain species if environmental conditions favour it (e.g. deficiency in nitrogen and carbohydrate). Sexual reproduction is well known in Saccharomyces cerevisiae. Here, the life cycle involves alternation between a haploid and a diploid phase.

In homothallic sexual reproduction, two haploid nuclei derived from the same individual fuse to form a zygote that can then undergo meiosis. Homothallic fungi include species with an aspergillus-like asexual stage (anamorphs) occurring in numerous different genera, several species of the ascomycete genus Cochliobolus, and the ascomycete Pneumocystis jiroveccii. Heitman reviewed evidence bearing on the evolution of sexual reproduction in the fungi and concluded that the earliest mode of sexual reproduction among eukaryotes was likely homothallism, that is, self-fertile unisexual reproduction.

Jellyfish exhibits both asexual and sexual reproduction by budding during hydroid stage and releasing gametes in medusae stages.

Alexey Simonovich Kondrashov () (born April 11, 1957) worked on a variety of subjects in evolutionary genetics. He is best known for the deterministic mutation hypothesisKondrashov, A.S. 1988. Deleterious mutations and the evolution of sexual reproduction. Nature 336: 435-440 explaining the maintenance of sexual reproduction,Kondrashov AS & Crow JF. 1991.

Penicillium chrysogenum is of major medical and historical importance as the original and present-day industrial source of the antibiotic penicillin. The species was considered asexual for more than 100 years despite concerted efforts to induce sexual reproduction. However, in 2013, Bohm et al. finally demonstrated sexual reproduction in P. chrysogenum.

121-130 a process that enables cells to correct mistakes in replicating DNA. Meselson's current research is aimed at understanding the advantage of sexual reproduction in evolution. Meselson and his colleagues have recently demonstrated that Bdelloid rotifers do, in fact, engage in sexual reproduction employing meiosis of an atypical sort.

Jakoba use asexual reproduction by binary fission. The sexual reproduction or the formation of cysts have not been observed.

A complete lack of sexual reproduction is relatively rare among multicellular organisms, particularly animals. It is not entirely understood why the ability to reproduce sexually is so common among them. Current hypotheses suggest that asexual reproduction may have short term benefits when rapid population growth is important or in stable environments, while sexual reproduction offers a net advantage by allowing more rapid generation of genetic diversity, allowing adaptation to changing environments. Developmental constraints may underlie why few animals have relinquished sexual reproduction completely in their life-cycles.

These individuals are called Zooids. These animals generally reproduce asexually by budding, though sexual reproduction does occur in some groups.

Synergistic epistasis is central to some theories of the purging of mutation load and to the evolution of sexual reproduction.

In another evolutionary study, introduction of partial CUG identity redefinition (from Candida species) into Saccharomyces cerevisiae clones caused a stress response that negatively affected sexual reproduction. This CUG identity redefinition, occurring in ancestors of Candida species, was thought to lock these species into a diploid or polyploid state with possible blockage of sexual reproduction.

No multiplication or sexual reproduction of microfilariae occurs in the mosquito. 8-1 The infective larvae (L3) migrate to the salivary glands, enter the proboscis and escape onto human skin when the mosquito takes another blood meal. Human: B. malayi undergoes further development in the human as well as sexual reproduction and egg production.

V. inaequalis overwinters mostly as immature Perithecia, where sexual reproduction takes place, producing a new generation of ascospores that are released the following spring. Scab lesions located on the woody tissues may also overwinter in place, but will not undergo a sexual reproduction cycle; these lesions can still produce ineffective conidial spores in the spring.

Genetic exchange has been identified among field populations of T. cruzi. This process appears to involve genetic recombination as well as a meiotic mechanism. Despite the capability for sexual reproduction, natural populations of T. cruzi exhibit clonal population structures. It appears that frequent sexual reproduction events occur primarily between close relatives resulting in an apparent clonal population structure.

Dermatophytes reproduce sexually by either of two modes, heterothallism or homothallism. In heterothallic species, interaction of two individuals with compatible mating types are required in order for sexual reproduction to occur. In contrast, homothallic fungi are self-fertile and can complete a sexual cycle without a partner of opposite mating type. Both types of sexual reproduction involve meiosis.

Clonal isolates have observed to produce both sperm and eggs. Two eggs are produced from each oogonium and 64 sperm are produced from each spermatogonangium. The frequency of sexual reproduction in D. brightwellii is not clear, although conditions including increased nutrients, temperatures ranging from 10 °C-14 °C, and a short photoperiod may be favorable for sexual reproduction.

The lower surface engulfs small particles of organic detritus, on which the animal feeds. It reproduces asexually, budding off smaller individuals, and the lower surface may also bud off eggs into the mesenchyme. Sexual reproduction has been reported to occur in one clade of the placozoa. Intergenic recombination was observed as well as other hallmarks of sexual reproduction.

This homologue is passed down across generations without having its mutations disrupted by recombination during sexual reproduction, allowing it to properly accumulate mutations.

The development of Theileria in ticks includes sexual reproduction which enables generation of new variants that can evade the immune mechanisms of cattle.

Unusual phenotypes can be preserved vegetatively. Sexual reproduction is via seed. The apomictic species freely set seed and faithfully reproduce the maternal phenotype.

Humans are the intermediate hosts in which asexual reproduction occurs, and female anopheline mosquitos are the definitive hosts harbouring the sexual reproduction stage.

The mutation is the ultimate source of genetic variation, but mechanisms such as sexual reproduction and genetic drift contribute to it as well.

Ladybugs mating Pollen production is an essential step in sexual reproduction of seed plants. The evolution of sexual reproduction is an adaptive feature which is common to almost all multi-cellular organisms (and also some single- cellular organisms) with many being incapable of reproducing asexually. Prior to the advent of sexual reproduction, the adaptation process whereby genes would change from one generation to the next (genetic mutation) happened very slowly and randomly. Sex evolved as an extremely efficient mechanism for producing variation, and this had the major advantage of enabling organisms to adapt to changing environments.

Diversification into the phylogenetic tree happens much more rapidly via sexual reproduction than it does by way of asexual reproduction. Evolution of sexual reproduction describes how sexually reproducing animals, plants, fungi and protists could have evolved from a common ancestor that was a single- celled eukaryotic species. m Sexual reproduction is widespread in the Eukarya, though a few eukaryotic species have secondarily lost the ability to reproduce sexually, such as Bdelloidea, and some plants and animals routinely reproduce asexually (by apomixis and parthenogenesis) without entirely having lost sex. The evolution of sex contains two related yet distinct themes: its origin and its maintenance.

The origin of sexual reproduction can be traced to early prokaryotes, around two billion years ago (Gya), when bacteria began exchanging genes via conjugation, transformation, and transduction. Though these processes are distinct from true sexual reproduction, they share some basic similarities. In eukaryotes, true sex is thought to have arisen in the Last Eukaryotic Common Ancestor (LECA), possibly via several processes of varying success, and then to have persisted (compare to "LUCA"). Since hypotheses for the origin of sex are difficult to verify experimentally (outside of evolutionary computation), most current work has focused on the persistence of sexual reproduction over evolutionary time.

The evolution of sexual reproduction is considered paradoxical, because asexual reproduction should be able to outperform it as every young organism created can bear its own young. This implies that an asexual population has an intrinsic capacity to grow more rapidly with each generation.John Maynard Smith The Evolution of Sex 1978. This 50% cost is a fitness disadvantage of sexual reproduction.

Reproduction refers to the process in which an offspring is formed via asexual reproduction or sexual reproduction. Asexual reproduction involves one parent, producing a genetically identical offspring, to the parent cell. Whereas sexual reproduction involves the meeting and fertilisation of gamete cells in order to produce a genetically different offspring. Fungi type organisms reproduce asexually through the release of diploid spores.

These hypothesis test for colouration due to thermoregulation, predator avoidance, and social cues, specifically sexual reproduction. Through an experiment conducted by Vercken et al., colour polymorphism in viviparous lizard is caused by social cues, rather than the other hypotheses. More specifically, the ventral colouration that is seen in female lizards is associated with patterns of sexual reproduction and sex allocation.

Alpine plants use both sexual reproduction and asexual reproduction. Sexual reproduction has limits in high alpine areas, especially in areas with a short growing season in alpine zones at high latitudes. In tropical alpine zones with a year-round growing season, such as the northern Andes, plants can flower year round. Regardless of when alpine plants flower, pollinators are often scarce.

The "Vicar of Bray" hypothesis (or Fisher-Muller Model ) attempts to explain why sexual reproduction might have advantages over asexual reproduction. Reproduction is the process by which organisms give rise to offspring. Asexual reproduction involves a single parent and results in offspring that are genetically identical to each other and to the parent. In contrast to asexual reproduction, sexual reproduction involves two parents.

Extensions called gametangia are formed from each of the compatible haploid mycelia. Following anastomosis, a fertile heterokaryotic zygosporangium is formed within which the zygospores develop. During sexual reproduction, carotenoid pigments are produced by both of mating type. Carotenoids are precursors of many apocarotenoids that contain very important sex-specific precursors, trisporic acid (TSA) for the sexual reproduction of Blakeslea trispora.

Homothallic reproduction is characterized by the fusion of the asexual oogonium and antheridium. This fusion leads to the formation and release of sexual oospores, the primary inoculum for the next season. Heterothallic sexual reproduction is the fusion of sexual cells from two separate organisms, leading to "outcrossing".Spring, O. (2000) Homothallic sexual reproduction in Plasmopara halstedii, the downy mildew of sunflower.

Once infection season comes to an end, sexual reproduction occurs to form an oospore. In order to have successful sexual reproduction, weather conditions must be favorable and mating types must match. Two mating types, A1 and A2, exist for Phytophthora colocasiae. Hormonal signaling allows for sporangia of the two mating types to come together and initiate the development of oogonia and antheridia.

The conidia will be dispersed by the wind is able to infect other plants. The asexual cycle only takes five to seven days to complete. Sexual reproduction occurs when the conditions are unfavourable and it needs to withstand harsh environmental conditions. During sexual reproduction, the hyphae will undergo meiosis forming antheridia and oogonia, the only haploid structures in the Peronospora life history.

A baby Komodo dragon, Varanus komodoensis, produced through parthenogenesis. Komodo dragons are an example of a species which can produce offspring both through sexual reproduction and parthenogenesis. Some species reproduce exclusively by parthenogenesis (such as the bdelloid rotifers), while others can switch between sexual reproduction and parthenogenesis. This is called facultative parthenogenesis (other terms are cyclical parthenogenesis, heterogamy or heterogony).

Although sexual reproduction was suspected, no evidence exists of it.Frenzel, J., 1892. "Untersuchungen über die mikroskopische Fauna Argentiniens." Archiv für Naturgeschichte, 58: 66–96.

Although sexual reproduction is unknown and cysts have not been found to date, they are able to reproduce asexually by means of binary fission.

Coccidiosis is also present in goats, and is the largest cause of diarrhea in young goats. It can also greatly affect sexual reproduction of goats.

Pseudo- nitzschia australis can reproduce both sexually and asexually by binary fission. Sexual reproduction occurs by auxo-sporulation in which gametes fuse to form a zygote. Sexual reproduction has also been found to correlate with higher levels of domoic acid production Population growth of this species is seasonal and can depend on the amount of water upwelled and nutrient concentrations present off of the coast.

Furthermore, direct evidence for meiotic recombination, indicative of mating and sexual reproduction, was also found in G. intestinalis. Other protists for which evidence of mating and sexual reproduction has recently been described are parasitic protozoa of the genus Leishmania, Trichomonas vaginalis, and acanthamoeba. Protists generally reproduce asexually under favorable environmental conditions, but tend to reproduce sexually under stressful conditions, such as starvation or heat shock.

Most commonly, Elkhorn coral reproduce asexually, their most common type of reproduction. During storms, strong waves, or ship disturbances, fragments of coral break off and are transported to other areas where new colonies can begin. The new colonies are genetically identical to their parent colonies, while sexual reproduction results in new genotypes. Also, as opposed to sexual reproduction, fragmentation can occur at any time of the year.

This is also true for fungi where the sexual phase is present, although in this case, additional and significant variation is incorporated through the sexual reproduction.

Tanja Schwander is a Swiss evolutionary biologist and professor at the University of Lausanne. She is known for her work on the Evolution of sexual reproduction.

Sexual reproduction and vegetative reproduction is common mean of reproduction in Pyrus pashia. Seed stored under refrigerated conditions will remain viable for 2 to 3 years.

Mann DG), pp. 33–46. Otto Koeltz-Science, Koenigstein. However, samples from Puget Sound, WA display high genetic diversity. This is indicative of sexual reproduction (auxospore formation).

The B. britannica hydroid buds and forms medusae by asexual reproduction. When these mature, sexual reproduction occurs, the fertilised eggs settle out and new hydroids are formed.

Sexual reproduction with meiosis has been directly observed in all fungal phyla except Glomeromycota (genetic analysis suggests meiosis in Glomeromycota as well). It differs in many aspects from sexual reproduction in animals or plants. Differences also exist between fungal groups and can be used to discriminate species by morphological differences in sexual structures and reproductive strategies. Mating experiments between fungal isolates may identify species on the basis of biological species concepts.

Most brown algae, with the exception of the Fucales, perform sexual reproduction through sporic meiosis. Between generations, the algae go through separate sporophyte (diploid) and gametophyte (haploid) phases. The sporophyte stage is often the more visible of the two, though some species of brown algae have similar diploid and haploid phases. Free floating forms of brown algae often do not undergo sexual reproduction until they attach themselves to substrate.

True multicellular organisms contain cells that are specialized for different functions. This is, in fact, an essential feature of sexual reproduction as well, since the male and female gametes are specialized cells. Organisms that reproduce sexually must solve the problem of generating an entire organism from just the germ cells. Sexual reproduction and the ability of gametes to develop into an organism are the necessary antecedents to true multicellularity.

Brewer RH. 1989. The Annual Pattern of Feeding, Growth, and Sexual Reproduction in Cyanea (Cnidaria: Scyphozoa) in the Niantic River Estuary, Connecticut. The Biological bulletin 176:272–281.

Sexual reproduction has been proposed to have evolved in both the Ascomycota and Basidiomycota as an adaptation for repair of DNA damage via homologous recombination under stressful conditions.

Hosts have evolved a variety of defensive measures against their parasites, including physical barriers like the skin of vertebrates, the immune system of mammals, insects actively removing parasites, and defensive chemicals in plants. The evolutionary biologist W. D. Hamilton suggested that sexual reproduction could have evolved to help to defeat multiple parasites by enabling genetic recombination, the shuffling of genes to create varied combinations. Hamilton showed by mathematical modelling that sexual reproduction would be evolutionarily stable in different situations, and that the theory's predictions matched the actual ecology of sexual reproduction. However, there may be a trade-off between immunocompetence and breeding male vertebrate hosts' secondary sex characteristics, such as the plumage of peacocks and the manes of lions.

Sex. This chapter is a discussion of theories of the evolution of sexual reproduction. The common-sense explanation is that although asexual reproduction is much easier and more efficient for an organism it is less common than sexual reproduction because having two parents allows species to adapt and evolve more easily to survive in changing environments. Brooks discusses efforts to prove this by laboratory experiment and goes on to discuss alternative theories including the work of Joan Roughgarden of Stanford University who proposes that sexual reproduction, rather than being driven by Charles Darwin's sexual selection in individuals, is a mechanism for the survival of social groupings, which most higher species depend on for survival.

Sponges are generally hermaphrodite; sexual reproduction is by the release of gametes into the water column; asexual reproduction may be by budding, or by detachment of fragments of sponge.

Each conidium is haploid and bears only one nucleus. Sexual reproduction in P. digitatum has not been observed. Penicillium digitatum can also grow on a variety of laboratory media.

While theories positing fitness benefits that led to the origin of sex are often problematic, several theories addressing the emergence of the mechanisms of sexual reproduction have been proposed.

Dinoflagellata life cycle: 1-mitosis, 2-sexual reproduction, 3-planozygote, 4-hypnozygote, 5-planomeiocyte Dinoflagellates have a haplontic life cycle, with the possible exception of Noctiluca and its relatives. The life cycle usually involves asexual reproduction by means of mitosis, either through desmoschisis or eleuteroschisis. More complex life cycles occur, more particularly with parasitic dinoflagellates. Sexual reproduction also occurs, though this mode of reproduction is only known in a small percentage of dinoflagellates.

A cladocera giving birth (100x magnification) With the exception of a few purely asexual species, the lifecycle of cladocerans is dominated by asexual reproduction, with occasional periods of sexual reproduction; this is known as cyclical parthenogenesis. The system evolved in the Permian, when the Cladocera arose. When conditions are favourable, reproduction occurs by parthenogenesis for several generations, producing only female clones. As the conditions deteriorate, males are produced, and sexual reproduction occurs.

Compsobuthus werneri female with young (white) A few arthropods, such as barnacles, are hermaphroditic, that is, each can have the organs of both sexes. However, individuals of most species remain of one sex their entire lives. A few species of insects and crustaceans can reproduce by parthenogenesis, especially if conditions favor a "population explosion". However, most arthropods rely on sexual reproduction, and parthenogenetic species often revert to sexual reproduction when conditions become less favorable.

Animal reproduction occurs by two modes of action, including both sexual and asexual reproduction. In asexual reproduction the generation of new organisms does not require the fusion sperm with an egg. However, in sexual reproduction new organisms are formed by the fusion of haploid sperm and eggs resulting in what is known as the zygote. Although animals exhibit both sexual and asexual reproduction the vast majority of animals reproduce by sexual reproduction.

They occasionally produce diploid planozygotes (mobile zygotes) implying they are capable of sexual reproduction. They have been observed to be in what appears to be the process of conjugation, a type of unicellular sexual reproduction. They can enter a hypnozygote cyst stage, which is an often thick walled, resting cyst that results from sexual fusion. This occurs when environmental conditions are adverse and allows it to be dormant and spread to grow algal blooms elsewhere.

More heritable phenotypic variation means more evolvability. While mutation is the ultimate source of heritable variation, its permutations and combinations also make a big difference. Sexual reproduction generates more variation (and thereby evolvability) relative to asexual reproduction (see evolution of sexual reproduction). Evolvability is further increased by generating more variation when an organism is stressed, and thus likely to be less well adapted, but less variation when an organism is doing well.

To ensure a successful mating, the development and release of gametes is highly synchronized and regulated; pheromones may play a key role in these processes. Sexual reproduction allows for more variation and provides the benefit of efficient recombinational repair of DNA damages during meiosis, a key stage of the sexual cycle. However, sexual reproduction is more costly than asexual reproduction. Meiosis has been shown to occur in many different species of algae.

The cape bee Apis mellifera subsp. capensis can reproduce asexually through a process called thelytoky. The freshwater crustacean Daphnia reproduces by parthenogenesis in the spring to rapidly populate ponds, then switches to sexual reproduction as the intensity of competition and predation increases. Monogonont rotifers of the genus Brachionus reproduce via cyclical parthenogenesis: at low population densities females produce asexually and at higher densities a chemical cue accumulates and induces the transition to sexual reproduction.

Antipathes dendrochristos growing several hundred meters down in the ocean Little is known about sexual reproduction in these corals. Sexual reproduction occurs after the coral colony is established. A colony will produce eggs and sperm, which meet in the water to create larvae that use currents to disperse and settle in new areas. The larval stage of the coral, called a planula, will drift along until it finds a surface on which it can grow.

Sexual differentiation in peafowl Although sexual reproduction is defined at the cellular level, key features of sexual reproduction operate within the structures of the gamete cells themselves. Notably, gametes carry very long molecules called DNA that the biological processes of reproduction can "read" like a book of instructions. In fact, there are typically many of these "books", called chromosomes. Human gametes usually have 23 chromosomes, 22 of which are common to both sexes.

They lack flagella and do not form either oocysts or spores. The known vectors are ticks or leeches in which they undergo sporogony; sexual reproduction probably occurs in the vector.

Sexual reproduction involves the production of ascospores, commencing with the fusion of an archegonium and an antheridium, with sharing of nuclei. The irregularly distributed asci contain eight unicellular ascospores each.

Species in this family are homoxenous. Gametocytes - not described Spores - not described Both gamonts and trophozoites are septate. The gamonts are morphologically different (anisogamous). Sexual reproduction involves a cephalocaudal association.

Baldacconi, R., et al. "Sexual reproduction, larval development and release in Spongia officinalis L.(Porifera, Demospongiae) from the Apulian coast." Marine Biology 152.4 (2007): 969-979. Baldacconi, Rossella, et al.

The term heterosexual or heterosexuality is usually applied to humans, but heterosexual behavior is observed in all other mammals and in other animals, as it is necessary for sexual reproduction.

Sexual reproduction shows considerable variation in the type and formation of sex cells and it may be isogamous e.g. Chlamydomonas, Ulothrix, Spirogyra, anisogamous e.g. Chlamydomonas, Eudorina or Oogamous e.g. Chlamydomonas, Volvox.

There are no known mechanisms for sexual reproduction, yet members of the genus continue to speciate. Some species can form marginal lobes and appear squamulose. It is in the family Stereocaulaceae.

Gametophytes have not been identified in the field although there is circumstantial evidence that sexual reproduction does take place.Richards, P.W., Evans, G.B. (1972). Biological Flora of the British Isles. No. 126.

In the first stage of sexual reproduction, "meiosis", the number of chromosomes is reduced from a diploid number (2n) to a haploid number (n). During "fertilisation", haploid gametes come together to form a diploid zygote, and the original number of chromosomes is restored. Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete (such as a sperm or egg cell) with a single set of chromosomes (haploid) combines with another to produce an organism composed of cells with two sets of chromosomes (diploid).John Maynard Smith & Eörz Szathmáry, The Major Transitions in Evolution, W. H. Freeman and Company, 1995, p 149 Sexual reproduction is the most common life cycle in multicellular eukaryotes, such as animals, fungi and plants.

Syllid polychaete budding epitokes for the purpose of sexual reproduction. Alitta succinea (common clam worm) in epitoky stage Epitoky is a process that occurs in many species of polychaete marine worms wherein a sexually immature worm (the atoke) is modified or transformed into a sexually mature worm (the epitoke). Epitokes are pelagic morphs capable of sexual reproduction. Unlike the immature form, which is typically benthic (lives on the bottom), epitokes are specialized for swimming as well as reproducing.

Eukaryotic organisms often use sexual reproduction to generate offspring that contain a mixture of genetic material inherited from two different parents. The process of sexual reproduction alternates between forms that contain single copies of the genome (haploid) and double copies (diploid). Haploid cells fuse and combine genetic material to create a diploid cell with paired chromosomes. Diploid organisms form haploids by dividing, without replicating their DNA, to create daughter cells that randomly inherit one of each pair of chromosomes.

A picture of the mating type mechanism has begun to emerge from studies of particular fungi such as S. cerevisiae. The mating type genes are located in homeobox and encode enzymes for production of pheromones and pheromone receptors. Sexual reproduction thereby depends on pheromones produced from variant alleles of the same gene. Since sexual reproduction takes place in haploid organisms, it cannot proceed until complementary genes are provided by a suitable partner through cell or hyphal fusion.

S. rosetta can be induced to undergo sexual reproduction by the marine bacterium Vibrio fischeri. A single protein of V. fischeri, EroS, fully recapitulates the aphrodesiac-like activity of living V. fischeri.

Sexual selection, social competition, and speciation. Quart. Rev. Biol. 58(2):155-183. She has noted how sexual selection can trap animals into sexual dimorphisms, to maintain separate sexes in sexual reproduction.

Several factors limit the amount of information regarding the life history of Elkhorn coral. These factors include the necessity for additional tools to assess future population changes, sexual reproduction, and environmental disturbances.

Rubus ulmifolius is unique among subgenus Rubus in displaying normal sexual reproduction; all other species are facultative apomicts.Edees, E.S., Newton, A. and Kent, D.H., 1988. Brambles of the British Isles. Ray Society.

Fertility, though usually affected to one degree or another—especially in males—is not always impaired significantly enough to prevent sexual reproduction, as evidenced by vertical transmission of the condition by both sexes.

In these subjects they learn about the habits of mind. In term 4 they focus on sexual reproduction and puberty which is a good time to talk about their changes in their bodies.

Evidence for sexual reproduction has been reported in the choanoflagellate species Salpingoeca rosetta. Also evidence has been reported for the presence of conserved meiotic genes in the choanoflagellates Monosiga brevicollis and Monosiga ovata.

Some insects use parthenogenesis, a process in which the female can reproduce and give birth without having the eggs fertilized by a male. Many aphids undergo a form of parthenogenesis, called cyclical parthenogenesis, in which they alternate between one or many generations of asexual and sexual reproduction. In summer, aphids are generally female and parthenogenetic; in the autumn, males may be produced for sexual reproduction. Other insects produced by parthenogenesis are bees, wasps and ants, in which they spawn males.

The earliest eukaryotes were likely protists. Although sexual reproduction is widespread among extant eukaryotes, it seemed unlikely until recently, that sex could be a primordial and fundamental characteristic of eukaryotes. A principal reason for this view was that sex appeared to be lacking in certain pathogenic protists whose ancestors branched off early from the eukaryotic family tree. However, several of these protists are now known to be capable of, or to recently have had the capability for, meiosis and hence sexual reproduction.

An unstained T. gondii tissue cyst, 200px Like tachyzoites, merozoites divide quickly, and are responsible for expanding the population of the parasite inside the cat's intestine before sexual reproduction. When a feline definitive host consumes a tissue cyst (containing bradyzoites), bradyzoites convert into merozoites inside intestinal epithelial cells. Following a brief period of rapid population growth in the intestinal epithelium, merozoites convert into the noninfectious sexual stages of the parasite to undergo sexual reproduction, eventually resulting in zygote-containing oocysts.

Another theory is that sexual reproduction originated from selfish parasitic genetic elements that exchange genetic material (that is: copies of their own genome) for their transmission and propagation. In some organisms, sexual reproduction has been shown to enhance the spread of parasitic genetic elements (e.g. yeast, filamentous fungi). Bacterial conjugation is a form of genetic exchange that some sources describe as "sex", but technically is not a form of reproduction, even though it is a form of horizontal gene transfer.

In euglenoids, sexual reproduction is unknown; however, asexual reproduction has been observed to occur in this genus through longitudinal fission, where the division occurs very quickly, starting at the anterior end of the cell.

Rhizopus stolonifer can reproduce asexually and sexually. It is a heterothallic species. Sexual reproduction occurs when compatible mating strains are paired, ultimately giving rise to zygospores. The sporangiophore contains both '+' and '−' mating type strains.

Cells that can unite may then undergo conjugation. Sexual reproduction involving interaction of opposite mating types promotes outcrossing and the masking of deleterious recessive mutations in the diploid stage of the sexual life cycle.

Sachs has been described as a "post-Darwinian botanist" who "integrated the evolutionary theory into his morphological writings."Farley, John. (1982). Gametes & Spores: Ideas about Sexual Reproduction, 1750-1914. Johns Hopkins University Press. p.

Diplonemidae are capable of sexual reproduction, as genes involved in meiosis have been found. Although marine diplonemids appear to reproduce sexually, not much is known about Diplonemidae reproduction as Euglenozoans rarely demonstrate sexual processes.

Little is known regarding the mating behavior of black- spotted cuscuses. Courting is typically performed on tree limbs. Black-spotted cuscuses produce offspring via sexual reproduction. They are viviparous, with the mother birthing live young.

He was also an enthusiastic educatorFor example: and the author of several books on insects, evolution and sexual reproduction. He is best remembered as an ardent supporter and champion of experiments on peppered moth evolution.

Puccinia monoica is a parasitic rust fungus of the genus Puccinia that inhibits flowering in its host plant (usually an Arabis species) and radically transforms host morphology in order to facilitate its own sexual reproduction.

Some species of planaria are exclusively asexual, whereas some can reproduce both sexually and asexually. In most of the cases the sexual reproduction involve two individuals; autofecundation has been rarely reported (e.g. in Cura foremanii).

It has not yet been possible to observe fertilisation itself; the existence of the fertilisation membrane is currently taken to be evidence, however, that it has taken place. Putative eggs have been observed, but they degrade typically at the 32–64 cell stage. Neither embryonic development nor sperm have been observed. Despite lack of observation of sexual reproduction in lab, the genetic structure of the populations in wild is compatible with the sexual reproduction mode, at least for species of the analysed genotype H5.

A link between vasopressin release and aggression has been observed in females, which may impair female sexual reproduction arousal and sexual motivation by leading to feelings of neglect and hostility toward a sexual partner. In males, vasopressin is involved in the arousal phase. Vasopressin levels have been shown to increase during erectile response in male sexual reproduction arousal, and decrease back to baseline following ejaculation. The increase of vasopressin during erectile response may be directly associated with increased motivation to engage in sexual behaviour.

When a suitable medium is located, the hairs surrounding the spore will lock onto the substrate so that the sexual reproduction phase can start. It is also during this stage of polyplanetism that the Saprolegnia are capable of causing infection; the most pathogenic species have tiny hooks at the end of their hairs to enhance their infectious ability. Once firmly attached, sexual reproduction begins with the production of male and female gametangium, antheridia and oogonium respectively. These unite and fuse together via fertilization tubes.

During sexual reproduction there is a diploid phase, which commonly is very short, and meiosis restores the haploid state. The sexual cycle of one well-studied representative species of Ascomycota is described in greater detail in Neurospora crassa. Also, the adaptive basis for the maintenance of sexual reproduction in the Ascomycota fungi was reviewed by Wallen and Perlin. They concluded that the most plausible reason for the maintenance of this capability is the benefit of repairing DNA damage by using recombination that occurs during meiosis.

In any case, outcross matings provide the benefit of masking deleterious recessive alleles in progeny. This benefit has been proposed to be a major factor in the maintenance of sexual reproduction among eukaryotes, as summarized in the article Evolution of sexual reproduction. An epigenetic contribution to heterosis has been established in plants, and it has also been reported in animals. MicroRNAs (miRNAs), discovered in 1993, are a class of non-coding small RNAs which repress the translation of messenger RNAs (mRNAs) or cause degradation of mRNAs.

Vegetative cell division occurs over hundreds of generations for C. meneghiniana, with the cell diameters of the offspring organisms becoming gradually smaller. Regardless of the flexibility of the girdle bands and functionality of vegetative cell division, there is a point where the diameter of C. meneghiniana offspring dips below a certain threshold diameter. It has been observed that at this point, species-specific environmental stimuli induces the change from asexual reproduction to sexual reproduction. Sexual reproduction occurs with gametes being formed upon reaching the threshold.

Heliconius has evolved two forms of mating. The main form is standard sexual reproduction. Some species of Heliconius, however, have converged evolutionarily in regard to pupal mating. One species to exhibit this behavior is Heliconius charithonia.

While all prokaryotes reproduce without the formation and fusion of gametes, mechanisms for lateral gene transfer such as conjugation, transformation and transduction can be likened to sexual reproduction in the sense of genetic recombination in meiosis.

Both sexual and asexual reproductions are implemented. Asexual reproduction is implemented as producing the offspring's genome (the gene network) by directly copying the parent's genome. Sexual reproduction is implemented as the recombination of the two parents' genomes.

One mobile organism with substantial phenotypic plasticity is Acyrthosiphon pisum of the aphid family, which exhibits the ability to interchange between asexual and sexual reproduction, as well as growing wings between generations when plants become too populated.

Serpula himantioides has a heterothallic tetrapolar mating system. This means it requires the growth and conjugation of two mating types, determined by the expression of one or more alleles of two unlinked mating loci, for sexual reproduction.

Sexual reproduction also sometimes occurs and eggs and sperm are released into the water. They unite and form free-swimming larvae which are initially planktonic. Later they settle and adhere to the substrate, growing into new individuals.

The styles are 1 mm long and glabrous. Plants are for the most part self-sterile and dependent on pollinators for sexual reproduction. Pollinators include bumblebees, solitary bees, beeflies, and syrphid flies.Barrett, Spencer C.; Helenurm, Kaius. 1987.

Sexual reproduction results in the formation of a zygospore that functions as a resting spore. The zygospore is formed by the fusion of gametangial cells or the scalariform fusion of hyphae. Little is known about the zygospores.

The larvae or newly settled polyps can acquire symbiotic algae from the environment. External factors affect the method of reproductions. Asexual reproduction is used more when conditions are bad. Sexual reproduction is used when conditions are good.

Sexual reproduction in the animal world is facilitated through opposite-sex sexual activity, although there are also animals that reproduce asexually, including protozoa and lower invertebrates.The Columbia Encyclopedia (Colum. Univ. Press, 5th ed. [casebound?] 1993 ()), entry Reproduction.

Although the evolution of sex took place before the origin of animals, and evidence of sexual reproduction is observed in red algae , Funisia is one of the oldest known animals for which there is evidence of sexual reproduction. Its relationship to other animals is unknown, but it may belong within the Porifera (sponges) or Cnidaria, or it may have been a basal metazoan.D. H. Erwin, M. Laflamme, S., M. Tweedt, E. A. Sperling, D. Pisani, and K. J. Peterson. 2011. The Cambrian Conundrum: Early Divergence and Later Ecological Success in the Early History of Animals.

To cite one example, the common intestinal parasite Giardia intestinalis was once considered to be a descendant of a protist lineage that predated the emergence of meiosis and sex. However, G. intestinalis was recently found to have a core set of genes that function in meiosis and that are widely present among sexual eukaryotes. These results suggested that G. intestinalis is capable of meiosis and thus mating and sexual reproduction. Furthermore, direct evidence for meiotic recombination, indicative of mating and sexual reproduction, was also found in G. intestinalis.

These haploid individuals give rise to gametes through mitosis. Meiosis and gamete formation therefore occur in separate generations or "phases" of the life cycle, referred to as alternation of generations. Since sexual reproduction is often more narrowly defined as the fusion of gametes (fertilization), spore formation in plant sporophytes and algae might be considered a form of asexual reproduction (agamogenesis) despite being the result of meiosis and undergoing a reduction in ploidy. However, both events (spore formation and fertilization) are necessary to complete sexual reproduction in the plant life cycle.

Technically the problem above is not one of sexual reproduction but of having a subset of organisms incapable of bearing offspring. Indeed, some multicellular organisms (isogamous) engage in sexual reproduction but all members of the species are capable of bearing offspring. The two-fold reproductive disadvantage assumes that males contribute only genes to their offspring and sexual females waste half their reproductive potential on sons. Thus, in this formulation, the principal cost of sex is that males and females must successfully copulate, which almost always involves expending energy to come together through time and space.

Some of the species within Basidiomycota have the most complex systems of sexual reproduction known among Fungi. In general for Fungi there are two main types of sexual reproduction: homothallism, when mating occurs within a single individual, or in other words each individual is self-fertile; and heterothallism, when hyphae from a single individual are self-sterile and need to interact with another compatible individual for mating to take place. Additionally, mating compatibility in the Basidiomycota is further categorized into two types of mating systems: tetrapolar and bipolar.

Fly pushing: the theory and practice of drosophila genetics. Cold Spring Harbor (N.Y.): Cold Spring Harbor Laboratory Press. Using this system, a proportion of the offspring created by sexual reproduction will inherit a balancer chromosome and its homologue.

Springer-Verlag, New York. 343 pp. Lichtwardt, R. W., and Williams, M. C. 1988. Discovery of sexual reproduction in an unusual new species of Stachylina (Trichomycetes). Mycologia 80: 400–405. Lichtwardt, R. W., and Williams, M. C. 1990.

There is a single median compound eye. Most species show cyclical parthenogenesis, where asexual reproduction is occasionally supplemented by sexual reproduction, which produces resting eggs that allow the species to survive harsh conditions and disperse to distant habitats.

Eukaryotic genomes evolve over time through many mechanisms including sexual reproduction which introduces much greater genetic diversity to the offspring than the prokaryotic process of replication in which the offspring are theoretically genetic clones of the parental cell.

The phylum Ascomycota or sac fungus is characterized by formation of meiotic spores called ascospores enclosed in a special sac called an ascus. The genetic components for sexual reproduction appear to be produced by all members of this group.

Albuca bracteata can undergo vegetative and sexual reproduction. Propagation via bulblets is the most common method, whereby the bulblets are separated from the mother bulb and planted. Seed production provides genetic variation. Micropropagation of Albuca bracteata has been achieved.

Sexual reproduction takes place with gametes being released into the water column where fertilisation takes place. The larvae that develop from the eggs are planktonic and drift with the currents before settling on the seabed to found new colonies.

Periodically sexual reproduction takes place. It is not known why this occurs at some times and not others. The female undergoes meiosis and produces eggs with half the usual number of chromosomes. Some of these develop into male rotifers.

The sexual population in the same situation will remain diverse enough to survive changing environments. From this theory, Roughgarden concludes that the main benefit of sexual reproduction is the maintenance of genetic diversity when compared to similar asexual populations.

Many members of the Hydrozoa go through a body change from a polyp to an adult form called a medusa, which is usually the life stage where sexual reproduction occurs, but Hydra do not progress beyond the polyp phase.

The schizonts develop into merozoites which eventually cause host cell rupture and enter the blood. These intravascular merozoites infect variable numbers of erythrocytes. An infected host is then bitten by a tick. The parasites undergo sexual reproduction in the tick's gut.

Calliactis tricolor can reproduce asexually by longitudinal fission. Prior to that observation, its method of reproduction was unknown, but the finding of a number of very small specimens in one location indicates that sexual reproduction may also sometimes take place.

Sexual Reproduction in Humans. 2006. John W. Kimball. Kimball's Biology Pages, and online textbook. The female reproductive system has two functions: The first is to produce egg cells, and the second is to protect and nourish the offspring until birth.

Auxospore formation by the silica-sinking, oceanic diatom Fragilariopsis kerguelensis (Bacillariophyceae). J. Phycol. 42, 1002-1006. Auxospores can also play a role in sexual reproduction in diatoms, and may be formed after haploid gametes fuse to form a diploid zygote.

Deacon, p. 31. Sexual reproduction in basidiomycetes is similar to that of the ascomycetes. Compatible haploid hyphae fuse to produce a dikaryotic mycelium. However, the dikaryotic phase is more extensive in the basidiomycetes, often also present in the vegetatively growing mycelium.

Piroplasmida is an order of parasites in the phylum Apicomplexa. They divide by binary fission and as sporozoan parasites they possess sexual and asexual phases (sexual reproduction occurs in the tick gut). They include the tick parasites Babesia and Theileria.

Tanja Schwander's work has focused on understanding the consequences of asexuality using Timema stick insects as a model system. Her work has contributed to the current understanding of the Evolution of sexual reproduction, the Paradox of Sex, and Sexual conflict.

At times of food scarcity, however, the anemone may consume the zooxanthellae. Reproduction can take place by fission, the anemone splitting in half longitudinally. The offspring are clones of the parent and genetically identical. Alternatively, sexual reproduction occurs, with internal fertilisation.

Sexual reproduction has never been observed. It suffers grazing pressure from gastropods and amphipods, but amazingly fragments of the algae are able to pass through the grazers' digestive tracts alive - grazing may actually form a mode of dispersal for the organism.

As a cnidarian, this jellyfish has an asexual and sexual reproduction. It reproduces by budding when it is in a polyp form. When it is in a medusa form, it reproduces sexually. The medusa female produces the eggs and keeps them.

Sexual reproduction can also occur with eggs being liberated into the sea by the adult medusa. When fertilised, these develop into a free-living planula, then to a scyphistoma, to a strobila, and lastly to a free-living young medusa.

Sexual reproduction occurs by the release of gametes into the water column. The planula larvae drift with the currents before settling on the seabed and undergoing metamorphosis into polyps. These begin to secrete their own skeletons and found new colonies.

One is an unknown threat probably related to the plant's biology that is evidenced by its absence in large stretches of appropriate habitat and its absence from an assemblage of surviving native plants. It may have low rates of sexual reproduction.

Monogamous pairing refers to a general relationship between an adult male and an adult female for the purpose of sexual reproduction. It is particularly common in birds, but there are examples of this occurrence in reptiles, invertebrates, fish, amphibians, and mammals.

Species in this group are short cycled. The zoospore nucleus forms a sorus. Resting spores are either unknown or truly absent. To date, sexual reproduction is only described in four species: Synchytrium endobioticum, S. fulgens, S. macroporosum, and S. psophocarpi.

Abundant evidence indicates that facultative sexual eukaryotes tend to undergo sexual reproduction under stressful conditions. For instance, the budding yeast Saccharomyces cerevisiae (a single-celled fungus) reproduces mitotically (asexually) as diploid cells when nutrients are abundant, but switches to meiosis (sexual reproduction) under starvation conditions. The unicellular green alga, Chlamydomonas reinhardtii grows as vegetative cells in nutrient rich growth medium, but depletion of a source of nitrogen in the medium leads to gamete fusion, zygote formation and meiosis. The fission yeast Schizosaccharomyces pombe, treated with H2O2 to cause oxidative stress, substantially increases the proportion of cells which undergo meiosis.

Conjugal DNA transfer in M. smegmatis requires stable and extended contact between a donor and a recipient strain, is DNase resistant, and the transferred DNA is incorporated into the recipient’s chromosome by homologous recombination. However, in contrast to the well-known E. coli Hfr conjugation system, in M. smegmatis all regions of the chromosome are transferred with comparable efficiencies and mycobacterial conjugation is chromosome, rather than plasmid based. Gray et al. reported substantial blending of the parental genomes resulting from conjugation and referred to this blending as reminiscent of that seen in the meiotic products of sexual reproduction (see Origin of sexual reproduction).

Ulocladium botrytis is an anamorphic fungus, thus it undergoes asexual reproduction. Although it is an asexual fungus, U. botrytis possesses the mating type locus, which consists of two dissimilar DNA sequences termed MAT1-1-1 and MAT1-2-1. These U. botrytis MAT genes are essential for controlling colony size and asexual traits such as conidial size and number in U.botrytis. The U. botrytis MAT genes have lost the ability to regulate sexual reproduction in U. botrytis; however, they have the ability to partially induce sexual reproduction in Cochliobolus heterostrophus, a heterothallic species, upon heterologous complementation.

The maintenance of sexual reproduction (specifically, of its dioecious form) by natural selection in a highly competitive world has long been one of the major mysteries of biology, since both other known mechanisms of reproduction – asexual reproduction and hermaphroditism – possess apparent advantages over it. Asexual reproduction can proceed by budding, fission, or spore formation and does not involve the union of gametes, which accordingly results in a much faster rate of reproduction compared to sexual reproduction, where 50% of offspring are males and unable to produce offspring themselves. In hermaphroditic reproduction, each of the two parent organisms required for the formation of a zygote can provide either the male or the female gamete, which leads to advantages in both size and genetic variance of a population. Sexual reproduction therefore must offer significant fitness advantages because, despite the two-fold cost of sex (see below), it dominates among multicellular forms of life, implying that the fitness of offspring produced by sexual processes outweighs the costs.

In 1973, Leigh Van Valen proposed the term "Red Queen," which he took from Through the Looking-Glass by Lewis Carroll, to describe a scenario where a species involved in one or more evolutionary arms races would have to constantly change just to keep pace with the species with which it was co-evolving. Hamilton, Williams and others suggested that this idea might explain the evolution of sexual reproduction: the increased genetic diversity caused by sexual reproduction would help maintain resistance against rapidly evolving parasites, thus making sexual reproduction common, despite the tremendous cost from the gene-centric point of view of a system where only half of an organism's genome is passed on during reproduction. However, contrary to the expectations of the Red Queen hypothesis, Hanley et al. found that the prevalence, abundance and mean intensity of mites was significantly higher in sexual geckos than in asexuals sharing the same habitat.

Not much research has been done into the reproduction of Geminigera, but the organism has been shown to reproduce asexually by fission. It is unknown if any sexual reproduction occurs within Geminigera or whether it has an alternation of generations like other cryptomonads.

A. spiraecola is an holocyclic species, meaning that they undergo sexual reproduction during part of its life cycle and reproduces entirely parthenogenetically over most of its geographical range. Where it is holocyclic and produces sexual morphs, the primary hosts are Spiraea or Citrus.

This species reproduces sexually and asexually. In sexual reproduction, it produces small yellow fruiting bodies known as ascocarps. These ascomata are 45-95 μm spheres with dark, thick walls. Within the ascomata are many asci; these asci are thin- walled and disintegrate easily.

Efforts to understand gene conversion at the molecular level have provided important insights into the mechanism and adaptive function of meiotic recombination, which in turn bears on the adaptive function of sexual reproduction. These insights are discussed further in the article Gene conversion.

A hydra vulgaris with 6 tentacles. This species can reproduce in three ways: sexual reproduction, budding, and indirectly through regeneration.Working with Hydra, Ward's Science 2002. When hydra reproduce sexually, simple testes, ovaries, or both will develop on the bodies of an individual.

Replication of Cryptomonas occurs in early summer when fresh water species are also reproducing. Cryptomonas replicates via mitosis that only takes about ten minutes. Sexual reproduction is not observed in this genus as many other genera of Cryptophytes also do not reproduce sexually.

The pathogen breaks through the surface of leaves and flowering structures through stomata. Asexual reproduction structures, called zoosporangiaphores, form at these sites. These structures release zoosporangia containing zoospores to other plants, the primary means of dissemination. Sexual reproduction be either homothallic or heterothallic.

S. turcica is a heterothallic fungus, meaning that a single isolate cannot mate with itself. Instead, two isolates with complementary mating type genes are required for sexual reproduction. The "perfect stage" (sexual stage or teleomorph) was first described in 1958.Luttrell, ES. 1958.

The Relative Contributions of Sexual Reproduction and Clonal Propagation in Opuntia rastrera from Two Habitats in the Chihuahuan Desert, Maria del Carmen Mandujano, Carlos Montana, Ignacio Mendez, Jordan Golubov, The Journal of Ecology, Vol. 86, No. 6 (Dec., 1998), pp. 911-921.

The Red Queen Hypothesis, for example, posits that parasites track down and specialize on the locally common genetic defense systems of its host that drives the evolution of sexual reproduction to diversify the genetic constituency of populations responding to the antagonistic pressure.

They reproduce by broadcast spawning, releasing eggs and sperm into the sea to achieve fertilization. Some anemones are able to reproduce by fission, in essence cloning themselves. It is unknown whether this anemone is capable of asexual fission in addition to sexual reproduction.

Nearly all vertebrates undergo sexual reproduction. They produce haploid gametes by meiosis. The smaller, motile gametes are spermatozoa and the larger, non-motile gametes are ova. These fuse by the process of fertilisation to form diploid zygotes, which develop into new individuals.

Plant species in the tundra are relatively slow growing, long- lived, perennial organisms devoting minimal resources to sexual reproduction and would be categorized as severe K-strategists.Molau, Ulf. "Relationships between Flowering Phenology and Life History Strategies in Tundra Plants." Arctic and Alpine Research.

In addition to ordinary sexual reproduction, Corynactis viridis reproduces by means of longitudinal fission; in this process two sides of the anemone draw apart from each other, tearing the animal in half, after which both of the fragments heal and become new individuals.

Not much is known about the life cycle of C. exigua. It exhibits sexual reproduction. It is likely that juveniles first attach to the gills of a fish and become males. As they mature, they become females, with mating likely occurring on the gills.

Most jovibarbas, like sempervivums, reproduce via offsets in addition to producing seeds via sexual reproduction. Jovibarba heuffelii does not produce offsets on stolons. Instead the offspring of this plant are produced within the mother plant. To propagate it must be split with a knife.

Species Profiles for Pacific Island Agroforestry, Feb. 2007 ver. 1 This fact means that the plants are spread by conventional vegetative methods and lack sexual reproduction. This lack of genetic diversity makes Grand Naines as well as other AAA cultivars vulnerable to diseases and pests.

Carotenes produced from carotenoids are further processed by carotene oxygenase to synthesize trisporic acid (TSA). TSA produced from carotene stimulates both sexually complementary cells to make contact with each other. TSA is considered an important signalling molecule for the initiation and control sexual reproduction.

Caudofoveates live by burrowing through soft sediment, and feed by lying vertically in the sediment with just the mouthparts exposed and taking in passing organic detritus. During sexual reproduction, the female produces eggs which are fertilized and brooded, and then the larvae swim freely.

Protists are a large group of diverse eukaryotic microorganisms, mainly unicellular animals and plants, that do not form tissues. Eukaryotes emerged in evolution more than 1.5 billion years ago. The earliest eukaryotes were likely protists. Mating and sexual reproduction are widespread among extant eukaryotes.

Via sexual reproduction, and sexes are generally separate, however some hermaphrodites have been found. Population sex ratio is 1:1. Reproductive season is from October to February,Sewell, M. A. and P. R. Berquist. 1990. Variability in the reproductive cycle of Stichopus mollis (Echinodermata:Holothuroidea).

In the rotifer Brachionus calyciflorus asexual reproduction (obligate parthenogenesis) can be inherited by a recessive allele, which leads to loss of sexual reproduction in homozygous offspring. Inheritance of asexual reproduction by a single recessive locus has also been found in the parasitoid wasp Lysiphlebus fabarum.

However, it does support the "selfish gene" part theory, since the gene itself is propagated through the F-plasmid. A similar origin of sexual reproduction is proposed to have evolved in ancient haloarchaea as a combination of two independent processes: jumping genes and plasmid swapping.

Sexual reproduction requires that a sperm fertilize an egg which grows into a larva. Currents then disperse the larvae. Growth begins when the larvae attach to a solid substrate. Old/dead coral provides an excellent substrate for this growth, creating ever higher mounds of coral.

Spongia officinalis can reproduce asexually via budding or fragmentation. Sexual reproduction is also common in S. officinalis. Individuals can be dioecious, either male or female, or sequential hermaphrodites, meaning they can alternate between male and female. Successive hermaphroditism can take place within one reproductive season.

A. conandae reproduces by fission in addition to sexual reproduction, which takes place at the beginning of the summer. The gonopores (genital openings) are located on the upper side, and the observed sex ratio is 52 males per 93 females, but some specimens are hermaphrodites.

Rolling Hen-and-chicks produce small globe-shaped offsets ("globi") that are lightly attached and easily pop off and roll away from the mother plant. Offsets survive the main rosette, which is monocarpic. They reproduce via offsets in addition to producing seeds via sexual reproduction.

Sexual reproduction, early development and branching in Notheia anomala (phaeophyta) and its classification in the Fucales. Phycologia, 26(3), 363-373.Raven, J. A., Beardall, J., Johnston, A. M., Kuebler, J. E., & McInroy, S. G. (1996). Inorganic carbon acquisition by Xiphophora chondrophylla (Phaeophyta, Fucales).

The origin and function of meiosis are currently not well understood scientifically, and would provide fundamental insight into the evolution of sexual reproduction in eukaryotes. There is no current consensus among biologists on the questions of how sex in eukaryotes arose in evolution, what basic function sexual reproduction serves, and why it is maintained, given the basic two-fold cost of sex. It is clear that it evolved over 1.2 billion years ago, and that almost all species which are descendants of the original sexually reproducing species are still sexual reproducers, including plants, fungi, and animals. Meiosis is a key event of the sexual cycle in eukaryotes.

According to Jennifer Robertson of the University of Michigan, eugenism, as part of the new scientific order, was introduced in Japan "under the aegis of nationalism and empire building." She identifies "positive eugenism" and "negative eugenism." Positive eugenism, promoted by Ikeda Shigenori, refers to "the improvement of circumstances of sexual reproduction and thus incorporates advances in sanitation, nutrition and physical education into strategies to shape the reproductive choices and decisions of individual and families" Negative Eugenism, promoted by Hisomu Nagai, "involves the prevention of sexual reproduction, through induced abortion or sterilization among people deemed unfit". "Unfit" included people such as alcoholics, lepers, the mentally ill, the physically disabled, and criminals.

Reproduce sexually (sexual reproduction is oogamous) and asexually [Guiry 2011]. Skeletonema belong to the morphological category referred to as centric diatoms. These are classified by having valves with radial symmetry and the cells lack significant motility [Horner 2002]. Skeletonema are cylindrical shaped with a silica frustule.

The fruit is up to 2.5 centimeters long including its hairy, elongated beak. Sexual reproduction is rare in this species, which undergoes vegetative reproduction by sprouting repeatedly from its rhizome.Timmerman-Erskine, M. and R. S. Boyd. (1999). Reproductive biology of the endangered plant Clematis socialis (Ranunculaceae).

This result is consistent with the Red Queen hypothesis that sexual reproduction is favoured during host–parasite coevolution. At the same time, the persistence of sex may also rely on other factors, for example Muller's ratchet and/or the avoidance of the accumulation of deleterious mutations.

Only one type of zoospore will emerge from any single host. Once the zoospores exit the host, the life stages of Syndinium are not well understood. Attempts to infect copepod hosts or to induce sexual reproduction between all combinations of zoospores have so far been unsuccessful.

Narnavirus is a genus of positive-strand RNA viruses, in the family Narnaviridae. Fungi serve as natural hosts. There are currently two species in this genus including the type species Saccharomyces 20S RNA narnavirus. Narnaviruses have been shown to be required for sexual reproduction of Rhizopus microsporus.

In the latter case, the sporangia behave as conidia and are often referred to as such. Sexual reproduction is via oospores. The parasitised plants are angiosperms or gymnosperms, and most Peronosporaceae are pathogens of herbaceous dicots. Some downy mildew genera have a more restricted host range, e.g.

The narrow- banded shovel-nosed snake is a nocturnal fossorial species, burrowing in sandy habitats. This species emerges to the surface on warm nights to forage for food. Reproduction occurs via sexual reproduction. This snake is oviparous with an average clutch size of three to five eggs.

It has been observed, however, that certain taxa have the ability to divide without causing a reduction in cell size. Nonetheless, in order to restore the cell size of a diatom population for those that do endure size reduction, sexual reproduction and auxospore formation must occur.

Zygospores range in size from 40-80μm. They are spherical or slightly flattened in shape. Blakeslea trispora has a heterothallic mating system, having (+) and (-) mating types. Contact and interchange between the opposite mating types is a necessary precursor to induce sexual reproduction and development of zygospores.

Other protists for which evidence of mating and sexual reproduction has recently been described are parasitic protozoa of the genus Leishmania, Trichomonas vaginalis, and acanthamoeba. Protists generally reproduce asexually under favorable environmental conditions, but tend to reproduce sexually under stressful conditions, such as starvation or heat shock.

Killing was abhorrent to the Cathars. Consequently, abstention from all animal food (sometimes exempting fish) was enjoined of the Perfecti. The Perfecti avoided eating anything considered to be a by-product of sexual reproduction. War and capital punishment were also condemned—an abnormality in Medieval Europe.

Craticula is a genus of diatom that lies on or in the top layers of sediments in the freshwater to brackish water environments it inhabits. In addition to frustule morphology the genus differs from closely related species by its sexual reproduction and movement in response to light.

As well as sexual reproduction by seed, many butterworts can reproduce asexually by vegetative reproduction. Many members of the genus form offshoots during or shortly after flowering (e.g., P. vulgaris), which grow into new genetically identical adults. A few other species form new offshoots using stolons (e.g.

Diactines may be added. Asconoid aquiferous system. Arturia canariensis, for example, is a filter feeder, sieving plankton and other organic material out of the current of water as it passes through the ostia. Both asexual reproduction by budding and sexual reproduction take place in Arturia canariensis.

Most insects reproduce via sexual reproduction, i.e. the egg is produced by the female, fertilised by the male and oviposited by the female. Eggs are usually deposited in a precise microhabitat on or near the required food. However, some adult females can reproduce without male input.

However, experts in the field believe that major innovations are required before immunocontraception can become a practical form of contraception for human beings. Thus far immunocontraception has focused on mammals exclusively. There are several targets in mammalian sexual reproduction for immune inhibition. They can be organized into three categories.

Most strains are haploid, mating very rarely and diploidize transiently by somatogamous autogamy (i.e. fusion of two cells but excluding their nuclei). Sexual reproduction proceeds via heterogamous conjugation (i.e. the conjugation of two cells of different form or size) leading to short diplophase followed by meiosis and ascospore formation.

Walsh, V.; N. Ramos; P. Faletra (2013). "Characterization of Cypripedium species and Habitats in New Hampshire." AAAS annual Symposium Abstracts. Although a single seed pod can produce over 50,000 seeds, low germination and a seed-to-flowering term of about 8 years indicate that sexual reproduction is inefficient.

Members of the Monoblepharidomycetes have a filamentous thallus that is either extensive or simple and unbranched. They frequently have a holdfast at the base. In contrast to other taxa in their phylum, some reproduce using autospores, although many do so through zoospores. Oogamous sexual reproduction may also occur.

It is an almost universal attribute of polyps to reproduce asexually by the method of budding. This mode of reproduction may be combined with sexual reproduction, or may be the sole method by which the polyp produces offspring, in which case the polyp is entirely without sexual organs.

The lifecycle of P. jirovecii is thought to include both asexual and sexual phases. Asexual multiplication of haploid cells likely occurs by binary fission. The mode of sexual reproduction appears to be primary homothallism, a form of self-fertilization. The sexual phase takes place in the host's lungs.

The life cycle varies considerably. Some have a simple asexual life cycle, while others have a complex life cycle involving multiple hosts and both asexual and sexual reproduction. Different types of spores may be produced at different stages, probably with different functions including autoinfection (transmission within a single host).

Unlike a sexual cycle, the process lacks coordination and is exclusively mitotic. The parasexual cycle resembles sexual reproduction. In both cases, unlike hyphae (or modifications thereof) may fuse (plasmogamy) and their nuclei will occupy the same cell. The unlike nuclei fuse (karyogamy) to form a diploid (zygote) nucleus.

Bangiadulcis and Pseudobangia were previously thought to be part of the genus Bangia. However, it has since been discovered that these plants can only undergo asexual reproduction through the formation of archaeosporangia. In fact, sexual reproduction has so far only been recorded in Bangia, Porphyra, Erythrotrichia and Erythrocladia.

There are basically two distinct types of sexual reproduction among fungi. The first is outcrossing (in heterothallic fungi). In this case, mating occurs between two different haploid individuals to form a diploid zygote, that can then undergo meiosis. The second type is self-fertilization or selfing (in homothallic fungi).

Sexual reproduction occurs through the clustered or scattered deposition of spermatophores by male adults. Stimulation of spermatophore deposition by female pheromones has been demonstrated in Sinella curviseta. Mating behaviour can be observed in Symphypleona. Among Symphypleona, males of some Sminthuridae use a clasping organ located on their antenna.

Reproduction is mostly by stolons or by the rooting of detached fragments. Sexual reproduction does also occur, in the spring in North America, but is relatively unimportant as a means of reproduction. Individual plants are either male or female and the capsules housing the spores are seldom observed.

Eventually, a merozoite becomes a male microgamecyte and asexually reproduces in epithelial cells. A ruptured microgamecyte infects a cell with the female macrogamecyte and through sexual reproduction create a zygote. The zygote develops a protective shell before expulsion in the bile excreation and then the feces as an oocyst.

They pupate in the nest and emerge as adults the next spring. The iron cross beetle like most beetles have sexual reproduction. The species is very gender-scripted, with the male fighting to mate the female. Eggs are laid by the female in protected areas like under stones.

Although Muller discussed the advantages of sexual reproduction in his 1932 talk, it does not contain the word "ratchet". Muller first introduced the term "ratchet" in his 1964 paper, and the phrase "Muller's ratchet" was coined by Joe Felsenstein in his 1974 paper, "The Evolutionary Advantage of Recombination".

In general, under high stress conditions like nutrient starvation, haploid cells will die; under the same conditions, however, diploid cells of Saccharomyces cerevisiae can undergo sporulation, entering sexual reproduction (meiosis) and produce a variety of haploid spores, which can go on to mate (conjugate) and reform the diploid.

Teleomorphic stages of Rosellinia spp. are only occasionally observed in the wild and have never been observed in laboratory cultures. The anamorph (Dematophora spp.) is most commonly found. Because survival structures have not been produced in culture, environmental conditions that promote sexual reproduction in R. bunodes are not known.

De novo methylation is the main recognized activity of DNMT3A, which is essential for processes such as those mentioned in the introductory paragraphs. Genetic imprinting prevents parthenogenesis in mammals, and hence forces sexual reproduction and its multiple consequences on genetics and phylogenesis. DNMT3A is essential for genetic imprinting.

This occurs in springtime when the sponge forms buds in its outer layer. These will eventually drift away from the original structure to form a new colony. Sexual: The summer is when sexual reproduction occurs. These freshwater sponges are hermaphroditic, meaning that each sponge produces both sperm and egg.

Members of the genus Phytophthora may reproduce by both sexual and asexual methods. P. alni is homothallic meaning that both structures for sexual reproduction (antheridia and oogonia) appear in a single culture. The antheridia are amphigynous, except in some cultures of P. alni. multiformis where paragynous antheridia may occur.

The life cycle is unusual in that the cerambycoid stage of the larva gives birth via parthenogenesis to caraboid larvae, or more rarely, develops into an adult female. The adults of both genders are sterile, and are likely vestigial remnants of a time when the lifecycle involved sexual reproduction.

On the microscopic level, C. consortionis appears ovoid, with a thin capsule. Sexual reproduction does not occur in this species, but it asexually reproduces through budding at the birth scar site. Very occasionally, the cells have been observed to produce three celled pseudomycelia. C. consortionis does not ferment.

Nägler stated that first the pairs of nuclei in each trophozoite fuse, and then the cells fuse together in the cyst. The amoeba that arises from the cyst is thought to have two haploid nuclei, making it a diploid, thus there is no true haploid life cycle stage. Many other studies have found these bicellular, double walled cysts in both S. diploidea and S. pedata; however, the fusion of nuclei has never been documented, as they become very difficult to detect during this process, therefore the exact process of sexual reproduction (including the presence of a haploid stage) are not currently known. The encystation process is likely to be used for sexual reproduction.

The first cost is that in sexually dimorphic species only one of the two sexes can bear young. (This cost does not apply to hermaphroditic species, like most plants and many invertebrates.) The second cost is that any individual who reproduces sexually can only pass on 50% of its genes to any individual offspring, with even less passed on as each new generation passes. Yet sexual reproduction is the more common means of reproduction among eukaryotes and multicellular organisms. The Red Queen hypothesis has been used to explain the significance of sexual reproduction as a means to enable continual evolution and adaptation in response to coevolution with other species in an ever-changing environment.

Furthermore, in contrast to E. coli (Hfr) conjugation, in M. smegmatis all regions of the chromosome are transferred with comparable efficiencies. Substantial blending of the parental genomes was found as a result of conjugation, and this blending was regarded as reminiscent of that seen in the meiotic products of sexual reproduction.

P. pastoris can undergo both asexual reproduction and sexual reproduction, by budding and ascospore. In this case, two types of cells of P. pastoris exist: haploid and diploid cells. In the asexual life cycle, haploid cells undergo mitosis for reproduction. In the sexual life cycle, diploid cells undergo sporulation and meiosis.

Diplontic life cycle Haplontic life cycle. Meiosis occurs in eukaryotic life cycles involving sexual reproduction, consisting of the constant cyclical process of meiosis and fertilization. This takes place alongside normal mitotic cell division. In multicellular organisms, there is an intermediary step between the diploid and haploid transition where the organism grows.

Like many other leeches, M. montezuma is hermaphroditic. Sexual reproduction results in two individuals fertilizing each other, and the resulting eggs are placed in a nutrient-filled cocoon. The cocoon is placed deep enough to avoid the attention of ducks and other predators, and the eggs hatch into self- sufficient juveniles.

Sexual reproduction and formation of resting cysts typically occurs during bloom decline. In its dormant stages, P. bahamense develop spherical, double-layered cysts for protection. These cysts, called Polysphaeridium zoharyi in the paleontological classification system, are similar in both P. bahamense varieties and have tubular processes protruding from the outer layer.

Its canal system is of asconoid type. The colony consists of few simple vase-like, cylindrical individuals each terminating in an osculum and united at their bases by irregular horizontal tubes. Leucosolenia reproduces both asexually and sexually. asexual reproduction by budding and sexual reproduction takes place by formation of gametes, i.e.

Statue as a university student in Lund Rothman showed Linnaeus that botany was a serious subject. He taught Linnaeus to classify plants according to Tournefort's system. Linnaeus was also taught about the sexual reproduction of plants, according to Sébastien Vaillant. In 1727, Linnaeus, age 21, enrolled in Lund University in Skåne.

The process in which the two gametes from the two parents unite is called fertilization. Half of the genetic information from both parents is combined. This results in offspring that are genetically different from each other and from the parents. In short, sexual reproduction allows a continuous rearrangement of genes.

Protists are a large group of diverse eukaryotic microorganisms, mainly unicellular animals and plants, that do not form tissues. Eukaryotes emerged in evolution more than 1.5 billion years ago. The earliest eukaryotes were likely protists. Mating and sexual reproduction are widespread among extant eukaryotes including protists such as Paramecium and Chlamydomonas.

Unusually among vertebrates, the ginbuna species has two different reproductive modes. The diploid form practices the usual sexual reproduction. However, the triploid and rare tetraploid forms practice a type of asexual reproduction known as gynogenesis, in which the sperm contributes no genetic material, but its presence is required for egg development.

There, sexual reproduction will occur and oocysts will be created and passed through the feces.Dogs are often the definitive host but can act as an intermediate host as well. Cows are usually the intermediate host. No horizontal cow-to-cow transmission have been shown, although salival interactions have been suggested.

However, sexual reproduction involving meiosis is also a primitive characteristic of eukaryotes.Bernstein, H., Bernstein, C. Evolutionary origin and adaptive function of meiosis. In “Meiosis”, Intech Publ (Carol Bernstein and Harris Bernstein editors), Chapter 3: 41-75 (2013). Thus meiosis and mitosis may both have evolved, in parallel, from ancestral prokaryotic processes.

Sperm centrioles are important for 2 functions:Avidor-Reiss, T., Khire, A., Fishman, E. L., & Jo, K. H. (2015). Atypical centrioles during sexual reproduction. Frontiers in cell and developmental biology, 3, 21. Chicago (1) to form the sperm flagellum and sperm movement and (2) for the development of the embryo after fertilization.

An information theoretic analysis using a simplified but useful model shows that in asexual reproduction, the information gain per generation of a species is limited to 1 bit per generation, while in sexual reproduction, the information gain is bounded by where G is the size of the genome in bits.

Mating structures P. ramorum is heterothallic and has two mating types, A1 and A2, required for sexual reproduction. The European population is predominantly A1 while both mating types A1 and A2 are found in North America. Genetics of the two isolates indicate that they are reproductively isolated.Ivors, K., et al.

In the 1980s, DNA analyses of the developmental stages of T. brucei started to indicate that the trypomastigote in the tsetse fly undergoes meiosis, i.e. a sexual reproduction stage. But it is not always necessary for a complete life cycle. The existence of meiosis-specific proteins was reported in 2011.

During sexual reproduction, mating with a close relative (inbreeding) often leads to inbreeding depression. Inbreeding depression is considered to be largely due to expression of deleterious recessive mutations. The effects of inbreeding have been studied in many vertebrate species. In several species of fish, inbreeding was found to decrease reproductive success.

In 1889, Schroeter created the genus Urophlyctis for those species with epibiotic, ephemeral zoosporangia and sexually derived resting spores. He placed both in the same subfamily as Cladochytrium. In 1891, Fischer refuted Schroeter's observations on sexual reproduction and merged Physoderma and Urophlyctis with Cladochytrium. In 1897, Schroeter separated them once more.

The disease is primarily a root rot that causes symptoms of foliar blight. Sporangia are produced on the mycelium and can produce zoospores for asexual reproduction or an oogonium and antheridium for sexual reproduction. Once the oogonium is fertilized, the oospore either infects via germ tube or produces sporangia and zoospores.

Generally, it is unusual for males within a species to be the choosy sex. There are many reasons for this. In humans, following sexual reproduction, the female is obliged to endure a nine-month pregnancy and childbirth. This means that females naturally provide a greater parental investment to offspring, than males.

Genetic Recombination. New York: Wiley; 1982. These studies have proven central to understanding the mechanism of meiotic recombination, which in turn is a key to understanding the adaptive function of sexual reproduction. The use of tetrads in fine-structure genetic analysis is described in the articles Neurospora crassa and Gene conversion.

Like vertebrates, most invertebrates reproduce at least partly through sexual reproduction. They produce specialized reproductive cells that undergo meiosis to produce smaller, motile spermatozoa or larger, non-motile ova. These fuse to form zygotes, which develop into new individuals. Others are capable of asexual reproduction, or sometimes, both methods of reproduction.

Under optimal conditions, ascospores mature and are released to initiate new infections . Conditions necessary for spore maturation differ among species. Asexual reproduction is where the mother fungi and offspring are genetically identical. Powder mildew fungi offspring of wheat and barley species are more successful from asexual reproduction compared to sexual reproduction counterparts.

Tetrahymena conjugation. When nutrients are scarce, two individuals (A) pair with each other and begin sexual reproduction (conjugation). (B) The diploid micronucleus in each individual undergoes meiosis to form four haploid nuclei, and three of these are degraded. (C) The remaining haploid nucleus divides mitotically to form two pronuclei in each cell.

Although most often coinciding, morphological alternation and nuclear phases alternation are sometimes independent of one another, e.g., in many red algae, the same nuclear phase may correspond to two diverse morphological generations. In some ferns which lost sexual reproduction, there is no change in nuclear phase, but the alternation of generations is maintained.

Ridley M (2004) Evolution, 3rd edition. Blackwell Publishing, p. 314. The two-fold cost of sex includes this cost and the fact that any organism can only pass on 50% of its own genes to its offspring. One definite advantage of sexual reproduction is that it impedes the accumulation of genetic mutations.

Amoebidium species are single- celled, cigar-shaped or tubular in vegetative growth form (= thallus), and attach to the exoskeleton of various freshwater arthropod hosts (Crustaecea or Insecta) by means of a secreted, glue-like basal holdfast. The thalli are coenocytic (i.e. lack divisions within the cell) and are unbranched. Sexual reproduction is unknown.

Paramoebidium species are unicellular. The vegetative cells (= thalli) have an elongate, hair-like growth form with a secreted, glue-like holdfast at the base that attaches them to the host digestive tract lining. Sexual reproduction is unknown. During asexual reproduction, the entire content of the cell is partitioned into many motile amoeboid cells.

After reaching adulthood, M. laryngeus migrates upwards to the trachea, larynx, or bronchi, where sexual reproduction occurs. Egg production begins about three weeks later, and eggs are coughed up and expelled in sputum, or excreted in feces. Larvae may hatch from embryonated eggs outside of the mammalian host.Acha PN, Szyfres B. Mammomonogamiasis.

In culture, colonies of U. orissi are yellowish white in colour before darkening to buff or brownish-orange. Colonies are flat, dense and take on a woolly to coarsely powdery texture. U. orissi degrades keratin relatively quickly. U. orissi has a heterothallic mating system, requiring two compatible "sexes" for sexual reproduction to occur.

It is distinguishable from closely related species by its light colored and heart-shaped ascospores used for sexual reproduction. Scopulariopsis candida has been identified as the cause of some invasive infections, often in immunocompromised hosts, but is not considered a common human pathogen. There is concern about amphotericin B resistance in S. candida.

R. oryzae has abundant, root-shaped rhizoids. Zygospores are produced by diploid cells when sexual reproduction occurs under nutrient poor conditions. They have colors that range from red to brown, they are spherical or laterally flattened, and ranges from 60-140μm in size. In high nutrient levels, R. oryzae reproduces asexually, producing azygospores.

Some commonly found Protist pathogens such as Toxoplasma gondii are capable of infecting and undergoing asexual reproduction in a wide variety of animals – which act as secondary or intermediate host – but can undergo sexual reproduction only in the primary or definitive host (for example: felids such as domestic cats in this case).

The haploid phase begins when the mature organism releases many spores, which then germinate to become male or female gametophytes. Sexual reproduction then results in the beginning of the diploid sporophyte stage, which will develop into a mature individual. The parenchymatous thalli are generally covered with a mucilage layer, rather than cuticle.

It is often used to categorize fungi. In yeast, heterothallic cells have mating types a and α. An experienced mother cell (one that has divided at least once) will switch mating type every cell division cycle because of the HO allele. Sexual reproduction commonly occurs in two fundamentally different ways in fungi.

Sexual reproduction in Oedogonium is oogamous; and can be monoecious or dioecious. Species may either be macrandrous (lacking dwarf males) or nannandrous (possessing dwarf males). Dwarf males are small, short, antheridium-producing filaments attached near the oogonia (female sex organ). These dwarf males are derived by repeated cell division of multiflagellate androspores.

A heterokaryon is a multinucleate cell that contains genetically different nuclei. Heterokaryotic and heterokaryosis are derived terms. This is a special type of syncytium. This can occur naturally, such as in the mycelium of fungi during sexual reproduction, or artificially as formed by the experimental fusion of two genetically different cells, as e.g.

This allowed the plant to perform sexual reproduction in its morphologically immature state because the complicated Stylidium-like flowers were not required for pollination.Laurent, N., Bremer, B., and Bremer, K. (1999). Phylogeny and generic interrelationships of the Stylidiaceae (Asterales), with a possible extreme case of floral paedomorphosis. Systematic Botany, 23(3): 289-304.

Given that sexual reproduction is the means by which genes are propagated into future generations, sexual selection plays a large role in human evolution. Human mating, then, is of interest to evolutionary psychologists who aim to investigate evolved mechanisms to attract and secure mates.Wilson, G.D. Love and Instinct. London: Temple Smith, 1981.

The leaves are serrate and very brittle, breaking easily when handled. Reproduction is generally by offsets, which may number five or more per plant. In the UK, male plants have rarely if ever been recorded, although some hermaphrodite flowers have been recorded from more southerly locations. Sexual reproduction is not known to occur.

Males and females do not directly copulate; sexual reproduction involves the male depositing six to eighteen spermatophores onto the substrate in front of the female - if the female is sexually receptive she rubs the ventral (front) surface of her abdomen (her venter) over the spermatophore, and later transfers these to her genital aperture.

Since the emergence of the modern evolutionary synthesis in the 20th century, numerous biologists including W. D. Hamilton, Alexey Kondrashov, George C. Williams, Harris Bernstein, Carol Bernstein, Michael M. Cox, Frederic A. Hopf and Richard E. Michod – have suggested competing explanations for how a vast array of different living species maintain sexual reproduction.

The zygote is then becomes an auxospore, which has no rigid frustule. Inside the auxospore, a large initial cell is produced. Sexual reproduction appears to occur exclusively in the exponential growth phase and be linked to cell density. Sexualization can only be initiated when a species-specific threshold cell concentration is met.

Sperm is formed in spermatic cysts and is free spawned into the surrounding water. Sperm is captured by females and is transported to oocytes within the sponge where fertilization takes place. The occurrence of sexual reproduction peaks from October to November. There is no relationship between age and reproductive ability in S. officinalis.

Elphidium shows dimorphism with alternating generations. The complete cycle for Elphidium crispum takes two years in the shallower marine regions, although it may be delayed at deeper stations. Asexual reproduction reaches a peak in spring of the first year. Sexual reproduction begins early in the second spring as temperatures begin to rise.

Such a colony is called a genet, and an individual in such a population is referred to as a ramet. The colony, rather than the individual, functions as a unit of selection. In other colonial organisms the individuals may be closely related to one another but differ as a result of sexual reproduction.

Giardia had been assumed to be primitively asexual and with no means of transferring DNA between nuclei. These assumptions made it very difficult to explain the remarkably low level of allelic heterozygosity (< 0.01%) in the genome isolate, WB. However, all those assumptions of asexuality are now in doubt, with population genetics providing evidence for recombination and the identification of meiotic genes, evidence for recombination among isolates and the evidence for exchange of genetic material between nuclei during the process of encystation. These findings on sexuality in Giardia, above, have important implications for understanding the origin of sexual reproduction in eukaryotes. Even though sexual reproduction is widespread among extant eukaryotes, it seemed unlikely, until recently, that sex is a primordial and fundamental feature of eukaryotes.

Sexual reproduction does not occur in prokaryotes (organisms without cell nuclei), but they have processes with similar effects such as bacterial conjugation, transformation and transduction, which may have been precursors to sexual reproduction in early eukaryotes. In the production of sex cells in eukaryotes, diploid mother cells divide to produce haploid cells known as gametes in a process called meiosis that involves genetic recombination. The homologous chromosomes pair up so that their DNA sequences are aligned with each other, and this is followed by exchange of genetic information between them. Two rounds of cell division then produce four haploid gametes, each with half the number of chromosomes from each parent cell, but with the genetic information in the parental chromosomes recombined.

The existence of two sexes seems to have been selected independently across different evolutionary lineages (see convergent evolution). The repeated pattern is sexual reproduction in isogamous species with two or more mating types with gametes of identical form and behavior (but different at the molecular level) to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is very much larger than the male and has no ability to move. There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction.. Accordingly, sex is defined across species by the type of gametes produced (i.e.: spermatozoa vs.

In some areas, it dominates the understory. When available, this plant is favored by domestic and wild ungulates, which browse away the aboveground parts. Animals may eat so much plant material that they prevent all sexual reproduction within a population. This is one reason why it was considered to be rare and in decline.

Powdery mildew fungi can only reproduce on their living cell host and reproduce both sexually and asexually. Sexual reproduction is via chasmothecia (formerly cleistothecium), a type of ascocarp where the genetic material recombines. Powdery mildew fungi must be adapted to their hosts to be able to infect them. Within each ascocarp are several asci.

Unlike pulmonate and opistobranch gastropods, tritons are not hermaphrodites; they have separate sexes and undergo sexual reproduction with internal fertilization. The female deposits white capsules in clusters, each of which contains many developing larvae. The larvae emerge free-swimming and enter the plankton, where they drift in open water for up to three months.

Cryptomonad flagella are inserted parallel to one another, and are covered by bipartite hairs called mastigonemes, formed within the endoplasmic reticulum and transported to the cell surface. Small scales may also be present on the flagella and cell body. The mitochondria have flat cristae, and mitosis is open; sexual reproduction has also been reported.

Chlamydomonas has all three types of sexual reproduction. They share many similarities with the higher plants, including the presence of asymmetrical flagellated cells, the breakdown of the nuclear envelope at mitosis, and the presence of phytochromes, flavonoids, and the chemical precursors to the cuticle.Raven, Evert and Eichhorn. The Biology of Plants 7th edition, pg. 335.

Pichia (Hansenula and Hyphopichia are obsolete synonyms) is a genus of yeasts in the family Saccharomycetaceae with spherical, elliptical, or oblong acuminate cells. Pichia is a teleomorph, and forms hat-shaped, hemispherical, or round ascospores during sexual reproduction. The anamorphs of some Pichia species are Candida species. The asexual reproduction is by multilateral budding.

Most are long, with a down-turned head with a single median compound eye, and a carapace covering the apparently unsegmented thorax and abdomen. Most species show cyclical parthenogenesis, where asexual reproduction is occasionally supplemented by sexual reproduction, which produces resting eggs that allow the species to survive harsh conditions and disperse to distant habitats.

The evolution of fertilisation is related to the origin of meiosis, as both are part of sexual reproduction, originated in eukaryotes. There are two conflicting theories on how the couple meiosis–fertilisation arose. One is that it evolved from prokaryotic sex (bacterial recombination) as eukaryotes evolved from prokaryotes. The other is that mitosis originated meiosis.

Root suckers are produced twice a year during autumn and spring growth. Purple wood wattle’s dominant reproductive mode is clonal. Clonal reproduction is favoured in situations where the trade-off between survival and seed production favours survival or if disturbance is preventing flowering and fruiting. Clonality can result in permanent failure of sexual reproduction.

Like most sponges, they are filter feeders; they eat food such as plankton or suspended detritus as it passes them. Very little is known about their behavioral patterns except for their feeding ecology and reproductive biology. Tubes occur in varying colors including lavender, pink, gray, and brown. They reproduce both by asexual and sexual reproduction.

But another important thing to consider is that the individuals with the highest fitness are more likely to find a mate and reproduce. Therefore, the chances of offspring with a higher fitness increases. The Vicar of Bray hypothesis proposes that sexual reproduction is more beneficial than asexual reproduction, despite the cost of time and effort.

The formation of zygospores by two mating gametangia. As previously mentioned, C. bertholletiae grow hyphally and reproduce asexually via branching sporangiophores. Unlike in the case of dimorphic pathogenic fungi, growth of C. bertholletiae is inhibited by cycloheximide. As a member of the Zygomycota, sexual reproduction in C. bertholletiae is through the formation of zygospores.

Normally pollen is moved from one plant to another, but many plants are able to self pollinate. The fertilized ovules produce seeds that are the next generation. Sexual reproduction produces genetically unique offspring, allowing for adaptation. Flowers have specific designs which encourages the transfer of pollen from one plant to another of the same species.

The sporozoites grow and multiply in the liver to become merozoites. These merozoites invade the erythrocytes (RBCs) to form trophozoites, schizonts and gametocytes, during which the symptoms of malaria are produced. In the mosquito, the gametocytes undergo sexual reproduction to a zygote, which turns into ookinete. Ookinete forms oocytes from which sporozoites are formed.

Chlamydomonas is widely distributed in freshwater or damp soil. It is generally found in a habitat rich in ammonium salt. It possesses red eye spots for photosensitivity and reproduces both asexually and sexually. Chlamydomonas's asexual reproduction occurs by zoospores, aplanospores, hypnospores, or a palmella stage, while its sexual reproduction is through isogamy, anisogamy or oogamy.

Consequently, social authority is depicted as ever-lasting and never challenged. There is both a lack of parents and absence of any hint of sexual reproduction within the stories. This is connected to another element missing from them, the depiction of material production. All characters apparently work in the service sector of the economy.

R. Soc. Lond. B 263-193-200. and the effect of adaptation to different levels of CO2. According to one frequently cited theoretical hypothesis, sexual reproduction (in contrast to asexual reproduction) is adaptively maintained in benign environments because it reduces mutational load by combining deleterious mutations from different lines of descent and increases mean fitness.

Among diatoms, reproduction is primarily asexual by binary fission, with each daughter cell receiving one of the parent’s cell’s two frustules. However, this asexual division results in a size reduction. To restore the cell size of a diatom population, sexual reproduction must occur. Vegetative diploid cells undergo meiosis to produce active and passive gametes.

The fungi induce host cell death resulting in progressive decay of infected plant tissue, whence they take nutrients. Sexual reproduction takes place with ascospores produced in apothecia, conidia are the means of asexual reproduction. Sclerotia of plano-convexoid shape are typical. Some species also cause damping off, killing seeds or seedlings during or before germination.

This cnidarian never exhibits a medusa life stage. Sexual reproduction can only be done in the prime temperature range of the species. C. multicornis also reproduces asexually through budding from its polyp form. The asexual reproduction cycle reaches maximum reproduction rates at about 39 days in temperatures on the higher scale of their prime range.

Sempervivium calcareum, the houseleek, is a species of flowering plant in the stonecrop family Crassulaceae, native to the southern Alps in Europe. An evergreen succulent perennial, it has a rosette with thick leaves that store water. The leaves are usually green with reddish-purple tips. This plant reproduces with asexual budding and monocarpic sexual reproduction.

Fruit is a syconium and trees may be either female or hermaphrodite. Hermaphrodite trees are functionally male. The tree is known to pollinated by the wasp Kradibia gestroi, where the female lays eggs in female trees with only short-styles. Besides sexual reproduction, the tree may grow with vegetative means propagated by seed and cuttings.

Gametocytes can then be ingested by another blood-sucking insect where they undergo sexual reproduction in the midgut of the insect to produce oocysts. The oocysts rupture and release numerous sporozoites that invade the salivary gland and serve as a focus of subsequent infection for another host once the insect takes its next blood meal.

For others, the BSC is the preferred definition of species. Many geneticists who work on speciation prefer the BSC because it emphasizes the role of reproductive isolation. It has been argued that the BSC is a natural consequence of the effect of sexual reproduction on the dynamics of natural selection.Hopf, F.A.; Hopf, F.W. (1985).

Skeletonemataceae is a family of diatoms in the order Thalassiosirales. There is currently only one known genera in this family of diatoms known as Skeletonema as reported from diatom.org. Being from the thalassiosirales order means that skeletonemataceae are centric diatoms. The sexual reproduction of oogamous is where reproduction occurs by the union of mobile male and immobile female gametes.

These cells are very large, from 0.2 to 2 millimetres in diameter, and are filled with large buoyant vacuoles. Some may contain symbiotic green algae, but there are no chloroplasts. Instead, they feed on other plankton, and there is usually a special flagellum involved in ingestion. Noctilucales reproduce mainly by fission, but sexual reproduction also occurs.

During high tide, this anemone is highly active, feeding on particles it captures. It is also able to defend itself by shooting stinging cells from openings located on the side of the column. This anemone can reproduce both sexually and by cloning. In sexual reproduction, the gametes are liberated into the water column where fertilisation takes place.

The branches, or podetia, are lined with hyphae on their inner surfaces and are perforated with tiny holes. It and similar species undergo vegetative reproduction in which it clones by physically breaking up and spreading. No sexual reproduction has been observed. The lichen's method of biological dispersal is to have its fragments swept or blown to new locations.

Once the metacercariae have been eaten, they excyst in the intestine of the definitive host where the parasite then develops into an adult. Echinostoma are hermaphrodites. A single adult individual has both male and female reproductive organs, and is capable of self-fertilization. Sexual reproduction of adult Echinostoma in the definitive host leads to the production of unembryonated eggs.

When S. cubensis fuse they form a common calcareous deposit in between them. This results in di- or tri corallites or corals that are made of two or three S. cubensis corals all fused together. The subunits are genetically different as a result of the sexual reproduction but can still fuse together as if they are the same individual.

Plants may either self-pollinate or cross- pollinate. In 2013, flowers dating from the Cretaceous (100 million years before present) were found encased in amber, the oldest evidence of sexual reproduction in a flowering plant. Microscopic images showed tubes growing out of pollen and penetrating the flower's stigma. The pollen was sticky, suggesting it was carried by insects.

Human reproduction is any form of sexual reproduction resulting in human fertilization. It typically involves sexual intercourse between a man and a woman. During sexual intercourse, the interaction between the male and female reproductive systems results in fertilization of the woman's ovum by the man's sperm. These are specialized reproductive cells called gametes, created in a process called meiosis.

The nuclear membrane is present throughout the process and the centrioles are not present, unlike many other eukaryotic organisms. The nuclear membrane only divides when the waist of the organism constricts. In sexual reproduction, the cells of two organisms couple close to their sulci (longitudinal groove). Meiosis occurs, which allows the chromosomes given by the haploid parents to pair.

In colonies of Phaeocystis, the colony skin may provide protection against smaller zooplankton grazers and viruses. While suspected in other species (P. pouchetii and P. antarctica), a haploid-diploid life cycle has only been observed in P. globosa. In this cycle, sexual reproduction is dominant in colony bloom formation/termination, and two types of vegetative reproduction exist.

Sterility is the physiological inability to effect sexual reproduction in a living thing, members of whose kind have been produced sexually. Sterility has a wide range of causes. It may be an inherited trait, as in the mule; or it may be acquired from the environment, for example through physical injury or disease, or by exposure to radiation.

Unlike most diatoms P. tricornutum can grow in the absence of silicon, and it can survive without making silicified frustules. This provides opportunities for experimental exploration of silicon-based nanofabrication in diatoms. Another peculiarity is that during asexual reproduction the frustules do not appear to become smaller. This allows continuous culture without need for sexual reproduction.

Inside the fish, the parasites encyst in the body cavity, the musculature, or other organs. Metacercarial cysts are about 1 mm in diameter and are easily seen as small white colored lumps, sometimes through the skin of live fish. The life cycle is completed when an infected fish is eaten by an eel and where sexual reproduction occurs.

Asexual reproduction can be accomplished by two mechanisms. Split or fission reproduction occurs when the coral splits along its mouth creating a clone. Alternatively, particulates released from the foot can develop into a new specimen, which is called laceration. Sexual reproduction produces a larva called a planula which once on the seabed develops into a new individual.

T. solium eggs can cause cysticercosis in humans. Intermediate hosts, which harbor the disease for a short period of time, include: sheep, horses, cattle, pigs, and deer. Definitive hosts, which harbor the parasite until it reaches maturity and during sexual reproduction, include dogs, foxes, and other canids.Taylor, M.A, Coop, R.L., Wall, R.L. (2007) Veterinary Parasitology Blackwell Publishing.

Flower of Ranunculus glaberrimus The flower is the characteristic structure concerned with sexual reproduction in flowering plants (angiosperms). Flowers vary enormously in their construction (morphology). A "complete" flower, like that of Ranunculus glaberrimus shown in the figure, has a calyx of outer sepals and a corolla of inner petals. The sepals and petals together form the perianth.

143, no. 1, pp. 47–54. As a result of the synaptic mutation and ensuing male sterility the sexual reproduction in the species is significantly depressed The dried roots (goldthread) were commercially marketed in Canada until the 1950s or early 60s, to be steeped into a "tea" and swabbed onto areas affected by thrush (candidiasis) infection.

The genus Neurospora also includes homothallic species in which a single haploid individual carries both mating type loci and can undergo self-fertilization leading to meiosis and sexual reproduction. Neurospora africana is an example of such a species. Additionally, some "Neurospora" species are said pseudohomothallic. They carry both mating types, but in separate nuclei in the same individual.

Yamagishiella is a genus of colonial green algae in the family Volvocaceae.See the NCBI webpage on Yamagishiella. Data extracted from the Yamagishiella differs from Eudorina by its isogamous sexual reproduction, but the vegetative morphology and asexual reproduction characteristics of these two genera (especially Y. unicocca and E. unicocca) are indistinguishable.Nozaki, H. Flagellated Green Algae: Volvocaceae, Yamagishiella.

One way to propagate an avocado seed Seeds and spores can be used for reproduction (through e.g. sowing). Seeds are typically produced from sexual reproduction within a species, because genetic recombination has occurred. A plant grown from seeds may have different characteristics from its parents. Some species produce seeds that require special conditions to germinate, such as cold treatment.

Fragment released from the posterior end of an adult worm. All species of Bipalium are hermaphroditic, but Bipalium kewense has rarely been observed using sexual reproduction as a primary means of reproduction. Asexual fragmentation is the primary means of reproduction in B. kewense in temperate regions. Long specimens usually release body fragments at the posterior end by transverse fission.

The production of aplanospores (autospores) in the second way leads to the development of 16-32 spores in the sporangium. For many years, no sexual structures or observation of sexual reproduction in Trebouxia were observed.Friedl, T., & Rokitta, C. (1997). Species relationships in the lichen alga Trebouxia (Chlorophyta, Trebouxiophyceae): molecular phylogenetic analyses of nuclear-encoded large subunit rRNA gene sequences.

Generalized life cycle of corals via sexual reproduction: Colonies release gametes in clusters (1) which float to the surface (2) then disperse and fertilize eggs (3). Embryos become planulae (4) and can settle onto a surface (5). They then metamorphose into a juvenile polyp (6) which then matures and reproduces asexually to form a colony (7, 8).

Sexual reproduction often takes a lot of effort. Finding a mate can sometimes be an expensive, risky and time consuming process. Courtship, copulation and taking care of the new born offspring may also take up a lot of time and energy. From this point of view, asexual reproduction may seem a lot easier and more efficient.

Pavona cactus can reproduce sexually or asexually. In sexual reproduction, gametes are released into the sea where fertilisation takes place. The egg hatches into a free-swimming planula larva that settles on the seabed when it has completed its development. Here it undergoes metamorphosis to become a coral polyp which buds repeatedly to start a new colony.

Extension publications (MU), 2008. Senescent corn leaves are an important plant part for the growth and development of C. carbonum, because it provides biochemicals required for the formation of perithecia, asci and ascospores.Fries, R.E. and R.R. Nelson, The influence of extracts from senescent corn leaves on sexual reproduction in Cochliobolus carbonum. Canadian Journal of Microbiology, 1972.

The snails are to a certain extent hermaphrodites, but separate sexes exist, and the snails reproduce through sexual reproduction. The female is fertilized by the male internally, and the female responds by depositing fertilized eggs. The egg capsules laid by the female contain multiple embryos. It takes about seven days for the eggs to hatch into larvae.

After conidia are induced to form conidial anastomosis tubes, they grow homing toward each other, and they fuse. Once fusion happens, the nuclei can pass through fused CATs. These are events of fungal vegetative growth and not sexual reproduction. Fusion between these cells seems to be important for some fungi during early stages of colony establishment.

T. reesei QM6a has a MAT1-2 mating type locus. The opposite mating type, MAT1-1, was recently found, proving that T. reesei is a heterothallic species. After being regarded as asexual since its discovery more than 50 years ago, sexual reproduction can now be induced in T. reesei QM6a leading to formation of fertilized stromata and mature ascospores.

The B. muscus hydroid buds and forms medusae by asexual reproduction. When these mature, sexual reproduction occurs, the fertilised eggs settle out and new hydroids are formed. The hydroid grows rapidly and may starts to produce medusae when as little as seven weeks old. The medusae grow on the side branches and become free swimming when they are released.

So, even though asexual whiptail lizards populations lack males, sexual stimuli still increase reproductive success. From an evolutionary standpoint, these females are passing their full genetic code to all of their offspring (rather than the 50% of genes that would be passed in sexual reproduction). Certain species of gecko also reproduce by parthenogenesis. Homosexuality in sexually reproducing lizards.

In A. J. Southward (ed.), 1987. The sessile lifestyle of barnacles makes sexual reproduction difficult, as the organisms cannot leave their shells to mate. To facilitate genetic transfer between isolated individuals, barnacles have extraordinarily long penises⁠. Barnacles probably have the largest penis to body size ratio of the animal kingdom, up to eight times their body length.

For the advantage due to genetic variation, there are three possible reasons this might happen. First, sexual reproduction can combine the effects of two beneficial mutations in the same individual (i.e. sex aids in the spread of advantageous traits). Also, the necessary mutations do not have to have occurred one after another in a single line of descendants.

If a mutation has a deleterious effect, it will then usually be removed from the population by the process of natural selection. Sexual reproduction is believed to be more efficient than asexual reproduction in removing those mutations from the genome. There are two main hypotheses which explain how sex may act to remove deleterious genes from the genome.

Reproduction can be by sexual or asexual means. In sexual reproduction, eggs and sperm are ejected through the mouth and liberated into the sea. The fertilised egg develops into a planula, which settles after fifteen to twenty days and grows into a new individual. In asexual reproduction, fragments of the column are capable of regenerating into new individuals.

During sexual reproduction, hyphae of compatible mating types touch and fuse, ultimately giving rise to a thick- walled zygosporangium containing a single zygospore. Germination from the zygospore leads to growth of new hyphae that give rise to asexual spores of both + and - mating type. Germination of these spores produces new haploid hyphae of the same mating type.

Sexual reproduction occurs by division of each cell of the colony into 16-32 zoogametes. Zoogametes show indications of heterogamy, a slight difference in the size and motility of the pairs that fuse to form the smooth walled zygote.Smith, GM. Phytoplankton of Inland Lakes of Wisconsin, Part I, Wisconsin Geological and Natural History Survey, Madison, WI. (1920).

Microsporum fulvum is classified as a teleomorphic species as it sexually reproduces. This sexual state has been referred to as Arthroderma fulvum. Two mating types have been distinguished for the sexual reproduction of the fungus and are characterized with (+) and (-). The (+) mating type synthesizes the elastase enzyme, where as the (-) mating type is unable to produce the elastase.

These lesions often start out yellow and then turn brown as the leaf starts to undergo necrosis. From here, Peronospora can undergo either asexual reproduction or sexual reproduction. Asexual reproduction occurs when the air outside is moist making for favourable conditions. During asexual reproduction, hyphae on the host plant will form sporangiophores, which will produce conidia.

Burrowing anemones are gonochoric, which is to say that individuals are either male or female. Sexual reproduction occurs through broadcast spawning, where eggs and sperm are released into the sea to achieve fertilization. The releases of gametes appears to be coordinated, and mass spawning events have been observed at low tide. Fertilized eggs become free swimming larva.

Incomplete lineage sorting commonly happens with sexual reproduction because the species cannot be traced back to a single person or breeding pair. When organism tribe populations are large (i.e. thousands) each gene has some diversity and the gene tree consists of other pre-existing lineages. If the population is bigger these ancestral lineages are going to persist longer.

Colonial forms also increase the size of the colony by budding off new individuals to share the same tunic. Pyrosome colonies grow by budding off new zooids near the posterior end of the colony. Sexual reproduction starts within a zooid with an internally fertilized egg. This develops directly into an oozooid without any intervening larval form.

Division of tubers is possible when the plant is dormant in autumn. Vegetative propagation of L tuberosus is very successful and sexual reproduction might only take place for genetic diversifications or to colonize different habitats. The diploid plant has 14 chromosomes. There is a high variation in the percentage of constitutive heterochromatin between different L tuberosus plants.

O. ophiura is an active brittle star, moving with a jerky swimming action of its legs and sometimes burrowing. It is a filter feeder, feeding on a wide range of food, but also a bottom- feeding carnivore and detritivore. It can regenerate its arms if they are damaged or torn off. Sexual reproduction takes place during the summer.

These loci contain protein-coding regions for G protein-coupled receptors that sense ligands with varying specificity and signal through Mitogen-activated protein kinase cascades, as well as peptide pheromones and transcription factors involved in mate sensation, selection and reproduction.Heitman, Joseph, Sheng Sun, and Timothy Y. James. "Evolution of fungal sexual reproduction." Mycologia 105.1 (2013): 1-27.

The order contains one family (Erysiphaceae), 28 genera and approximately 100 species. Many imperfect fungi (fungi whose sexual reproduction is unknown) belong here, especially the genus Oidium. Recent molecular data have revealed the existence of six main evolutionary lineages. Clade 1 consists of Erysiphe, Microsphaera, and Uncinula, all of which have an Oidium subgenus Pseudoidium mitosporic state.

Frontiers in Neuroscience, 13: 141. . Choanoflagellates grow vegetatively, with multiple species undergoing longitudinal fission; however, the reproductive life cycle of choanoflagellates remains to be elucidated. A paper released in August 2017 showed that environmental changes, including the presence of certain bacteria, trigger the swarming and subsequent sexual reproduction of choanoflagellates. The ploidy level is unknown;Claus Nielsen.

This ploidy shift coincides with mating during which small, flagellated cells fuse with larger flagellated cells. There is also evidence of historical mating and recombination in S. rosetta. S. rosetta is induced to undergo sexual reproduction by the marine bacterium Vibrio fischeri. A single V. fischeri protein, EroS fully recapitulates the aphrodisiac-like activity of live V. fisheri.

Phyllostachys edulis spreads using both asexual and sexual reproduction. The most common and well known mode for this plant is asexual reproduction. This occurs when the plant sends up new culms from underground rhizomes. The culms grow quickly and reach a height of 90 ft or more (depending on the age and health of the plant).

Since a mean of 13 tracts are transferred, the average total of transferred DNA per genome is 575kb. This process is referred to as "Distributive conjugal transfer." Gray et al. found substantial blending of the parental genomes as a result of conjugation and regarded this blending as reminiscent of that seen in the meiotic products of sexual reproduction.

Seeds serve several functions for the plants that produce them. Key among these functions are nourishment of the embryo, dispersal to a new location, and dormancy during unfavorable conditions. Seeds fundamentally are means of reproduction, and most seeds are the product of sexual reproduction which produces a remixing of genetic material and phenotype variability on which natural selection acts.

Inside the tick, the merozoite undergoes sexual reproduction (gamogony), which is followed by asexual reproduction, resulting in many sporozoites. These are found in the tick salivary glands, and they move from there into the next dog on which the tick feeds. Pregnant dogs can transmit B. canis to their unborn puppies, so infected females should not be bred.

Once fusion occurs, the respective nuclei can pass through the fused CATs from one conidium to the other. These are events of fungal vegetative growth (asexual reproduction) and not sexual reproduction. Part of the CAT fusion (cell fusion) have been shown to be a coordinated behaviour.Fleissner, A.; Leeder, A.; Roca M., M.G.; Read, N.D.; Glass, N.L. (2009).

Euglenoids have not been observed to undergo sexual reproduction; however, asexual reproduction does occur through mitosis followed by cytokinesis. Esson, H. J.; Leander, B. S. (2006). “A model for the morphogenesis of strip reduction patterns in phototrophic euglenids: Evidence for heterochrony in pellicle evolution”. Evolution Development, 8 (4): 378-388. doi:10.1111/j.1525-142x.2006.00110.

Kimball, J.W. (2006) "Sexual Reproduction in Humans: Copulation and Fertilization," Kimball's Biology Pages (based on Biology, 6th ed., 1996) Instead, paternal mitochondria are marked with ubiquitin to select them for later destruction inside the embryo. Discussed in Science News. The egg cell contains relatively few mitochondria, but it is these mitochondria that survive and divide to populate the cells of the adult organism.

Queen ants of the species C. cursor can produce female reproductive progeny (i.e. potential new queens or gynes) by parthenogenesis. Parthenogenesis, in this case, involves, a process (automictic thelytoky) by which two haploid products of meiosis fuse to form a diploid zygote that develops into a gyne. Queens can also produce female worker ants by sexual reproduction involving fertilisation of eggs.

The male is similarly transparent. The abdomen is elongated, but the carapace is small and only covers the brood pouch. The six pairs of thoracic appendages form a "feeding basket" which is used to capture prey. The second antennae are used for swimming, while the first antennae are rudimentary in females but elongated in males, where they are used in sexual reproduction.

The recently available Acanthamoeba genome sequence revealed several orthologs of genes employed in meiosis of sexual eukaryotes. These genes included Spo11, Mre11, Rad50, Rad51, Rad52, Mnd1, Dmc1, Msh and Mlh. This finding suggests that Acanthamoeba is capable of some form of meiosis and may be able to undergo sexual reproduction. In sexually reproducing eukaryotes, homologous recombination (HR) ordinarily occurs during meiosis.

New haploid gametes are formed during meiosis and develop into spores. The adaptive basis for the maintenance of sexual reproduction in the Ascomycota and Basidiomycota (dikaryon) fungi was reviewed by Wallen and Perlin. They concluded that the most plausible reason for maintaining this capability is the benefit of repairing DNA damage, caused by a variety of stresses, through recombination that occurs during meiosis.

With the exception of Palmophyllophyceae, Trebouxiophyceae, Ulvophyceae and Chlorophyceae, which show various degrees of multicellularity, all the Chlorophyta lineages are unicellular. Some members of the group form symbiotic relationships with protozoa, sponges, and cnidarians. Others form symbiotic relationships with fungi to form lichens, but the majority of species are free-living. Some conduct sexual reproduction, which is oogamous or isogamous.

Although fertile plants are not unknown, mature plants bearing spore capsules are rarely found. It is therefore assumed that Ricciocarpos spreads primarily through vegetative reproduction as the plants break apart. It has been suggested that the aquatic forms remain sterile and that sexual reproduction is largely limited to terrestrial forms, but other sources maintain that terrestrial forms are normally sterile as well.

Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents. Through heredity, variations between individuals can accumulate and cause species to evolve by natural selection. The study of heredity in biology is genetics.

Thesprotia graminis, common name American grass mantis or grass-like mantis, is a species of praying mantis native to the Southern United States.Thesprotia graminis It is found in Florida and Georgia.Dichotomous Key to Species of Mantids that may occur in FloridaBugs in Cyberspace This species can reproduce parthenogenetically or through sexual reproduction. T. graminis is similar in appearance to Brunneria borealis.

Hybridogenesis is a hemiclonal mode of reproduction — half of a hybrid genome is transmitted intact clonally from generation to generation (' genome in the L-E system) — not recombined with a parental species genome (L here), while the other half (L) is transmitted sexually — obtained (replaced) each generation by sexual reproduction with a parental species (sexual host, P. lessonae in the L-E system).

It is a means of plant propagation. When propagating plants to increase a stock of a cultivar, thus seeking identical copies of parent plant, various cloning techniques (asexual reproduction) are used. Offsets are a natural means by which plants may be cloned. In contrast, when propagating plants to create new cultivars, sexual reproduction through pollination is used to create seeds.

Genetic variation arises from mutations, from natural selection, migration between populations (gene flow) and from the reshuffling of genes through sexual reproduction. Mutations lead to a change in the DNA structure, as the order of the bases are rearranged. Resultantly, different polypeptide proteins are coded. Some mutations may be positive and can help the individual survive more effectively in their environment.

Most plants are dioicous except for U. phyllantha, which is monoicous. Asexual reproduction is uncommon, except in U. phyllantha, in which asexual propagules can commonly be found at the leaf apex. Sexual reproduction involves the transfer of sperm from the antheridium (plural: antheridia) via water. Drops of water carrying sperm allow for the fertilization of the egg housed within the archegonium (plural: archegonia).

It is not known if P. tricornutum can reproduce sexually. To date no substantial evidence has been found to support sexual reproduction in a laboratory or other setting. Although P. tricornutum can be considered to be an atypical pennate diatom it is one of the main diatom model species. A transformation protocol has been established and RNAi vectors are available.

Eurycantha calcarata typically reproduce through sexual reproduction and produce eggs that hatch 4.5-6.5 months later. When no males are present in the population, this stick insect exhibits parthenogenesis instead. Eggs are typically 8.2 mm and 4 mm wide, with a somewhat cylindrical shape. Egg color can vary from shades of brown to grey and surface texture is rough and shiny.

The effects of evolutionary ecology and its consequences can be seen in the case of color variation among African cichlid fish. With over 2,000 species, cichlid fishes are very species-rich and capable of complex social interactions. Polychromatism, the variation of color patterns within a population, occurs within cichlid fishes due to environmental adaptations and to increase chances of sexual reproduction.

Recent evidence indicates that several Amoebozoa lineages undergo meiosis. Orthologs of genes employed in meiosis of sexual eukaryotes have recently been identified in the Acanthamoeba genome. These genes included Spo11, Mre11, Rad50, Rad51, Rad52, Mnd1, Dmc1, Msh and Mlh. This finding suggests that the ‘'Acanthamoeba'’ are capable of some form of meiosis and may be able to undergo sexual reproduction.

Propagation is normally vegetative from small fragments which grow into new individuals. Under certain conditions sexual reproduction occurs in a process called holocarpy. Almost all of the cytoplasm in the thallus is converted into biflagellate gametes, which are discharged into the sea through papillae. After fertilisation, the zygote becomes a protonema and this in turn develops into a new thallus.

In earthworms, the clitellum can only be seen when the worm is sexually mature. It may be white, orange-red or reddish-brown in colour. Earthworms are ready to mate when their clitellum is orange. In leeches, the clitellum appears during mating season, where it is used for both sexual reproduction and the secretion of a cocoon for the eggs.

Autumn lady's tresses spreads primarily through sexual reproduction. However, the plants to a limited extent also propagate vegetatively by the formation of side buds on the underground stem. The new plant forms its own tuber and leaf rosette, and if the old root dies, the connection between the two daughter plants is broken. The plants therefore often occur in small dense groups.

One of these is an LEA protein, which has a protective function that prevents other proteins from agglutinating during the desiccation process; the other one helps to maintain the cell membrane. This gives bdelloid rotifers a means of becoming genetically diverse even though not exchanging genes through sexual reproduction and suggests that asexual reproduction could even be an evolutionary means of creating diversity.

Central fusion and terminal fusion automixis The process of automictic thelytoky with central fusion has been studied in C. cursor. Central fusion allows heterozygosity to be largely maintained. Queen ants use this process to produce female reproductive progeny (gynes), thus increasing the transmission of their own genes through the germline lineage. Also, queens use sexual reproduction to produce worker ants.

Both species reproduce asexually by binary fission to make identical copies of itself[1]. Speculations of sexual dimorphism that is the difference between the female and male counterparts have allowed researchers to draw conclusion that species of this genus can undergo sexual reproduction[1]. The first record of DSP with Dinophysis acuminata and Dinophysis fortii was in 1980 in the Patagonian coast[4].

The trophozoites can mature into schizonts and release more merozoites into the circulatory system, or they can differentiate into still haploid gametocytes. The gametocyte is the sexual stage of the life cycle, with female macrogametocytes and male microgametocytes. Sexual reproduction does not occur in the human host. Instead, the gametocytes only fuse to form a diploid zygote when ingested by the female Anopheles.

G. candidum is thought to be homothallic but most isolates are self-sterile. Sexual reproduction was first observed in strains isolated from soils in Puerto Rico. The fungus produces globose asci that contain a single, thick walled, uninucleated, globose to oval ascospore measuring 6–7 μm by 7–10 μm. The ascospores have a smooth inner wall and a furrowed outer wall.

Coccolithophores reproduce asexually through binary fission. In this process the coccoliths from the parent cell are divided between the two daughter cells. There have been suggestions stating the possible presence of a sexual reproduction process due to the diploid stages of the coccolithophores, but this process has never been observed. K or r- selected strategies of coccolithophores depend on their life cycle stage.

The purpose of sexual reproduction is unclear, as in many organisms it has a 50% cost (fitness disadvantage) in relation to asexual reproduction.Ridley M (2004) Evolution, 3rd edition. Blackwell Publishing, p. 314. Mating types (types of gametes, according to their compatibility) may have arisen as a result of anisogamy (gamete dimorphism), or the male and female genders may have evolved before anisogamy.

Because investment in flowers and seed production can be costly for alpine plants, they often use clonal propagation. This strategy becomes increasingly more frequent as altitude increases, and is most common among cryptogams and grasses. Some alpine plants use it as their predominant method of reproduction. In these plants, sexual reproduction is rare and does not contribute significantly to reproductive output.

This fourth circuit is imprinted by the first orgasm-mating experiences and tribal "morals". It is concerned with sexual pleasure (instead of sexual reproduction), local definitions of "moral" and "immoral", reproduction, rearing of the young, etc. The fourth circuit concerns itself with cultural values and operating within social networks. This circuit is said to have first appeared with the development of tribes.

Unlike most common lore and portrayals, werewolves do not change completely into a beast. In Supernatural, werewolves can be created both through being bitten and through sexual reproduction. Supernatural features two types: regular werewolves and pureblood werewolves. Regular werewolves are the type that the Winchesters hunted in their earlier years while purebloods are the type featured in the later seasons of the show.

In some plants, a leaf section or a portion of root can be used. In sexual reproduction, a propagule is a seed or spore. In micropropagation, a type of asexual reproduction, any part of the plant may be used, though it is usually a highly meristematic part such as root and stem ends or buds.Hartmann and Kester's Plant Propagation, Seventh Edition.

These provide much of the organic carbon needed by the fire coral. The reproduction of fire corals is complex and involves an alternation of asexual and sexual generations. The encrusting parts of the coral expand by the growth of stolons, and the edges of blades expand by sympodial growth. Sexual reproduction involves a sessile polyploid stage and the budding off of planktonic medusae.

Sexually reproducing species are expected to have lower genetic loads. This is one hypothesis for the evolutionary advantage of sexual reproduction. Purging of deleterious mutations in sexual populations is facilitated by synergistic epistasis among deleterious mutations. High load can lead to a small population size, which in turn increases the accumulation of mutation load, culminating in extinction via mutational meltdown.

They are used by ghost crabs for communication. Both exophthalmy and stridulating ridges, however, can not be reliably used to determine phylogenetic relationships between different species of ghost crabs. Sakai & Türkay (2013) regarded the shape of the gonopods as more suited for this. As gonopods are important in sexual reproduction, they are less likely to evolve randomly in response to the environment.

The macronucleus serves the organism's needs, whereas the micronucleus is used for sexual reproduction with exchange of genetic material. Slime molds syncitia form from individual amoeboid cells, like syncitial tissues of some multicellular organisms, not the other way round. To be deemed valid, this theory needs a demonstrable example and mechanism of generation of a multicellular organism from a pre-existing syncytium.

In order to germinate, the seeds require a dormancy period of at least a year. As with other Opuntia species, mechanical or chemical scarification does not seem to help. The species can reproduce either vegetatively or by seed. In fact, the nature of the habitat determines which is more common, with sexual reproduction dominating in grasslands and vegetative propagation dominating in scrublands.

Reproduction in Z. sociatus is mainly asexual although sexual reproduction may happen as well. There is extratentacular budding, which is the creation of a new polyp from an old polyp, and fission, a new fragment in formed. The size of a fragment is also controlled by the increasing rate of mortality with decreasing fragment size. A colony is generally genetically the same.

205x205px Aristotle defined inclination in the first paragraph of Metaphysics with the statement "all men by their nature, desire to know." Thomas Aquinas proposed that humans have four natural inclinations - a natural inclination to preservation (life), an inclination to sexual reproduction (procreation), sociability, and knowledge. Inclination in the modern philosophy of ethics is viewed in the context of morality, or moral worth.

Most members have a complex lifecycle, involving both asexual and sexual reproduction. Typically, a host is infected via an active invasion by the parasites (similar to entosis), which divide to produce sporozoites that enter its cells. Eventually, the cells burst, releasing merozoites, which infect new cells. This may occur several times, until gamonts are produced, forming gametes that fuse to create new cysts.

Prokaryotes (Archaea and Bacteria) reproduce asexually through binary fission, in which the parent organism divides in two to produce two genetically identical daughter organisms. Eukaryotes (such as protists and unicellular fungi) may reproduce in a functionally similar manner by mitosis; most of these are also capable of sexual reproduction. Multiple fission at the cellular level occurs in many protists, e.g. sporozoans and algae.

Micrasterias can produce both asexually and sexually. Asexual reproduction occurs via mitosis. When this occurs the genetic material of Micrasterias is duplicated and two small semi-cells grow between the original semi-cells, gradually increasing in size. Sexual reproduction occurs through a process called conjugation whereby two organisms come together and fuse their haploid cells to form a diploid zygote.

M. Bishop, D. Balding & C. Cannings John Wiley Chichester. Johnson, L.J. and Brookfield, J.F.Y. (2002) Evolutionary dynamics of a selfishly spreading gene that stimulates sexual reproduction in a partially sexual population. J. Evolutionary Biology 15, 42-48. Carr, M., Soloway, J.R., Robinson, T.E. and Brookfield, J.F.Y. (2002) Mechanisms regulating the copy numbers of six LTR retrotransposons in the genome of Drosophila melanogaster.

An asexual colony includes both somatic (vegetative) cells, which do not reproduce, and large, non-motile gonidia in the interior, which produce new colonies through repeated division. In sexual reproduction two types of gametes are produced. Volvox species can be monoecious or dioecious. Male colonies release numerous sperm packets, while in female colonies single cells enlarge to become oogametes, or eggs.

The haploid gametes (daughter cells produced after meiosis) were discovered in 2014. The haploid trypomastigote-like gametes can interact with each other via their flagella and undergo cell fusion (the process is called syngamy). Thus, in addition to binary fission, T. brucei can multiply by sexual reproduction. Trypanosomes belong to the supergroup Excavata and are one of the earliest diverging lineages among eukaryotes.

Heterosis is the tendency for hybrid individuals to exceed their pure bred parents in size and vigor. The phenomenon has long been known in animals and plants. Heterosis appears to be largely due to genetic complementation, that is the masking of deleterious recessive alleles in hybrid individuals. In general, the two fundamental aspects of sexual reproduction in eukaryotes are meiosis, and outcrossing.

The number of mating types depends on the number of genes and the number of alleles for each. Depending of the species, sexual reproduction takes place through gametes or hyphal fusion. When a receptor on one haploid detects a pheromone from a complementary mating type, it approaches the source through chemotropic growth or chemotactic movement if it is a gamete.

The pellets themselves are ejected relatively unchanged. Sexual reproduction takes place in the summer. In a study off the coast of Wales, the worm released sperm in bundles into the water column in May and the ova matured at the same time. The larvae formed part of the zooplankton for a few weeks before undergoing metamorphosis and settling out in June.

Chlamydospores of the yeast Candida albicans Chlamydospores are usually dark-coloured, spherical, and have a smooth (non-ornamented) surface. They are multicellular, with cells connected by pores in the septae between cells. Chlamydospores are a result of asexual reproduction (in which case they are conidia called chlamydoconidia) or sexual reproduction (rare). Teliospores are special kind of chlamydospores formed by rusts and smuts.

The trigger of feeding is understood to be a receptor-mediated response; however, the detail of this process has yet to be established. Sexual reproduction also occurs in the intestine to produce a further round of eggs to complete the cycle. Females are thought to produce a pheromone which attracts males and are able to lay about 10,000 eggs per day.

Similar to other alveolates, the pellicle of Colponema is composed of three membranes and contains inflated cortical alveoli. They also have tubular cristae in their mitochondria. In contrast, the cells do not share important traits that characterize the other groups of alveolates, such as rhoptries, derived ciliature, or palintomy. No resting stages or sexual reproduction has been observed in culture.

Hippospongia communis sexually reproduces year round. The sponge is also hermaphroditic, meaning it has both male and female reproductive organs at the same time. It has been found that during its sexual reproduction, regardless of the location, the Hippospongia communis eggs will fertilize at the same time. The bath sponge reproduction times are all synced throughout different locations that the H. communis inhabit.

Zygote formation is a crucial step in sexual reproduction, and it is reliant on the fusion of sperm and egg cells. Consequently, these cells must be primed to gain fusion-competence. Phosphatidylserine is a phospholipid that usually resides on the inner layer of the cell membrane. After sperm cells are primed, phosphatidylserine can be found on the outer leaflet of the membrane.

Sexual reproduction can be seen as a strategy to survive during times of low nutrients and other unfavorable conditions. H. viridissima has three sexes: female, male, and hermaphrodite. Simultaneous hermaphrodites are dominant during the growing season. It is thought that female gonads need a longer period of inductive conditions for production, that means that there is a scarcity of females in most populations.

Coolia has an asexual and a sexual life cycle. It is thought that under low nutrients, low light, or low temperature conditions, sexual reproduction may be initiated, resulting in the production of a resting cyst. Cells divide asexually by binary fission. The division process begins as the single nucleus with condensed chromosomes elongates and two nuclei develop parallel to each other.

JIC timeline, JIC, retrieved 28 May 2016 She published her findings in 1928.Annals of Applied Biology in November 1928 More mundanely Cayley was interested in slime moulds and she created a better understanding on the sexual reproduction in moulds. Dorothy retired in 1938, and a year later she was the vice president of the British Mycological Society in 1939.

The organism that is the target of an infecting action of a specific infectious agent is called the host. The host harbouring an agent that is in a mature or sexually active stage phase is called the definitive host. The intermediate host comes in contact during the larvae stage. A host can be anything living and can attain to asexual and sexual reproduction.

Hydra budding: When food is plentiful, many Hydra reproduce asexually by budding. The buds form from the body wall, grow into miniature adults and break away when mature. When a hydra is well fed, a new bud can form every two days. When conditions are harsh, often before winter or in poor feeding conditions, sexual reproduction occurs in some Hydra.

In bdelloid rotifers, females reproduce exclusively by parthenogenesis (obligate parthenogenesis),"Bdelloids: No sex for over 40 million years.". TheFreeLibrary. ScienceNews. Retrieved 30 April 2011. while in monogonont rotifers, females can alternate between sexual and asexual reproduction (cyclical parthenogenesis). At least in one normally cyclical parthenogenetic species obligate parthenogenesis can be inherited: a recessive allele leads to loss of sexual reproduction in homozygous offspring.

Although ammonites do occur in exceptional lagerstatten such as the Solnhofen limestone, their soft part record is surprisingly bleak. Beyond a tentative ink sac and possible digestive organs, no soft parts are known at all. They likely bore a radula and beak, a marginal siphuncle, and ten arms. They operated by direct development with sexual reproduction, were carnivorous, and had a crop for food storage.

Detasseling corn (maize) plants from one variety in a field where two varieties are planted. The male flowers are removed so that all seeds are hybrids sired from the second variety. "Open pollination" and "open pollinated" refer to a variety of concepts in the context of the sexual reproduction of plants. Generally speaking, the term refers to plants pollinated naturally by birds, insects, wind, or human hands.

Birth control in the United States has become an arena for conflict between liberal and conservative values, raising questions about family, personal freedom, state intervention, religion in politics, sexual morality and social welfare. Reproductive rights, that is rights relating to sexual reproduction and reproductive health, were first discussed as a subset of human rights at the United Nation's 1968 International Conference on Human Rights.

In some phyla of fungi, the sporangium plays a role in asexual reproduction, and may play an indirect role in sexual reproduction. The sporangium forms on the sporangiophore and contains haploid nuclei and cytoplasm . Spores are formed in the sporangiophore by encasing each haploid nucleus and cytoplasm in a tough outer membrane. During asexual reproduction, these spores are dispersed via wind and germinate into haploid hyphae.

Thomas Hunt Morgan's 1916 illustration of a double crossover between chromosomes. The diploid nature of chromosomes allows for genes on different chromosomes to assort independently or be separated from their homologous pair during sexual reproduction wherein haploid gametes are formed. In this way new combinations of genes can occur in the offspring of a mating pair. Genes on the same chromosome would theoretically never recombine.

It is rarely found in some parts of northeastern North America, particularly in the Great Lakes region. It is an ascomycete or sac fungus, meaning that its microscopic structure utilizes the ascus, a spore- bearing cell, for sexual reproduction. It is a detritivore, and survives on decomposing matter, most commonly leaf litter. It is found in spruce forests and does not currently have any human uses.

Sexual reproduction also takes place. Each zooid is hermaphrodite and fertilisation takes place in the body cavity when a clutch of eggs is fertilised by sperm drawn in with the water stream. The embryos are brooded for a few days before the tadpole-like larvae are expelled into the water column. These quickly settle and cement themselves to suitable surfaces and start new colonies.

Because these two species are descendants of lineages that are highly divergent among eukaryotes, Malik et al. suggested that these meiotic genes were present in a common ancestor of all eukaryotes. Thus, on this view, the earliest ancestor of eukaryotes was likely capable of sexual reproduction. Furthermore, Dacks and Roger proposed, based on phylogenetic analysis, that facultative sex was present in the common ancestor of all eukaryotes.

The first species of Coccidinium that were described were C. legeri and C. duboscquii, found in the cytoplasm of dinoflagellates in brackish waters near Sète, France. They have been noted as lacking photosynthetic stages in their life cycles, which is to be expected given their parasitic nature. Sexual reproduction has been observed “time and again” in C. mesnili as stated by Chatton and Biecheler.

Atriolum robustum feeds on phytoplankton, zooplankton and minute pieces of detritus. Water gets drawn into the zooid through the buccal openings, the edible particles are then filtered out and the water current leaves the zooid through the atrial siphon. Sexual reproduction involves sperm being drawn into the body cavity with the inflowing water current and eggs being fertilised internally. The developing embryos are brooded at first.

As stated above, some members of Blastocladiomycota exhibit alternation of generations. Members of this phylum also exhibit a form of sexual reproduction known as anisogamy. Anisogamy is the fusion of two sexual gametes that differ in morphology, usually size. In Allomyces, the thallus (body) is attached by rhizoids, and has an erect trunk on which reproductive organs are formed at the end of branches.

Sexual reproduction between two populations reduces the genetic distance between the populations. During the Age of Discovery which began in the early 15th century, European explorers sailed all across the globe reaching all the major continents. In the process they came into contact with many populations that had been isolated for thousands of years. The Tasmanian Aboriginals were one of the most isolated groups on the planet.

Sexual reproduction in the Zygnematophyceae takes place through a process called conjugation. Here cells or filaments of opposite gender line up, and tubes form between corresponding cells. The male cells then become amoeboid and crawl across the female, or sometimes both cells crawl into the connecting tube. The cells then meet and fuse to form a zygote, which later undergoes meiosis to produce new cells or filaments.

In certain animals, stressful environments have been known to lead to an increase in gonozooid frequencies. Higher gonozooid frequencies lead to more sexual reproduction and thus more offspring being genetically different from their parents. The resulting higher genetic variance increases the chances of beneficial phenotypes appearing in the population. This beneficial phenotype may in turn spread throughout the population and increase its resistance against the stressing factor.

In organisms with sexual reproduction, incomplete lineage sorting may result in inconsistent phylogenetic trees, depending on which genes are assessed. It is also possible that multiple surviving lineages are generated while interbreeding is still significantly occurring (polytomy). Interbreeding is possible over periods of about 10 million years. Typically speciation occurs over only about 1 million years, which makes it less likely multiple long surviving lineages developed "simultaneously".

The moss Physcomitrella patens has been used as a model organism to study how plants repair damage to their DNA, especially the repair mechanism known as homologous recombination. If the plant cannot repair DNA damage, e.g., double-strand breaks, in their somatic cells, the cells can lose normal functions or die. If this occurs during meiosis (part of sexual reproduction), they could become infertile.

In general, nondisjunction can occur in any form of cell division that involves ordered distribution of chromosomal material. Higher animals have three distinct forms of such cell divisions: Meiosis I and meiosis II are specialized forms of cell division occurring during generation of gametes (eggs and sperm) for sexual reproduction, mitosis is the form of cell division used by all other cells of the body.

Carex utriculata with smut fungus affecting individual seeds The smuts are multicellular fungi characterized by their large numbers of teliospores. The smuts get their name from a Germanic word for dirt because of their dark, thick-walled, and dust-like teliospores. They are mostly Ustilaginomycetes (phylum Basidiomycota) and can cause plant disease. The smuts are grouped with the other basidiomycetes because of their commonalities concerning sexual reproduction.

The genome of Reticulomyxa is repetitive and approximately 320 Mbp in size. The genome contains genes for flagellar components, despite no flagellated form observed. Also, genes coding for proteins associated with meiosis are present in the Reticulomyxa genome but are not actively transcribed. The presence of flagella and meiosis related genes suggests that there is a possibility of sexual reproduction and gamete production in this genus.

Nepanthia belcheri is a hermaphrodite and can reproduce both sexually and asexually. The gonads generally produce oocytes, but in some, no spermatogenic material is present, so they function as ovaries, while others produce sperm and function as testes. Sexual reproduction takes place in October and November. The eggs have large yolk sacs so the larvae are probably lechithotrophic, living on the nutrients already present in the eggs.

Research suggests androgens, such as testosterone, are not sufficient by themselves to prompt sexual motivation in females. In particular, studies with rhesus macaques have observed testosterone was not significantly associated with variations in level of sexual motivation in females. However, some research with nonhuman primates suggests a role for androgens in female sexual reproduction behaviour. Adrenalectomized female rhesus monkeys displayed diminished female sexual receptivity.

If the conditions in the leaf were unfavourable, the mould can undergo sexual reproduction and produce haploid antheridia and haploid oogonia through meiosis. These two structures are the only non-diploid stages of the Hyaloperonospora. The antheridia will fuse to the oogonia inducing plasmogamy followed by karyogamy to form diploid oospores. The oospores will then be dispersed through the wind to infect more plants.

Unlike other cnidarians, Crossota norvegica lives its entire life in the planktonic stage or the planula stage, instead of experiencing both the sessile stage and planula stage. Another unique trait off this species is that it does not develop into a polyp. Polyps typically produce the sexual reproduction gametes of cnidarians by budding. These polyps are stationary and non-moving forms of cnidarians (The Columbia Encyclopedia).

A detailed study found evidence of sexual reproduction in some populations in the Brazilian Amazon. Accordingly, M. smithii consists of a mosaic of sexually and asexually reproducing populations. In asexual populations all ants in a single colony are female clones of the queen. Inside the colony, the ants cultivate a garden of fungus grown with pieces of dead vegetable matter, dead insects, and insect droppings.

Sperm was also found stored in the spermathecas of queens. Sexual reproduction was suggested as a mechanism for maintaining the genetic diversity seen in this species. In summary, M. smithii is not purely asexual, but instead consists of a “mosaic” of sexual and asexual populations. Phylogenetic reconstructions and the biology of the species suggest that these sexual populations gave rise to the asexual ones.

The modern synthesis refers to the merger of genetics with natural selection which occurred in the 1930s and 1940s and offers a reasonably complete framework for understanding the emergence of biological complexity. Although there remain significant gaps in biological knowledge surrounding questions such as the origin of life and the emergence of sexual reproduction, the modern synthesis represents the most complete and well-substantiated joint point.

In water, chlamydospores germinate by producing short germ tubes, each with a sporangium at the tip. Sexual reproduction in Phytophthora palmivora requires the presence of opposite mating types known as A1 and A2. Both A1 and A2 isolates can produce zoospores by selfing when stimulated by sex hormones produced by A2 and A1, respectively. Light is inhibitory to zoospore formation but stimulatory to zoospore germination.

Of the 250 species of aspergilli, about 64% have no known sexual state. However, many of these species likely have an as yet unidentified sexual stage. Sexual reproduction occurs in two fundamentally different ways in fungi. These are outcrossing (in heterothallic fungi) in which two different individuals contribute nuclei, and self- fertilization or selfing (in homothallic fungi) in which both nuclei are derived from the same individual.

Calicium is a genus of leprose lichen lichens. It is in the family Caliciaceae. The genus has a widespread distribution and contains 30 species. The sexual reproduction structures are a mass of loose ascospores that are enclosed by a cup shaped exciple sitting on top of a tiny stalk, having the appearance of a dressmaker's pin (called a mazaedium), hence the common name pin lichen.

Once the intermediate host is eaten by the definitive host, such as a dog or human, the parasite undergoes sexual reproduction within the gut to create macrogamonts and microgamonts. Most definitive hosts do not show any clinical signs or symptoms. Fusion of a macrogamont and a microgamont creates a zygote, which develops into an oocyst. The oocyst is passed through the faeces, completing the lifecycle.

He speculated that they were born of "earth worms", which he believed were formed of mud, growing from the "guts of wet soil" rather than through sexual reproduction. Many centuries passed before scientists were able to demonstrate that such spontaneous generation does not occur in nature. Other early scientists believed that the eelpout Zoarces viviparus was the "mother of eels" (the translation of the German name "Aalmutter").

They can be broken as easily by wind, water flow or animals. Lugwigia Peploides have the ability to double their biomass from their broken particles between 15 and 90 days. This also allows this species to continue to thrive in habitat and regions where sexual reproduction cannot occur. The Ludwigia occur predominantly in wetlands and in the transition areas between aquatic and terrestrial environments.

Their genome is usually a circular bacterial chromosome – a single loop of DNA, although they can also harbor small pieces of DNA called plasmids. These plasmids can be transferred between cells through bacterial conjugation. Bacteria have an enclosing cell wall, which provides strength and rigidity to their cells. They reproduce by binary fission or sometimes by budding, but do not undergo meiotic sexual reproduction.

This is the fundamental basis of the protoplasmic theory of life. De Bary was the first to demonstrate sexuality in fungi. In 1858, he had observed conjugation in the alga Spirogyra, and in 1861, he described sexual reproduction in the fungus Peronospora sp. He saw the necessity of observing the whole life cycle of pathogens and attempted to follow it in the living host plants.

SEM They are covered in silicate scales and spines. In Synura, these are formed on the surface of the chloroplasts, two of which are usually present, but sometimes only one divided into two lobes is seen. The cells have two heterokont flagella, inserted parallel to one another at the anterior, whose ultrastructure is a distinguishing characteristic of the group. Both asexual and isogamous sexual reproduction occur.

Whether sexual reproduction occurs is currently unknown. Collodictyon triciliatum has four flagella connected to basal bodies, generally of equal length, as long as or slightly longer than the body of Collodictyon. Number one flagellum is connected to a dorsal root, while number two flagellum is connected to a ventral root. Number three and four flagella are on either side of these two and have dorsal roots.

In 1970, oocysts were found in (cat) feces. The fecal-oral route of infection via oocysts was demonstrated. In the 1970s and 1980s feces of a vast range of infected animal species was tested to see if it contained oocysts — at least 17 species of felids shed oocysts, but no non-felid has been shown to allow T. gondii sexual reproduction (leading to oocyst shedding).

Yeast, for example, are isogamous sexual organisms which have two mating types which fuse and recombine their haploid genomes. Both sexes reproduce during the haploid and diploid stages of their life cycle and have a 100% chance of passing their genes into their offspring. Some species avoid the 50% cost of sexual reproduction, although they have "sex" (in the sense of genetic recombination). In these species (e.g.

Soon after, Antoine Nicolas Duchesne began to study the breeding of strawberries and made several discoveries crucial to the science of plant breeding, such as the sexual reproduction of strawberry. Later, in the early 1800s, English breeders of strawberry made varieties of F. ananassa which were important in strawberry breeding in Europe, and hundreds of cultivars have since been produced through the breeding of strawberries.

These gametes then fuse to form a zygote, which then develops into an auxospore. Sexual reproduction leads to both an increase in genotypic diversity and the formation of large initial cells through formation of the auxospore. Cells need to be below a species- specific size threshold for the sexual phase to be induced. Many external cues also regulate the initiation, such as day length, irradiance, and temperature.

Decreasing the distance to facilitate contact and/or perception of chemical cues between cells triggers the sexual phase, indicating that high cell density is favorable for sexual reproduction. Additionally, the onset of sexualization is linked to a significant reduction in growth of the vegetative and parental cells, suggesting that vegetative division is inhibited when the two strains of opposite mating type come in contact.

The sporophyte is dependent on the prothallus for nutrition (parasitic) until the embroyo forms its first roots and leaves, whereupon the sporophyte becomes independent and the prothallus subsequently dies. The cycle is complete when spores are produced on the sporophyte. Notably, as in all ferns, water is required for successful sexual reproduction, with the fusion of the gametes entirely dependent on the availability of free water.

Volvox is facultatively sexual and can reproduce both sexually and asexually. In the lab, asexual reproduction is most commonly observed; the relative frequencies of sexual and asexual reproduction in the wild is unknown. The switch from asexual to sexual reproduction can be triggered by environmental conditions and by the production of a sex-inducing pheromone. Desiccation-resistant diploid zygotes are produced following successful fertilization.

The Ectasian Period (from Greek ἔκτασις (éktasis), meaning "extension") is the second geologic period in the Mesoproterozoic Era and lasted from Mya ago to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically. Geologically the name refers to the continued expansion of platform covers during this period. This period is interesting for the first evidence of sexual reproduction.

In the latter case, the daughter may someday become the dominant female, or she may cease to ovulate. Daughters may compete for the role of dominant female with their siblings. Subordinate members do not generally engage in sexual reproduction. All adult black-handed tamarin participate in raising and caring for the young, including non- reproductive members of the group (which may number 2-20 members).

M. histrionica males contain 10,11-epoxy-1-bisabolen-3-ol, a pheromone more commonly known as murgantinol. The stereoisomers of male harlequin bug pheromones consists of two compounds: tridecane and murgantinol. These substances, found specifically in male pheromones, are responsible for aggregation of the insects to aid in sexual reproduction and can also be used in warning predators. A study conducted by Zahn et al.

Each amoebula secretes the proloculum, formsrhizopodia, then it grows and forms other chambers of the shell to become a megalospheric forms. The megalospheric form reproduces sexually by syngamy or conjugation. During sexual reproduction in megalospheric forms, nucleus first breaks up into many small nuclei and the cytoplasm collects around each of these nuclei. The nuclei divide twice giving rise to a large haploid and known as isogametes.

Mutations to the genes are the only source of genetic variation. In sexual reproduction, each parent contributes half of his or her genome to the offspring; thus the offspring contain a mixture of genetic material. Adaptations are traits that increase fitness, the driving force for natural selection. The level of fitness associated with an allele can only be ascertained by comparison with alternate alleles.

These rhizoids can bear intercalary cells, which many be once or twice septate (and what Schroeter saw as evidence of sexual reproduction). The endobiotic thallus gives rise to large, thick-walled, dark-colored resting spores that take the shape of the host cell. It appears the resting spores are formed from the intercalary cells. These resting spores will over winter and germinate in the spring.

Janzen's early work focused on the careful and meticulous documentation of species in Costa Rica, and in particular on ecological processes and the dynamics and evolution of animal-plant interactions. In 1967, for example he described the phenological specialization of bee-pollinated species of Bignoniaceae,Janzen, D. H. 1967. Synchronization of sexual reproduction of trees within the dry season in Central America. Evolution 21: 620-637.

Oomycota or oomycetes () form a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms. They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the result of contact between hyphae of male antheridia and female oogonia; these spores can overwinter and are known as resting spores. Asexual reproduction involves the formation of chlamydospores and sporangia, producing motile zoospores.

R. glutinis is an aerobic yeast characterized by pink, smooth colonies with a moist appearance. Reproduction is typically by multipolar budding although pseudohyphae are occasionally produced. Sexual reproduction is by basidiospores arising from a teliospore developed from a mycelial clamp connection. A distinguishing feature of the species and its close relatives are the intense yellow and red pigments produced during growth on most substrates.

The soybean aphid possesses a heteroecious holocyclic life cycle, which means the insect alternates hosts and undergoes sexual reproduction for at least part of its life cycle. Soybean aphids overwinter as eggs on their primary hosts, buckthorn (Rhamnus spp.). Eggs can be located near buds or within crevices of branches. With a mean supercooling point of , eggs are well-adapted for surviving cold winters.

Arturia canariensis is a filter feeder, sieving plankton and other organic material out of the current of water as it passes through the ostia. Both asexual reproduction by budding and sexual reproduction take place in Arturia canariensis. As in other species, each sponge is a hermaphrodite. Sperm is liberated into the sea and some is drawn into other sponges with the water current that passes through them.

On the other hand, bacterial transformation is clearly an adaptation for transfer of DNA between bacteria of the same species. Bacterial transformation is a complex process involving the products of numerous bacterial genes and can be regarded as a bacterial form of sex. This process occurs naturally in at least 67 prokaryotic species (in seven different phyla). Sexual reproduction in eukaryotes may have evolved from bacterial transformation.

Obligate parthenogenesis is the process in which organisms exclusively reproduce through asexual means.Stelzer C-P, Schmidt J, Wiedlroither A, Riss S (2010) Loss of Sexual Reproduction and Dwarfing in a Small Metazoan. PLoS. Many species have been shown to transition to obligate parthenogenesis over evolutionary time. Well documented transitions to obligate parthenogenesis have been found in numerous metazoan taxa, albeit through highly diverse mechanisms.

Close-up of a flower of Schlumbergera (Christmas or Holiday Cactus), showing part of the gynoecium (the stigma and part of the style is visible) and the stamens that surround it Plant reproductive morphology is the study of the physical form and structure (the morphology) of those parts of plants directly or indirectly concerned with sexual reproduction. Among all living organisms, flowers, which are the reproductive structures of angiosperms, are the most varied physically and show a correspondingly great diversity in methods of reproduction. Plants that are not flowering plants (green algae, mosses, liverworts, hornworts, ferns and gymnosperms such as conifers) also have complex interplays between morphological adaptation and environmental factors in their sexual reproduction. The breeding system, or how the sperm from one plant fertilizes the ovum of another, depends on the reproductive morphology, and is the single most important determinant of the genetic structure of nonclonal plant populations.

If so, sexual recombination of genes will reduce the harm that bad mutations do to offspring and at the same time eliminate some bad mutations from the gene pool by isolating them in individuals that perish quickly because they have an above-average number of bad mutations. However, the evidence suggests that the DMH's assumptions are shaky because many species have on average less than one harmful mutation per individual and no species that has been investigated shows evidence of synergy between harmful mutations. (Further criticisms of this hypothesis are discussed in the article Evolution of sexual reproduction#Removal of deleterious genes) The random nature of recombination causes the relative abundance of alternative traits to vary from one generation to another. This genetic drift is insufficient on its own to make sexual reproduction advantageous, but a combination of genetic drift and natural selection may be sufficient.

Castrated people are sterile, because the testes (for males) and ovaries (for females) produce sex cells needed for sexual reproduction. Once removed, the subject is infertile. The voice does not change considerably. Some castrated people report mood changes, such as depression or a more serene outlook on life, although this might not be due to chemical changes but instead emotional changes due to the implications of the procedure.

This was a discovery of fundamental importance; the conjugation of zoospores was regarded by Pringsheim, with good reason, as the primitive form of sexual reproduction. A work on the course of morphological differentiation in the Sphacelariaceae (1873), a family of marine algae, is of great interest, inasmuch as it treats of evolutionary questions; the authors point of view is that of Karl Wilhelm von Nägeli (1817-1891) rather than Darwin.

However, the majority of C. sowerbii populations existing in the United States are either all male or all female, so there is no sexual reproduction in those populations. During the cold winter months, polyps contract and enter dormancy as resting bodies called podocysts. It is believed that podocysts are transported by aquatic plants or animals to other bodies of water. Once conditions become favorable, they develop into polyps again.

Coccidia can infect all mammals, some birds, some fish, some reptiles, and some amphibians. Most species of coccidia are species-specific in their host. An exception is Toxoplasma gondii, which can infect all mammals, although it can only undergo sexual reproduction in cats. Depending on the species of coccidia, infection can cause fever, vomiting, diarrhea, muscle pain, and nervous system effects and changes to behavior, and may lead to death.

The roots can account for up to 40% of total plant biomass. Kudzu's primary method of reproduction is asexual vegetative spread (cloning) which is aided by the ability to root wherever a stem is exposed to soil. For sexual reproduction, kudzu is entirely dependent on pollinators. Although kudzu prefers forest regrowth and edge habitats with high sun exposure, the plant can survive in full sun or partial shade.

Gynogenetic species, "gynogens" for short, are unisexual, meaning they must mate with males from a closely related bisexual species that normally reproduces sexually. It’s a disadvantageous mating system for males, as they are unable to pass on their DNA. The question as to why this reproductive mode exists, given that it appears to combine the disadvantages of both asexual and sexual reproduction, remains unsolved in the field of evolutionary biology.

Sexual reproduction involves the mixing of genes from two individuals. According to Mendel's Law of Segregation, alleles in a sexually reproducing organism have a 50% chance of being passed from parent to offspring. Meiosis is therefore sometimes referred to as "fair". Highly self- fertilizing or asexual genomes are expected to experience less conflict between selfish genetic elements and the rest of the host genome than outcrossing sexual genomes.

The Placozoa normally propagate asexually, dividing in the middle to produce two (or sometimes, three) roughly equal-sized daughters. These remain loosely connected for a while after fission. More rarely, budding processes are observed: spherules of cells separate from the dorsal surface; each of these combines all known cell types and subsequently grows into an individual of its own. Sexual reproduction is thought to be triggered by excessive population density.

Urticina crassicornis produces by both asexual and sexual reproduction. In the Atlantic populations, eggs and sperm are held and fertilized within the body column. The young are brooded between the mesenteries of the body and are emitted as smallish, well developed, young anemones. Spawning occurs in the spring amongst Puget Sound populations, when eggs (yolky, 0.7 mm in diameter) and sperm are released into the sea for fertilization.

The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Introduction to the Reproductive System, Epidemiology and End Results (SEER) Program. Unlike most organ systems, the sexes of differentiated species often have significant differences.

In contrast to the sexual cycle, in the parasexual cycle recombination takes place during mitosis followed by haploidization (but without meiosis). The recombined haploid nuclei appear among vegetative cells, which differ genetically from those of the parent mycelium. Both heterokaryosis and the parasexual cycle are very important for those fungi that have no sexual reproduction. Those cycles provide for somatic variation in the vegetative phase of their life cycles.

There is no sexual reproduction observed in the euglenoids; however, asexual reproduction can occur through mitosis followed by cytokinesis, where basal bodies and flagellar systems replicate first, followed by the feeding system. Esson, H. J.; Leander, B. S. (2006). “A model for the morphogenesis of strip reduction patterns in phototrophic euglenids: Evidence for heterochrony in pellicle evolution”. Evolution Development, 8 (4): 378-388. doi:10.1111/j.1525-142x.2006.00110.

Latin American Journal of Media Education. 31(1): 155-176 The twist in the tale is that premarital sex is largely prohibited while media coverage of such issues as sexual and reproductive health is considered taboo. This indicates a society characterized by self-denial and hypocrisy because people know and even think that sexual reproduction health is crucial but nobody wants to confront it (Saleh, 2009).Saleh, I., (2009).

Currently, two existing hypotheses may help aid medical diagnostics, especially in endemic areas such as the tropics, the Caribbean, and Brazil. Hypothesis #1: Infection initially begins by the ingestion of foods, water, or intermediate hosts contaminated by adult worms. The infective adults migrate to the larynx or trachea and attach to the mucosal walls. Sexual reproduction occurs here, and the females begin to lay eggs in the upper respiratory region.

As the snails can reproduce both sexually and asexually, the snail has been used as a model organism for studying the costs and benefits of sexual reproduction. Asexual reproduction allows all members of a population to produce offspring and avoids the costs involved in finding mates. However, asexual offspring are clonal, so lack variation. This makes them susceptible to parasites, as the entire clonal population has the same resistance mechanisms.

Cultivated bananas are parthenocarpic and reproduce through conventional vegetative reproduction rather than through sexual reproduction. Development of disease resistance depends on mutations occurring in the propagation units, and hence evolves more slowly than in seed-propagated crops. The development of resistant varieties has therefore been the only alternative to protect the fruit trees from tropical and subtropical diseases like bacterial wilt and Fusarium wilt, commonly known as Panama disease.

The biology of T. vaginalis has implications for understanding the origin of sexual reproduction in eukaryotes. T. vaginalis is not known to undergo meiosis, a key stage of the eukaryotic sexual cycle. However, when Malik et al. examined T. vaginalis for the presence of 29 genes known to function in meiosis, they found 27 such genes, including eight of nine genes that are specific to meiosis in model organisms.

Venturia effusa commonly reproduces asexually via conidia, but it may also produce a teleomorph stage like other Dothideomycetes in which pseudothecia carrying asci and sexual ascospores grow out of the hyphae. This allows for sexual reproduction and genetic recombination of the pathogen. The teleomorph stage, however, is very rare and literature on its characteristics are lacking. The severity of infection depends in part on the timing of inoculation.

As a result, after each division cycle, the average size of diatom cells in the population gets smaller. Once such cells reach a certain minimum size, rather than simply divide, they reverse this decline by forming an auxospore. This expands in size to give rise to a much larger cell, which then returns to size- diminishing divisions. Auxospore production is almost always linked to meiosis and sexual reproduction.

The clitellum is part of the reproductive system of clitellates, a subgroup of annelids which contains oligochaetes (earthworms) and hirudineans (leeches). The clitellum is a thick, saddle-like ring found in the epidermis (skin) of the worm, usually with a light-colored pigment. To form a cocoon for its eggs, the clitellum secretes a viscous fluid. This organ is used in sexual reproduction of some annelids , such as leeches .

Sponges in temperate regions live for at most a few years, but some tropical species and perhaps some deep-ocean ones may live for 200 years or more. Some calcified demosponges grow by only per year and, if that rate is constant, specimens wide must be about 5,000 years old. Some sponges start sexual reproduction when only a few weeks old, while others wait until they are several years old.

Stained human sperm Human spermatozoa Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. However, multiple mates for a female means each individual male has decreased chances of producing offspring.

Polykrikos kofoidii is a species of phagotrophic marine pseudocolonial dinoflagellates that can capture and engulf other protist prey, including the toxic dinoflagellate, Alexandrium tamarense. P. kofoidii is of scientific interest due to its status as a predator of other dinoflagellates, a behavior that is significant in the control of algal blooms. It has a complex life cycle of both vegetative (asexual) and sexual reproduction complicated by its pseudocolonial structure.

Heterothallic species have sexes that reside in different individuals. The term is applied particularly to distinguish heterothallic fungi, which require two compatible partners to produce sexual spores, from homothallic ones, which are capable of sexual reproduction from a single organism. In heterothallic fungi, two different individuals contribute nuclei to form a zygote. Examples of heterothallism are included for Saccharomyces cerevisiae, Aspergillus fumigatus, Aspergillus flavus, Penicillium marneffei and Neurospora crassa.

Each of the species in a pest species complex has to be investigated separately from the others. Species boundaries also define the limits to the spread of insecticide resistance or any genetically controlled traits that are inherited through sexual reproduction. The host relationships and ecology of each of the species within "F. schultzei" also need to be assessed separately before the evolution of this complex can be understood.

Reproduction in the genus Tetraspora can be both sexual and asexual. Sexual reproduction occurs through isogamous means, but occasionally depending on the species, it can also be isogamous or oogamous. Asexual division in Tetraspora occurs via mitotic division; the products can be two or four uninucleate daughter cells. In addition to vegetative cells, asexual reproduction can also produce zoospores, which may act as autospores ranging from two to eight per cell.

If this incorporation occurred only once in four billion years or is otherwise unlikely, then life on most planets remains simple.Lane, 2012 An alternative view is that mitochondria evolution was environmentally triggered, and that mitochondria-containing organisms appeared soon after the first traces of atmospheric oxygen.Martin, W. & Mentel, M. (2010)The Origin of Mitochondria. Nature Education 3(9):58 The evolution and persistence of sexual reproduction is another mystery in biology.

Spirogyra conjugation In many cases, isogamous fertilization is used by organisms that can also reproduce asexually through binary fission, budding, or asexual spore formation. The switch to sexual reproduction mode is often triggered by a change from favorable to unfavorable growing conditions. Fertilization often leads to the formation of a thick-walled zygotic resting spore that can withstand harsh environments and will germinate once growing conditions turn favorable again.

They can appear solitary or clustered. Their texture can likewise be very variable, including fleshy, like charcoal (carbonaceous), leathery, rubbery, gelatinous, slimy, powdery, or cob-web-like. Ascocarps come in multiple colors such as red, orange, yellow, brown, black, or, more rarely, green or blue. Some ascomyceous fungi, such as Saccharomyces cerevisiae, grow as single-celled yeasts, which—during sexual reproduction—develop into an ascus, and do not form fruiting bodies.

This defines a species as It has been argued that this definition is a natural consequence of the effect of sexual reproduction on the dynamics of natural selection. Mayr's use of the adjective "potentially" has been a point of debate; some interpretations exclude unusual or artificial matings that occur only in captivity, or that involve animals capable of mating but that do not normally do so in the wild.

Rufinus's close friend and associate Jerome, who had also studied Origen, however, came to agree with the petition. Around the same time, John Cassian, a Semipelagian monk, introduced Origen's teachings to the West. In 394, Epiphanius wrote to John of Jerusalem, again asking for Origen to be condemned, insisting that Origen's writings denigrated human sexual reproduction and accusing him of having been an Encratite. John once again denied this request.

In their new host, the cercariae become metacercariae by encysting in the tissues. In this inactive state, they wait to be ingested by a mummichog. In its gut, they develop into adult worms ready to undergo sexual reproduction and start the cycle again. Other fish have been identified as also acting as a host to the adult worms, including Menticirrhus saxatilis, Morone americana, Pseudopleuronectes americanus, Tautoga onitis, and Bairdiella chrysura.

Bee pollinating a sunflower. Pollen is transferred from anther of one plant to stigma of another as bee collects nectar Pollen tubes are unique to plants and their structures have evolved over the history of plants. The pollen tube formation is complex and the mechanism is not fully understood, but is of great interest to scientists. Pollen tube formation is important for sexual reproduction to occur in seed plants.

Transformation is a bacterial adaptation involving the transfer of DNA from one bacterium to another through the surrounding liquid medium. Transformation is a bacterial form of sexual reproduction. In order for a bacterium to bind, take up, and recombine exogenous DNA into its chromosome, it must enter a special physiological state referred to as "competence". To determine which molecules may induce competence in L. pneumophila, 64 toxic molecules were tested.

Gooday was born on 19 February 1942 in Colchester the son of William Arnold Gooday and Edith May Beeton. He studied Biology at the University of Bristol graduating BSc in 1963. He took a year out working as a teacher for Voluntary Service Overseas (VSO) in Kenema in Sierra Leone. He receiving a PhD in 1968 from the University of Bristol for research on sexual reproduction in the Mucorales.

Conjugative pili allow for the transfer of DNA between bacteria, in the process of bacterial conjugation. They are sometimes called "sex pili", in analogy to sexual reproduction, because they allow for the exchange of genes via the formation of "mating pairs". Perhaps the most well-studied is the pilus of Escherichia coli, encoded by the fertility F sex factor. A pili is typically 6 to 7 nm in diameter.

Pseudopezicula tetraspora fungi overwinter in leaf litter on the soil surface. If there is sufficient moisture in the spring, fruiting bodies (apothecia) form and produce asci. The asci produce four ascospores each by sexual reproduction. Ascospores are forcibly released from the asci at the end of a rain event following a dry period and are splashed by water or carried by wind to host leaves and flower stems.

This is the first recognized example of an animal species where both females and males can reproduce clonally resulting in a complete separation of male and female gene pools. These ants get the benefits of both asexual and sexual reproduction \- the daughters who can reproduce (the queens) have all of the mother's genes, while the sterile workers whose physical strength and disease resistance are important are produced sexually.

Sexual reproduction derives from recombination, where parent genotypes are reorganized and shared with the offspring. This stands in contrast to single-parent asexual replication, where the offspring is always identical to the parents (barring mutation). Recombination supplies two fault-tolerance mechanisms at the molecular level: recombinational DNA repair (promoted during meiosis because homologous chromosomes pair at that time) and complementation (also known as heterosis, hybrid vigor or masking of mutations).

This flatworm is a generalist carnivore, feeding mostly on earthworms, slugs, snails and small arthropods. It rarely attacks live, uninjured specimens, preferring to feed on dead or injured prey. Sexual reproduction occurs but it is able and frequently does reproduce without mating, producing cocoons containing several hatchlings. The first cocoon is produced 195 (±75) days after hatching and a further cocoon is produced about once a month thereafter.

Rufinus' close friend and associate Jerome, who had also studied Origen, however, came to agree with the petition. Around the same time, John Cassian, a Semipelagian monk, introduced Origen's teachings to the West. In 394, Epiphanius wrote to John of Jerusalem, again asking for Origen to be condemned, insisting that Origen's writings denigrated human sexual reproduction and accusing him of having been an Encratite. John once again denied this request.

Pollination is an important step in the sexual reproduction of higher plants. Pollen is produced by the male flower or by the male organs of hermaphroditic flowers. Pollen does not move on its own and thus requires wind or animal pollinators to disperse the pollen to the stigma (botany) of the same or nearby flowers. However, pollinators are rather selective in determining the flowers they choose to pollinate.

Queen's University Department of Psychology. Signals of fertility in women are often also seen as signals of youth. The evolutionary perspective proposes the idea that when it comes to sexual reproduction, the minimal parental investment required by men gives them the ability and want to simply reproduce 'as much as possible.' It therefore makes sense that men are attracted to the features in women which signal youthfulness, and thus fertility.

The mucus net is a very efficient means of concentrating the minute planktonic particles on which this animal feeds and the appendicularian is in effect, swimming in a concentrated planktonic broth. At 20 °C, Oikopleura cophocerca builds and discards two houses each day. Appendicularians are hermaphrodites and sexual reproduction is the only means of reproduction in this species. The testes ripen first and sperm is shed into the sea.

The polyps of Porites astreoides feed mostly at night, extending their tentacles to catch zooplankton and bacteria. The coral also obtains an important part of its nutritional needs as a result of the photosynthesis performed by the zooxanthellae in sunlight. Some colonies of Porites astreoides are female while others are hermaphroditic. Sexual reproduction occurs with male gametes being released into the sea around the time of the new moon.

That the Japanese' selective breeding with "genetically superior" Chinese women would engender a race of "healthy, sly, cunning coolies", because the Chinese are virtuosi of sexual reproduction. The gist of von Ehrenfels's nihilistic racism was that Asian conquest of the West equalled white racial-annihilation; Continental Europe subjugated by a genetically superior Sino–Japanese army consequent to a race war that the Western world would fail to thwart or win.

D. salina can reproduce asexually through division of motile vegetative cells and sexually through the fusion of two equal gametes into a singular zygote. Though D. salina can survive in salinic environments, Martinez et al. determined that sexual activity of D. salina significantly decreases in higher salt concentrations (>10%) and is induced in lower salt concentrations. Sexual reproduction begins when two D. salina’s flagella touch leading to gamete fusion.

Christian Dumas is a French biologist born on January 2, 1943. He is a professor at the École normale supérieure (ENS) in Lyon. Dumas has devoted himself to the study of the specific sexual reproduction mechanisms of flowering plants and their applications for the genetic improvement of cultivated plants. He is also the scientific director of the botanical garden of the Parc de la Tête d'Or in Lyon.

Sexual reproduction in the well-studied Aiptasia pallida and Aiptasia pulchella, is dioecious, meaning that individual Aiptasia are of separate sexes. During spawning, anemones release their gametes into the water where fertilization occurs. The resulting zygote becomes a free swimming planula larva which eventually settles onto a suitable substrate where it undergoes metamorphosis to become a small polyp. Newly produced larvae are aposymbiotic meaning they do not contain symbionts.

A female (left) and a male (right) mallard (A. platyrhynchos). Like many other species of birds, mallards display striking sexual dimorphism. Most eukaryotes species use sexual reproduction, the division into two sexes is a dimorphism. The question of evolution of sex from asexual reproduction has engaged the attentions of biologists such as Charles Darwin, August Weismann, Ronald Fisher, George C. Williams, John Maynard Smith and W. D. Hamilton, with varied success.

Sexual reproduction occurs after 10 to 12 years of growth; the colony will then reproduce annually for the rest of its life. The male to female polyp ratio is 1:1, with females producing anywhere from 1.2 million to 16.9 million oocytes. A large tall coral tree is somewhere between 30 and 40 years old. The estimated natural lifespan of a black coral colony in the epipelagic zone is 70 years.

The 1.2 billion years old Hunting Formation on Somerset Island, Canada, dates from the end of the Ectasian. It contains the microfossils of the multicellular filaments of Bangiomorpha pubescens (type of red algae), the first taxonomically resolved eukaryote. This was the first organism that exhibited sexual reproduction, which is an essential feature for complex multicellularity. Complex multicellularity is different from "simple" multicellularity, such as colonies of organisms living together.

Jor-El devises a serum to counter this, which he administers to baby Kal-El. DC used this plot device to make Superman Krypton's sole survivor until this was retconned in the mid 2000s to introduce the post-Crisis Kara Zor-El. Krypton was also reimagined as an emotionless and sterile society where all their babies were grown in a birthing matrix as Kryptonians found sexual reproduction to be barbaric.

A. thaliana is a self-pollinating plant compared to other closely related species, meaning it does not require pollen from other plants for fertilization. Self-pollination provides an effective means for plants to colonize new habitats effectively because they do not rely on pollen from another member of their species. By carrying both male and female reproductive organs, the effort for sexual reproduction is greatly diminished but comes at a cost.

Almost all trematodes infect molluscs as the first host in the life cycle, and most have a complex life cycle involving other hosts. Most trematodes are monoecious and alternately reproduce sexually and asexually. The two main exceptions to this are the Aspidogastrea, which have no asexual reproduction, and the schistosomes, which are dioecious. In the definitive host, in which sexual reproduction occurs, eggs are commonly shed along with host feces.

The Y chromosome is one of two sex chromosomes (allosomes) in mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or absence of Y that typically determines the male or female sex of offspring produced in sexual reproduction. In mammals, the Y chromosome contains the gene SRY, which triggers male development.

The uterine transplant is the surgical procedure whereby a healthy uterus is transplanted into an organism of which the uterus is absent or diseased. As part of normal mammalian sexual reproduction, a diseased or absent uterus does not allow normal embryonic implantation, effectively rendering the female infertile. This phenomenon is known as absolute uterine factor infertility (AUFI). Uterine transplant is a potential treatment for this form of infertility.

Two genotypes were found in samples taken from the colony, but they are thought to have arisen through somatic mutation rather than sexual reproduction. Unfortunately, the destruction of about 80% of the colony by fire and construction makes it impossible to definitively settle the question. The caterpillar of the moth Dichomeris juncidella has been reported to feed on the leaves. The berries are eaten by wild turkeys and ruffed grouse.

Most insects are oviparous, where the young hatch after the eggs have been laid. Insect sexual reproduction starts with sperm entry that stimulates oogenesis, meiosis occurs and the egg moves down the genital tract. Accessory glands of the female secrete an adhesive substance to attach eggs to an object and they also supply material that provides the eggs with a protective coating. Oviposition takes place via the female ovipositor.

Tridacna gigas reproduce sexually and are hermaphrodites (producing both eggs and sperm). Self-fertilization is not possible, but this characteristic does allow them to reproduce with any other member of the species. This reduces the burden of finding a compatible mate, while simultaneously doubling the number of offspring produced by the process. As with all other forms of sexual reproduction, hermaphroditism ensures that new gene combinations be passed to further generations.

A far more rudimentary form of double fertilization occurs in the sexual reproduction of an order of gymnosperms commonly known as Gnetales. Specifically, this event has been documented in both Ephedra and Gnetum, a subset of Gnetophytes. In Ephedra nevadensis, a single binucleate sperm cell is deposited into the egg cell. Following the initial fertilization event, the second sperm nucleus is diverted to fertilize an additional egg nucleus found in the egg cytoplasm.

The titan acorn barnacle is a suspension feeder, extending its cirri (modified legs) from the aperture at the top of the shell to catch plankton. As with other barnacles, sexual reproduction involves the passing of sperm along a long slender tube into the mantle cavity of a neighbouring barnacle. Fertilisation is internal and the larvae are planktonic. After passing through several stages over the course of about three weeks, they settle and undergo metamorphosis.

The common intestinal parasite Giardia intestinalis (synonyms Giardia lamblia, G. duodenalis) was once considered to be a descendant of a protist lineage that predated the emergence of meiosis and sex. However, G. intestinalis has now been found to have a core set of genes that function in meiosis and that are widely present among sexual eukaryotes. These results suggested that G. intestinalis is capable of meiosis and thus sexual reproduction. Furthermore, Cooper et al.

PSM V77 D352 The course of the pollen tube in a rock rose One prime example of chemotropism is seen in plant fertilization and pollen tube elongation of angiosperms, flowering plants. Unlike animals, plants cannot move, and therefore needs a delivery mechanism for sexual reproduction. Pollen, which contains the male gametophyte is transferred to another plant via insects or wind. If the pollen is compatible it will germinate and begin to grow.

In female animals, three of the four meiotic products are typically eliminated by extrusion into polar bodies, and only one cell develops to produce an ovum. Because the number of chromosomes is halved during meiosis, gametes can fuse (i.e. fertilization) to form a diploid zygote that contains two copies of each chromosome, one from each parent. Thus, alternating cycles of meiosis and fertilization enable sexual reproduction, with successive generations maintaining the same number of chromosomes.

Lifecycle of Opisthorchis O. viverrini is a hermaphroditic liver fluke. Similar to C. sinensis and O. felineus, it requires three different hosts to complete its lifecycle. Freshwater snails are the first intermediate hosts in which asexual reproduction takes place, and freshwater fishes belonging to the family Cyprinidae) are second intermediate hosts in which larval development occurs. Fish–eating (piscivorous) mammals, including humans, dogs, and cats, act as definitive hosts, in which sexual reproduction occurs.

Saccharomyces paradoxus is naturally homothallic, and is mostly found as diploid in the environment. Reproduction is mostly clonal and 99% of sexual reproduction occurs between spores from the same ascus. This purges recessive deleterious mutations that accumulated during clonal expansion, in a process known as "genome renewal". Post-zygotic isolation between strains of Saccharomyces paradoxus is commonly observed and could be either due to genetic divergence between populations or to chromosomal changes within populations.

Erythronium americanum does not reproduce very effectively via sexual reproduction with only 10% of pollinated flowers developing seeds. The fruit is a 12 to 5 mm long capsule that is held off the ground by the flower stalk. E. americanum is a myrmecochorous plant, meaning that ants help disperse the seeds and reduce seed predation. To make the seeds more appealing to ants they have an elaiosome which is a structure that attracts ants.

In order to sexually reproduce, both males and females need to find a mate. Generally in animals mate choice is made by females while males compete to be chosen. This can lead organisms to extreme efforts in order to reproduce, such as combat and display, or produce extreme features caused by a positive feedback known as a Fisherian runaway. Thus sexual reproduction, as a form of natural selection, has an effect on evolution.

The bryophytes, which include liverworts, hornworts and mosses, reproduce both sexually and vegetatively. They are small plants found growing in moist locations and like ferns, have motile sperm with flagella and need water to facilitate sexual reproduction. These plants start as a haploid spore that grows into the dominant gametophyte form, which is a multicellular haploid body with leaf-like structures that photosynthesize. Haploid gametes are produced in antheridia (male) and archegonia (female) by mitosis.

Schizocyathus fissilis is an azooxanthellate coral which does not harbour symbiotic zooxanthellae in its tissues. It feeds by extending its tentacles to catch plankton and by absorbing organic matter from the water. Sexual reproduction takes place with the liberation of sperm and eggs into the water column. The planula larvae drift with the currents, and when fully developed, settle on the seabed and undergo metamorphosis into polyps which secrete their own calcium carbonate skeletons.

A clear distinction from Naegleria is the absence of the interzonal bodies during nuclear division. As of yet, no sexual reproduction has been observed, but asexual reproduction has been described in both the flagellated and the amoeboid stages. The temporary flagellated stage is often between 16.5 and 25 μm in size with a mean cell volume of 2500 μm3. It usually features 4 flagella and lacks a cytosome, however their size and structure can vary.

When Muller introduced the phenomenon of clonal interference, he used it to explain why sexual reproduction evolved. He reasoned that the loss of beneficial mutations because of clonal interference inhibits the adaptivity of asexually reproducing species. Sex and other reproductive strategies involving recombination would therefore be evolutionary advantageous according to Muller. From the 1970’s however, biologists have demonstrated that asexually and sexually reproducing strategies yield the same rate of the evolutionary adaptivity.

Both asexual and sexual reproduction can be found in sipunculans, although asexual reproduction is uncommon and has only been observed in Aspidosiphon elegans and Sipunculus robustus. These reproduce asexually through transverse fission, followed by regeneration of vital body components, with S. robustus also reproducing by budding. One species of sipunculan, Themiste lageniformis, has been recorded as reproducing parthenogenetically; eggs produced in the absence of sperm developed through the normal stages. Most sipunculan species are dioecious.

Not all trematodes follow the typical sequence of eggs, miracidia, sporocysts, rediae, cercariae, and adults. In some species, the redial stage is omitted, and sporocysts produce cercariae. In other species, the cercaria develops into an adult within the same host. Many digenean trematodes require two hosts; one (typically a snail) where asexual reproduction occurs in sporocysts, the other a vertebrate (typically a fish) where the adult form engages in sexual reproduction to produce eggs.

Although sexual reproduction is by far the most common in Eunectes, E. murinus has been observed to undergo facultative parthenogenesis. In both cases, the females had lived in isolation from other anacondas for over eight years, and DNA analysis showed that the few fully formed offspring were genetically identical to the mothers; although this is not commonly observed, it is likely possible in all species of Eunectes and several other species of Boidae.

Lactuca serriola is the wild progenitor of cultivated lettuce (Lactuca sativa), and can be affected by lettuce downy mildew, one of the most serious diseases of lettuce. L. serriola has shown resistance to the plant pathogen Bremia lactucae, the cause of the disease. This pathogen is able to undergo sexual reproduction, and once virulent strains have been produced, can undergo rapid asexual reproductive cycles. As a result, there are many strains, which vary in virulence.

Most species use sexual reproduction, releasing sperm cells into the water to fertilize ova that in some species are released and in others are retained by the "mother." The fertilized eggs develop into larvae, which swim off in search of places to settle. Sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. A few species reproduce by budding.

Sexuality in the Philippines encompasses sexual behavior, sexual practices, and sexual activities exhibited by men and women of the Philippines past and the present. It covers courtship strategies for attracting partners for physical and emotional intimacy, sexual contact, sexual reproduction, building a family, and other forms of individual interactions or interpersonal relationships, as set and dictated by their culture and tradition, religion, beliefs, values and moral convictions, psychology, foreign influences, and other related factors.

Like almost all members of the Naidinae, Chaeogaster species normally reproduce asexually. They thereby form characteristic chains of two or three worms that come into being through a form of budding. These chains give rise to new individuals through division (paratomy), which have, because of the asexual nature of the multiplication, the same genetic blueprint as the original worm. However, the worms switch to sexual reproduction during difficult times like the winter.

Feeding and sexual reproduction both take place upon algal beds which provide a source of food and protection for A. punctata. Their coloration is usually determined from the pigments in the seaweed they feed upon which in turn also provides them with camouflage. Mediterranean species of A. punctata feed primarily on red algae of the genus Laurencia which provide them with metabolites known to produce antifungals, antivirals, and cytotoxins for self defense.

Asexual reproduction occurs via vegetative spores (conidia) or through mycelial fragmentation. Mycelial fragmentation occurs when a fungal mycelium separates into pieces, and each component grows into a separate mycelium. Mycelial fragmentation and vegetative spores maintain clonal populations adapted to a specific niche, and allow more rapid dispersal than sexual reproduction. The "Fungi imperfecti" (fungi lacking the perfect or sexual stage) or Deuteromycota comprise all the species that lack an observable sexual cycle.

Cellular differentiation is an essential function of the archaeocyte. All specialized cells within the sponge have its origins with the archaeocyte. This is especially important in reproduction as the sex cells of the sponge in sexual reproduction are formed from these amoeboid cells. Similarly in asexual reproduction amoebocytes result in the formation of gemmules which are cyst- like spheres containing more amoebocytes as well as other sponge cells including the phylum specific choanocyte.

Ceratocystis paradoxa or Black Rot of Pineapple is a plant pathogen that is a fungus part of the phylum Ascomycota. It is characterized as the teleomorph or sexual reproduction stage of infection. This stage contains ascocarps, or sacs/fruiting bodies, which contain the sexually produced inoculating ascospores. These are the structures which are used primarily to survive long periods of time or overwinter to prepare for the next growing season of its host.

Blue-tailed damselflies (Ischnura elegans) mating In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms, usually for the purposes of sexual reproduction. Some definitions limit the term to pairing between animals, while other definitions extend the term to mating in plants and fungi. Fertilization is the fusion of two gametes. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization.

Soybean aphid alternates between hosts and between asexual and sexual reproduction. The simplest reproductive strategy is for an aphid to have a single host all year round. On this it may alternate between sexual and asexual generations (holocyclic) or alternatively, all young may be produced by parthenogenesis, eggs never being laid (anholocyclic). Some species can have both holocyclic and anholocyclic populations under different circumstances but no known aphid species reproduce solely by sexual means.

Maturing rapidly, females breed profusely so that the number of these insects multiplies quickly. Winged females may develop later in the season, allowing the insects to colonise new plants. In temperate regions, a phase of sexual reproduction occurs in the autumn, with the insects often overwintering as eggs. The life cycle of some species involves an alternation between two species of host plants, for example between an annual crop and a woody plant.

Pierre Augustin Dangeard Pierre Clement Augustin Dangeard (23 November 1862, Ségrie – 10 November 1947, Ségrie) was a botanist and mycologist known for his investigations of sexual reproduction in fungi. He was the father of botanist Pierre Dangeard (1895–1970) and geologist Louis Dangeard (1898–1987). Beginning in 1883, he worked as a préparateur to the faculty at Caen, earning his doctorate in 1886. Following graduation, he served as chief of travaux de botanique.

Allogromia laticollaris is perhaps the best- studied foraminiferan amoeboid for autogamy. Allogromia laticollaris can alternate between sexual reproduction via cross-fertilization and asexual reproduction via binary fission. The details of the life cycle of Allogromia laticollaris are unknown, but similar to Paramecium aurelia, Allogromia laticollaris is also shown to sometimes defer to autogamous behavior when placed in nutritional stress. As seen in Paramecium, there is some nuclear dimorphism observed in Allogromia laticollaris.

The female gametophyte produces an egg in the oogonium, and the male gametophyte releases motile sperm that fertilize the egg. The fertilized zygote then grows into the mature diploid sporophyte. In the order Fucales, sexual reproduction is oogamous, and the mature diploid is the only form for each generation. Gametes are formed in specialized conceptacles that occur scattered on both surfaces of the receptacle, the outer portion of the blades of the parent plant.

Aphid populations are often entirely female during the summer, with sexual reproduction only to produce eggs for overwintering. Some species can alternate between sexual and asexual strategies, an ability known as heterogamy, depending on many conditions. Alternation is observed in several rotifer species (cyclical parthenogenesis e.g. in Brachionus species) and a few types of insects, such as aphids which will, under certain conditions, produce eggs that have not gone through meiosis, thus cloning themselves.

The gemmules were dispersed around the organism and could multiply by division. In sexual reproduction they were transmitted from parents to their offspring with the mixing of the gemmules producing offspring with 'blended' characteristics of the parents. Gemmules could also remain dormant for several generations before becoming active. He also suggested that the environment might affect the gemmules in an organism and thus allowed for the possibility of the Lamarckian inheritance of acquired characteristics.

Although euglenids share several common characteristics with animals, which is why they were originally classified as so, no evidence has been found of euglenids ever using sexual reproduction. This is one of the reasons they could no longer be classified as animals. For euglenids to reproduce, asexual reproduction takes place in the form of binary fission, and the cells replicate and divide during mitosis and cytokinesis. This process occurs in a very distinct order.

The pathogen grows voraciously in areas with high humidity and heavy rainfall in addition to an optimal pH of 6.5 and temperature of . The aforementioned cool, wet, and humid conditions favor both the asexual and sexual reproduction of Phytophthora colocasiae. The ideal temperature range for this pathogen is . Sporangia, which develop most rapidly at margins of leaf lesions, can germinate directly on leaves at temperatures ranging from , or spread to neighboring leaves via rain splash.

The plant retains them all winter. They are dry and not tasty, though the Indians of Arizona and New Mexico are said to have eaten them. In addition to sexual reproduction, the tree cholla reproduces when stem joints fall to the ground and take root. Thus this species spreads and its spread is hard to control, especially where animals defecate seeds and carry stem joints stuck to their hide some distance from the parent plant.

Bernard Ogilvie Dodge (18April 18729August 1960) was an American botanist and pioneer researcher on heredity in fungi. Dodge was the author of over 150 papers dealing with the life histories, cytology, morphology, pathology and genetics of fungi, and with insects and other animal pests of plants. He made the first studies of sexual reproduction in the common bread mold, Neurospora.Lindegren, Carl C. Reminiscences of B.O. Dodge and the Beginnings of Neurospora Genetics.

Abstract Aristotle noted that the octopus had a hectocotyl arm and suggested it might be used in sexual reproduction. This claim was widely disbelieved until the 19th century. It was described in 1829 by the French zoologist Georges Cuvier, who supposed it to be a parasitic worm, naming it as a new species, Hectocotylus octopodis. Other zoologists thought it a spermatophore; the German zoologist Heinrich Müller believed it was "designed" to detach during copulation.

Sexual reproduction in flowering plants involves the union of the male and female germ cells, sperm and egg cells respectively. Pollen is produced in stamens, and is carried to the pistil, which has the ovary at its base where fertilization can take place. Within each pollen grain is a male gametophyte which consists of only three cells. In most flowering plants the female gametophyte within the ovule consists of only seven cells.

They probably spread by a combination of vegetative reproduction forming clonal colonies, and sexual reproduction via spores and did not grow much more than a few centimeters tall. By the Late Devonian, forests of large, primitive plants existed: lycophytes, sphenophytes, ferns, and progymnosperms had evolved. Most of these plants have true roots and leaves, and many were quite tall. The tree-like Archaeopteris, ancestral to the gymnosperms, and the giant cladoxylopsid trees had true wood.

Anisogamy (also called heterogamy) is the form of sexual reproduction that involves the union or fusion of two gametes, which differ in size and/or form. (The related adjectives are anisogamous and anisogamic.) The smaller gamete is considered to be male (a sperm cell), whereas the larger gamete is regarded as female (typically an egg cell, if non-motile). There are several types of anisogamy. Both gametes may be flagellated and therefore motile.

Modern commercially farmed banana plants are reproduced asexually, by replanting the plant's basal shoot that grows after the original plant has been cut down. Being triploid, the fruit contains no seeds, and the male flower does not produce pollen suitable for pollination, prohibiting sexual reproduction. This causes all bananas of a single breed to be nearly genetically identical. The fungus easily spreads from plant to plant because the individual plants' defenses are nearly identical.

These larvae colonize and feed on the roots of nearby Chenopodiaceae plants for the rest of the summer. In the summer, they form alate migrants that fly back to the Populus tree and asexually produce sexual males and females whose sole purpose is to mate, as they lack mouthparts to feed. The product of sexual reproduction is a single egg in each female which is deposited in the tree's bark and left to overwinter.

The reproduction of the genus Drymonema is similar to the reproduction of all Scyphozoans. These organisms can undergo both sexual (medusa) and asexual (polyp) reproduction processes. In the case of a medusa, sexual reproduction is external, where the males release the sperm while the females release eggs into the water and they fuse. This fusion results in free swimming planula larva that eventually sinks to the bottom or finds a hard surface to attach to.

In heterothallic species, sexual reproduction occurs when opposite mating types (designated + and -) come into close proximity, inducing the formation of specialized hyphae called gametangia. The gametangia grow toward each other, then fuse, forming a diploid zygote at the point of fusion. The zygote develops a resistant cell wall, forming a single-celled zygospore, the characteristic that gives its name to this group of fungi. Meiosis occurs within the zygospore (see article Phycomyces).

Homologous chromosomes are separated in the first division, and sister chromatids are separated in the second division. Both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. Both are believed to be present in the last eukaryotic common ancestor. Prokaryotes (bacteria and archaea) usually undergo a vegetative cell division known as binary fission, where their genetic material is segregated equally into two daughter cells.

One meadow of cloned eelgrass was determined to be 3000 years old, genetically. When undergoing sexual reproduction, the plant produces large quantities of seeds, at times numbering several thousand seeds per square meter of plants. The plant disperses large distances when its stems break away and carry the fertile seeds to new areas, eventually dropping to the seabed. The seagrass is a favorite food of several species of waterfowl, which may also distribute the seeds.

Courtship ritual and mating Sexual reproduction involves courtship rituals. During the mating season between April and November, females lay their eggs in the open; about 1–25 eggs incubate underground for 100 days. The sex of the eggs is determined by the temperature where they are incubated in a nest laid below sand. If the sand is over 30 degrees Celsius, it's a female and if below 30 degrees Celsius, the egg is a male.

This coral contains the chemical unpalatable chimyl alcohol for defensive purposes. This is insufficient to prevent the nudibranch Tritoniella belli from feeding on it, and the nudibranch incorporates the substance into its own tissues, making it distasteful to predatory starfish such as Odontaster validus, Perknaster fuscus and Acodontaster conspicuus. Reproduction in this coral can occur at any time of year and is by fission or by sexual reproduction, with the release of larvae.

The F1 generation of the asexual dandelions will contain the same ratio as the P-generation. Conversely, following standard principles of sexual reproduction, the F1 generation will be 25% A1A1, 25% A2A2, and 50% A1A2. With the addition of differential survival related to these genotypes (certain genotypes surviving better in different degrees of sunlight), the asexual population will eventually drift toward one genotype and die off when the environment changes to suit a different genotype.

In a rather different forms of sexual reproduction, it has been found that on some occasions, the eggs and developing larvae are brooded in the maternal polyps. Some individual colonies have even been seen adopting both breeding strategies at the same time in different parts of the colony. C. aspera is a zooxanthelate coral. In its tissues it contains symbiotic unicellular photosynthetic organisms that provide nutrients and energy for the coral host.

Saccinobaculus is observed to have both sexual and asexual life cycles. Sexual reproduction only occurs around the time when the insect-host is molting and is triggered by hormones from the insect's prothoracic glands. About a week before the insect host molts, Saccinobaculus produces gametes from a haploid cell through a single mitotic division of the nucleus and cytoplasm. Immediately after the gametes are formed, they unite to begin the process of fertilization.

Grafting, 1870, by Winslow Homer an example of grafting. Fruit tree propagation is usually carried out vegetatively (non-sexually) by grafting or budding a desired variety onto a suitable rootstock. Perennial plants can be propagated either by sexual or vegetative means. Sexual reproduction begins when a male germ cell (pollen) from one flower fertilises a female germ cell (ovule, incipient seed) of the same species, initiating the development of a fruit containing seeds.

A macrocyst is an aggregate of cells of Dictyostelids formed during sexual reproduction enclosed in a cellulose wall. If two amoebae of different mating types are present in a dark and wet environment, they can fuse during aggregation to form a giant cell. The giant cell will then engulf the other cells in the aggregate and encase the whole aggregate in a thick, cellulose wall to protect it. This is known as a macrocyst.

The life cycle of this seaweed includes sexual reproduction and spore-producing asexual reproduction. In Britain the fronds die back in winter and the rhizoids resprout in the early summer, producing new fronds. After about twenty days these are mature, long or more, and produce tetraspores in concentric rings a millimetre or so wide. By the time the frond reaches a length of it will have produced six to twelve generations of tetraspores.

As layering is not a process involving sexual reproduction the new plants are clones of the parent tree and all of the new individuals formed have identical DNA with each other and the parent. Estimates for the tree's age are for 600 to 700 years. The clonal grove has achieved a second row of branch layering and the crown has reached a circumference of 328ft or 100m. The parent tree has a girth of 27ft or 8.86m at 30cm.

Chaetomium cupreum is known only as a sexually reproducing species and no asexual form has been reported. Ames originally reported C. cupreum to possess a homothallic mating system but this was later contradicted by Tveit in 1955 who determined the species to be heterothallic. Sexual reproduction in C. cupreum involves the formation of ascogonia arising as lateral outgrowths of the vegetative mycelium. In early developmental stages, the ascogonia are coiled and coenocytic with septa forming as the ascogonia mature.

Nonetheless, circumstantial chemical evidence has been found for the existence of angiosperms as early as 250 million years ago (see the above Paleozoic section) In 2013 flowers encased in amber were found and dated 100 million years before present. The amber had frozen the act of sexual reproduction in the process of taking place. Microscopic images showed tubes growing out of pollen and penetrating the flower's stigma. The pollen was sticky, suggesting it was carried by insects.

Gender is a significant phenomenon in Chinese mythology. On the one hand, there are traditions about sexual reproduction, fertility/mother goddesses, and evidence by scholars (such as Jordan Paper) of a patriarchal influence over time. Tu'er Shen is an example of a gender-oriented deity. The marking of gender in Chinese is different than in English, especially in Classical Chinese, gender is not marked in the case of most nouns and pronouns, thus making gender often difficult to determine.

In April and May 2012 Representative Wyatt expressed deep opposition to Missouri House Bill 2051, commonly known as the "Don't Say Gay" bill. The bill would put strict limits on the discussion of sexual orientation in Missouri schools, limiting it only to classes on health and sexual reproduction. The bill gained nationwide attention from various news outlets and The Colbert Report. On May 2, 2012 Wyatt held a press conference at the Missouri State Capitol outlining his opposition.

Humans are now considered as the accidental host because humans are not the primary requirement for the life cycle; pigs are recognised as the principal definitive host. Infection causes a helminthic disease called gastrodiscoidiasis. It is a digenetic trematode with a complex life cycle involving asexual reproduction in an intermediate host, presumably aquatic snails, and sexual reproduction in the vertebrate host. As a hermaphrodite, eggs are produced by self-fertilisation and are released along the faeces of the host.

Potamopyrgus antipodarum tends to reproduce sexually when in the presence of trematode parasites. The New Zealand freshwater snail Potamopyrgus antipodarum and its different trematode parasites represent a rather special model system. Populations of P. antipodarum consist of asexual clones and sexual individuals and therefore can be used to study the evolution and advantages of sexual reproduction. There is a high correlation between the presence of parasites and the frequency of sexual individuals within the different populations.

Hydrozoans have two distinct stages in their life, a polyp stage and a medusa stage. The polyp stage is benthic, with the cells forming colonies, while the medusa stage is a singular, planktonic organism. Generally in hydrozoa the medusa develops from the asexual budding of the polyp and the polyp results from sexual reproduction of medusae. In T. nutricula, planktonic medusa have the capability to bud polyps or medusae which also have the ability to spawn new medusae.

The narrator His name is not mentioned in the novel. Unlike that of his inseparable dog, which is called ‘Anders’ (translates to: ‘different’ from Dutch). is a biologist who became a local celebrity in his village, Monward, thanks to his book “The Reckless Outsider”, which describes the differences between sexual reproduction and cloning. While posing naked for a painter named Molly, he meets Lotte, a photographer who is working on a photo book of racy people in Monward.

Olfaction is a very important aspect in sexual reproduction throughout evolution because it triggers mating behaviour in many species. Pheromones as olfactory chemical signals allow for members of the same species to perceive when other members are ready for reproduction. It can also lead to the synchronization of menstrual cycles in females within the species and influence sexual attraction between members within the species. Having an unconscious memory for such processes has allowed for species to survive.

In animal cells, chromosomes reach their highest compaction level in anaphase during chromosome segregation. Chromosomal recombination during meiosis and subsequent sexual reproduction play a significant role in genetic diversity. If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe. Usually, this will make the cell initiate apoptosis leading to its own death, but sometimes mutations in the cell hamper this process and thus cause progression of cancer.

For the later, females need to produce sons asexually. The same or other females can switch at any moment from asexual to sexual reproduction, but producing haploid eggs, which require fertilization by males. The sexual eggs are then deposited in an ephippium (plural: ephippia, a resting egg shell), which will sink into the bottom of the water body when the female molts her carapace. After a resting period, which can last several years, the resting stages hatches.

He received Linnaeus into his home and allowed him use of his library, which was one of the richest botanical libraries in Sweden.Stöver (1794), pp. 19–20. In 1729, Linnaeus wrote a thesis, ' on plant sexual reproduction. This attracted the attention of Rudbeck; in May 1730, he selected Linnaeus to give lectures at the University although the young man was only a second-year student. His lectures were popular, and Linnaeus often addressed an audience of 300 people.

Green plants obtain most of their energy from sunlight via photosynthesis by primary chloroplasts that are derived from endosymbiosis with cyanobacteria. Their chloroplasts contain chlorophylls a and b, which gives them their green color. Some plants are parasitic or mycotrophic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize, but still have flowers, fruits, and seeds. Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is also common.

Conidia are dull grey green or grey turquoise in colour. No known sexual reproduction has been described. Penicillium commune can be distinguished by its fast growth on creatine sucrose neutral agar (CSN) while showing a slow growth rate on malt extract agar (MEA) and restricted growth on Czapek medium (CZA) and Czapek yeast extract agar (CYA). The appearance of colonies on MEA ranges from soft, velvety and grown in unison to granular and barely grown together.

In mammals it occurs in the seminiferous tubules of the male testes in a stepwise fashion. Spermatogenesis is highly dependent upon optimal conditions for the process to occur correctly, and is essential for sexual reproduction. DNA methylation and histone modification have been implicated in the regulation of this process. It starts at puberty and usually continues uninterrupted until death, although a slight decrease can be discerned in the quantity of produced sperm with increase in age (see Male infertility).

Studies of Entamoeba invadens found that, during the conversion from the tetraploid uninucleate trophozoite to the tetranucleate cyst, homologous recombination is enhanced. Expression of genes with functions related to the major steps of meiotic recombination also increase during encystations. These findings in E. invadens, combined with evidence from studies of E. histolytica indicate the presence of meiosis in the Entamoeba. Dictyostelium discoideum in the supergroup Amoebozoa can undergo mating and sexual reproduction including meiosis when food is scarce.

Cell-cell fusogens have several different applications. These chemical agents can play a significant part in sexual and asexual reproduction by promoting the fusion of the membrane bilayers. With sexual reproduction, evidence found to prove that in mice, some mandatory sperm-egg fusogens are responsible for fusion; two particular proteins were IZUMO1 and CD9. After comparing the data of experiments done with plants, fungi, and invertebrates, it was seen that several crucial genes could have been responsible for fertilization.

In certain species of diatoms, auxospores are specialised cells that are produced at key stages in their cell cycle or life history. Auxospores typically play a role in growth processes, sexual reproduction or dormancy.Hoek, C. van den, Mann, D. G. and Jahns, H. M. (1995). Algae : An introduction to phycology, Cambridge University Press, UK. Auxospores are involved in re-establishing the normal size in diatoms because successive mitotic cell divisions leads to a decrease in cell size.

Thus, karyogamy is the key step in bringing together two sets of different genetic material which can recombine during meiosis. In haploid organisms that lack sexual cycles, karyogamy can also be an important source of genetic variation during the process of forming somatic diploid cells. Formation of somatic diploids circumvents the process of gamete formation during the sexual reproduction cycle and instead creates variation within the somatic cells of an already developed organism, such as a fungus.

In the heterothallic species Neurospora crassa, interaction of haploid strains of opposite mating type is necessary for the occurrence of sexual reproduction and the production of ascospores by meiosis. Ascospores then restore haploid individuals of either mating type. The life cycle phase is thus predominantly haploid, however, upon mating, the nuclei do not immediately fuse: karyogamy is delayed until the very onset of meiosis. The resulting mycelium is called a heterokaryon, and is neither diploid, nor haploid.

The fragments are motile and regenerate the head plate and pharynx in a few weeks. Such a reproduction strategy is considered one of the reason for the successful colonization of this and other species of Bipalium. Although there is little evidence of sexual reproduction in these planarians, there have been several reported cases of egg capsules being discovered. The egg capsules discovered had several of the same characteristics of those of B. adventitium, including coloration and incubation period.

Symbiosis, Philadelphia, Pa.(USA) However, in recent years, through molecular methods, evidence of recombination and sexual fusions of gamates of the same size suggests the occurrence of sexual reproduction. The zygotes, quite distinct from zoospores, are 6.6 um in diameter and smooth walled with two round chloroplasts. First, the gametes pair up and fuse with each other, leading to the formation of zygotes. Then, the flagella disappear and the zygote develops in a normal vegetative pattern.

Inside the macrocyst, the giant cell divides first through meiosis, then through mitosis to produce many haploid amoebae that will be released to feed as normal amoebae would. Homothallic D. discoideum strains AC4 and ZA3A are also able to produce macrocysts. Each of these strains, unlike heterothallic strains, likely express both mating type alleles (matA and mata). While sexual reproduction is possible, it is very rare to see successful germination of a D. discoideum macrocyst under laboratory conditions.

Ascus of Hypocrea virens with eight two- celled Ascospores Sexual reproduction in the Ascomycota leads to the formation of the ascus, the structure that defines this fungal group and distinguishes it from other fungal phyla. The ascus is a tube-shaped vessel, a meiosporangium, which contains the sexual spores produced by meiosis and which are called ascospores. Apart from a few exceptions, such as Candida albicans, most ascomycetes are haploid, i.e., they contain one set of chromosomes per nucleus.

More genetic variation was found with respect to diploid (2n) to triploid (3n) ratio occurred among individuals than within individuals. Also, diploid cells exclusively participated in meiosis and subsequent sexual reproduction for males, so balanced gametes and normal fertility occurred. This is a rare event because of the limited viable polyploid individuals that occur in natural vertebrate populations. The lizard genus Lacerta and fish genus Phoxinus are the only other known examples of diploid-triploid mosaicism.

They are white at first but become yellow to pale brown and very dark brown as they mature. The hyphae of B. trispora are aseptate, very dense, and highly branched. Sexual reproduction is by the formation of zygospores, which contain high concentrations of triglycerol-rich lipids and phosphatidylcholine. Zygospores can persist for long periods of time, and their germination is dependent on a cytoplasmic regulatory system that sustains dormancy and forestalls germination in the presence of unfavorable growth conditions.

Critics and analysts have focused on interpretations of the film's representation of sexuality and gender identity. Sharalyn Orbaugh has noted that the opening scene of Ghost in the Shell begins with the "perfect paradoxical introduction to a narrative that is all about the nature of sex/gender identity and self-identity in general in a future world where sexual reproduction has given way to mechanical replication".Orbaugh, Sharalyn. "The Genealogy of the cyborg in Japanese popular culture".

A. lentulus is an opportunistic human pathogen that causes invasive aspergillosis with high mortality rates. In 2013, A. lentulus was found to have a heterothallic functional sexual breeding system. A. terreus is commonly used in industry to produce important organic acids and enzymes, and was the initial source for the cholesterol-lowering drug lovastatin. In 2013, A. terreus was found to be capable of sexual reproduction when strains of opposite mating types were crossed under appropriate culture conditions.

Aristotle reports on the sea- life visible from observation on Lesbos and the catches of fishermen. He describes the catfish, electric ray, and frogfish in detail, as well as cephalopods such as the octopus and paper nautilus. His description of the hectocotyl arm of cephalopods, used in sexual reproduction, was widely disbelieved until the 19th century. He gives accurate descriptions of the four-chambered fore-stomachs of ruminants, and of the ovoviviparous embryological development of the hound shark.

Turtle grass can reproduce both through vegetative and sexual reproduction. The main propagation method is by extension of the underground rhizome, or stem. This increase in rhizome length results in asexual ramets, or clonal colonies which are genetic replicates of the parent plant. Although asexual propagation results in an increase in the size of the turtle grass bed, extensive asexual reproduction limits genetic diversity and can put the meadow at severe risk if there is a disease outbreak.

Alternaria dauci lesion Sexual reproduction of Alternaria dauci is not known to occur, and the disease is most active during spring, summer, and autumn cropping cycles. The disease cycle begins when fungus overwinters on or in host seed and in soil-borne debris from carrot. A. dauci may also be spread into fields via contaminated carrot seeds during cultivation. Once introduced, the pathogen can persist in carrot debris or contaminated seeds in the soil for up to two years.

Although Paracatenula produce sperm and eggs that can be very informative to differentiate between species, sexual reproduction has not been observed. Instead, the worms reproduce by asexual fission or fragmentation, a process called paratomy. Paracatenula worms have high regenerative capabilities and can regenerate a lost head including the brain within 10-14 days The bacteriocytes of dividing worms are split during the fission process and the population of symbiotic bacteria is distributed to the two daughter individuals.

Holothuria hilla is a detritivore, raking sand into its mouth with its oral tentacles, extracting and digesting the bacteria, animal and vegetal particles, and voiding the sand through its anus. In this way it churns up significant areas of the seabed. Reproduction is either sexual, when the male and female liberate their gametes into the water column, or asexual, by fission. Sexual reproduction mostly occurs at hotter times of year and asexual reproduction when it is cooler.

Individuals in social colonies and modular organisms receive benefit to such a lifestyle. For example, it may be easier to seek out food, defend a nesting site, or increase competitive ability against other species. Modular organisms' ability to reproduce asexually in addition to sexually allows them unique benefits that social colonies do not have. The energy required for sexual reproduction varies based on the frequency and length of reproductive activity, number and size of offspring, and parental care.

Protists have the advantage of diversifying their modes of reproduction. This is useful for a multitude of reasons. First, if there is an unfavorable change in the environment that puts the ability to deliver offspring at risk, then it is advantageous for an organism to have autogamy at its disposal. In other organisms, it is seen that genetic diversity arising from sexual reproduction is maintained by changes in the environment that favor certain genotypes over others.

Microalgae are microscopic organisms that can grow via photosynthesis. Many groups grow quickly and are more productive than land plants and macroalgae (seaweed). Microalgae reproduction occurs primarily by vegetative (asexual) cell division, although sexual reproduction can occur in many species under appropriate growth conditions. Microalgae are efficient for fuel production and they are capable of taking a waste (zero-energy) form of carbon () and converting it into a high density liquid form of energy (natural oil).

If, as evidence indicates, sexual reproduction arose very early in eukaryotic evolution, the essential features of meiosis may have already been present in the prokaryotic ancestors of eukaryotes. In extant organisms, proteins with central functions in meiosis are similar to key proteins in natural transformation in bacteria and DNA transfer in archaea.Bernstein, H., Bernstein, C. Evolutionary origin and adaptive function of meiosis. In "Meiosis", Intech Publ (Carol Bernstein and Harris Bernstein editors), Chapter 3: 41-75 (2013).

This idea is sometimes referred to as the two-fold cost of sexual reproduction. It was first described mathematically by John Maynard Smith. In his manuscript, Smith further speculated on the impact of an asexual mutant arising in a sexual population, which suppresses meiosis and allows eggs to develop into offspring genetically identical to the mother by mitotic division. The mutant-asexual lineage would double its representation in the population each generation, all else being equal.

It has been mistaken in the past as A. melanoxylon, A. myrtifoliia, and A. mucronata and has been suggested to be a hybrid due to its rarity and limited sexual reproduction, however has multiple morphological differences. Most closely related to A. kettlewelliae, which is distinguished especially by its more elongate phyllodes with the gland 5–15 mm above the pulvinus and pods 5–10 cm long and is a species that occurs only on the mainland of Australia.

An animal chimera is a single organism that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction. If the different cells have emerged from the same zygote, the organism is called a mosaic. Chimeras are formed from at least four parent cells (two fertilised eggs or early embryos fused together). Each population of cells keeps its own character and the resulting organism is a mixture of tissues.

The (-) strain loses sexual capacity faster than the (+) strain. As Mucor mucedo are heterothallic, the hyphae taking part in the sexual reproduction have to be of two different strains, either (+) or (-). When these make contact an extension of the hyphae called progametangia are formed and most of the nuclei and cytoplasm accumulate at the ends. Septa form adjacent to the point of contact, and the terminal component, gametangia, are visible with elongated cells called suspensors attached to it.

In particular, these species have seven genes that encode proteins whose only known function is in meiosis, including Dmc1 that is a meiosis-specific recombinase. Since meiosis is considered to be a hallmark of sexual reproduction, it might be expected that a sexual stage or a sexual apparatus should be present. However, as yet, none has been identified. In addition, mating type gene homologues and a putative sex hormone-sensing pathway were detected in these fungi.

The Membrane Occupation and Recognition Nexus is a repeat is found in multiple copies in several proteins including junctophilins. A MORN-repeat protein has been identified in the parasite Toxoplasma gondii and other Apicomplexan protists. In T. gondii, MORN1 plays role in nuclear division and daughter cell budding. It is specifically associated with the spindle poles, the anterior and interior rings of the inner membrane complex during asexual reproduction/sexual reproduction; budding; and schizogony (see Apicomplexan cellular morphology).

These two aspects have been proposed to have two natural selective advantages, respectively. Meiosis is proposed to be adaptive because it facilitates recombinational repair of DNA damages that are otherwise difficult to repair. Outcrossing is proposed to be adaptive because it facilitates complementation, that is the masking of deleterious recessive alleles (also see Heterosis). The benefit of masking deleterious alleles has been proposed to be a major factor in the maintenance of sexual reproduction among eukaryotes.

Leishmania braziliensis, like other species of Leishmania rely on asexual reproduction in the intermediate mammalian host to greatly increase population density. Such reproduction is often witnessed in mononuclear phagocytes (dendritic cells, monocytes, neutrophils) of the mammalian host, with the macrophages being the target white blood cell of the parasite. Recently, it has been hypothesized through two studies that certain members of Leishmania genus (e.g. L. braziliensis) are capable of sexual reproduction in the gut of the sand-fly vector.

More work is needed to establish a clear pattern of sexual reproduction in the genus. The reproduction of Leishmania braziliensis vector, the sandfly, is dependent on environmental conditions. Environmental conditions such as high humidity, higher temperatures, deforestation add an increased risk because it causes increased reproduction of the parasite carrying sandflies. These environmental changes put more people at risk with the vector and cause a greater geographic distribution of the sandfly and, consequently, the infectious disease.

Sexual reproduction involves the liberation of sperm and eggs into the sea and the development and eventual settlement of planktonic larvae. Asexual reproduction is by fragmentation, each portion being the same sex as its parent. Small, immature individuals (disc diameter under ) usually have six arms and can split themselves in two and then regenerate the missing parts of the disc and arms, often ending up with five arms. Most larger individuals have five arms and can also undergo fragmentation.

Sexual reproduction occurs in two fundamentally different ways. This is by outcrossing (heterothallic sex), in which two distinct individuals contribute nuclei, or by homothallic sex or self-fertilization (selfing) in which both nuclei are derived from the same individual. Selfing in A. nidulans involves activation of the same mating pathways characteristic of sex in outcrossing species, i.e. self-fertilization does not bypass required pathways for outcrossing sex but instead requires activation of these pathways within a single individual.

In sexual reproduction, males may release sperm to stimulate females to release eggs, and fertilization occurs, either internally in the gastrovascular cavity or in the water column. The eggs and sperm, or the larvae, are ejected through the mouth. In many species the eggs and sperm rise to the surface where fertilisation occurs. The fertilized egg develops into a planula larva, which drifts for a while before sinking to the seabed and undergoing metamorphosis into a juvenile sea anemone.

This is referred to as the "parasitic" tactic, where the smaller male effectively cheats its way to accessing females, by reaping the benefit of sexual reproduction without contributing resources that normally attract females. Models such as this provide valuable tools for research aimed at energetic constraints and environmental cues involved in cheating. Studies find that mating strategies are highly adaptable and depend on a variety of factors, such as competitiveness, energetic costs involved in defending territory or acquiring resources.

Halteria cells can reproduce sexually through a process that has been studied specifically in H. grandinella. During sexual reproduction, the ventral sides of two Halteria cells fuse. Various changes in morphology then occur through maturation divisions including a decrease in the number of cirri in both cells and the loss of buccal membranelles in one of the pair and the entire oral apparatus disappears in the other. The remaining membranelles are shared between the cells at the anterior end.

Lemmermannia perform asexual reproduction (autosporation by sporangium); sexual reproduction has not been observed. Lemmermannia species perform two types of reproduction: L. tetrapedia exhibits Crucigenia-type of autosporation where the daughter coenobium rotates 45˚ relative to the cell wall of the mother coenobium; the other four species produce daughter coenobia in the same orientation as the mother coenobia. This demonstrates that in this taxon a Crucigenia-type of autosporation should not be used as a generic character.

Although it is far less dangerous than some box jellyfish species from other parts of the world, it is considered the second-most important stinging jellyfish in the Mediterranean (Pelagia noctiluca being the most important). The life history of this box jellyfish is complex. The sexes are separate and sexual reproduction takes place with the emission of gametes into the open water. After fertilisation, a planula larva forms which later develops into a cubopolyp with a few tentacles.

Audouinella, also known as black algae, is a widespread genus of red algae, found in marine and freshwater environments. It grows as small tufts of red, brown, or black hairlike filaments on any solid surface - most dramatically in freshwater on the edges of slow-growing leaves. Often tolerant of high levels of pollution, acidity, Audouinella thrives on dissolved phosphate and nitrates. It reproduces via spores, most commonly asexually, while sexual reproduction is known in rare examples .

However, it is not sexual reproduction, since no exchange of gamete occurs, and indeed no generation of a new organism: instead an existing organism is transformed. During classical E. coli conjugation the donor cell provides a conjugative or mobilizable genetic element that is most often a plasmid or transposon. Most conjugative plasmids have systems ensuring that the recipient cell does not already contain a similar element. The genetic information transferred is often beneficial to the recipient.

When the plant does reproduce sexually, it requires unrelated individuals which have different genes; it cannot fertilize itself, nor can it successfully reproduce with closely related individuals. Small population sizes that have low genetic diversity and wide distances between populations make it less likely the plant will successfully undergo sexual reproduction. The plant sometimes hybridizes with Brodiaea orcuttii. There are about 68 occurrences remaining in widely spaced locations between the San Gabriel Mountains and west-central San Diego County.

They get attached to the gut epithelial lining where they multiply rapidly by binary fission. (They are also capable of sexual reproduction by genetic hybridisation in the sandfly gut.) They then migrate back towards the anterior part of the digestive system such as pharynx and buccal cavity. This process is known as anterior station development, which is unique in Leishmania. A heavy infection of pharynx can be observed within 6 to 9 days after initial blood meal.

Ongoing research on Arabidopsis thaliana is being performed on the International Space Station by the European Space Agency. The goals are to study the growth and reproduction of plants from seed to seed in microgravity. 'Plant on a chip' devices in which A. thaliana tissues can be cultured in semi in-vitro conditions have been described. Use of these devices may aid our understanding of pollen tube guidance and the mechanism of sexual reproduction in A. thaliana.

A pine infested with A. areolatum and the Sirex woodwasp (Sirex noctilio) In their native habitat, all Amylostereum species have a minor importance as forest pests. The infestation through wood wasps does not assume greater dimensions and is, compared with other pests, almost insignificant. The infection rates are even lower during sexual reproduction via fruit bodies, as the wasps do not play a part in the process. Furthermore, the Amylostereum fungi are alone often incapable of infesting healthy trees.

P. hartmanii is capable of both heterothallic (outcrossing) and homothallic (self-fertilizing) sexual reproduction.Z Chai, Z Hu, Y Liu, Y Tang 2020. Proof of homothally of Pheopolykrikos hartmannii and details of cyst germination process Journal of Oceanology and Limnology 38 (1), 114-123 The reproductive behaviors of polykrikoids are mostly not well understood, although P. kofoidii has been studied and found to have a complex life cycle of both vegetative (asexual) and sexual reproduction complicated by its pseudocolonial structure.

Crepidula convexa follows a sequential hermaphroditism life cycle. During its life it will pass through 5 sexual phases. The immature phase where it is in the larval stage and has no need to start sexual reproduction but shows a slight rise on the right side of the neck where the phallus will later grow. Next when hatched the snail will be in what is called the “Phallus Bud” stage which is the forming of the male sexual organ and may have a “peg-like” phallus. Soon after it will have developed a full phallus and be deemed a “Male”, where it can start the sexual reproduction process and fertilize its female counterparts. Later on it will start to change and grow into a “Transitional” where the male starts to grow and loses the ability to fertilize and start to become female. Finally it will be a “Female” which will be its final sexual phase. At that point it will be able to be inseminated and lay eggs and may have a remnant of a degenerate phallus.

The cells appear brown because of melanin production. Whole genome sequencing of H. werneckii revealed a recent whole genome duplication, thought to be the only reported whole-genome duplication among ascomycetous yeasts besides the better known one in the Saccharomyces cerevisiae lineage. Based on genome sequencing of additional strains, 10 out of 12 strains have a genome that was duplicated by several hybridizations between haploid strains, yielding formed stable diploids. Apart from these hybridization events, no signs of sexual reproduction were found.

The form of sexual reproduction practiced by most placental mammals is anisogamous, requiring two kinds of dissimilar gametes, and allogamous, such that each individual only produces one of the two kinds of gametes. The smaller gamete is the sperm cell and is produced by males of the species. The larger gamete is the ovum and is produced by females of the species. Under this scheme, fertilization requires two gametes, one from an individual of each sex, in order to occur.

European honey bee carrying pollen in a pollen basket back to the hive Pollination is the process by which pollen is transferred in the reproduction of plants, thereby enabling fertilisation and sexual reproduction. Most flowering plants require an animal to do the transportation. While other animals are included as pollinators, the majority of pollination is done by insects. Because insects usually receive benefit for the pollination in the form of energy rich nectar it is a grand example of mutualism.

At maturity, the gametophyte produces gametes by mitosis, which does not alter the number of chromosomes. Two gametes (originating from different organisms of the same species or from the same organism) fuse to produce a diploid zygote, which develops into a diploid sporophyte. This cycle, from gametophyte to sporophyte (or equally from sporophyte to gametophyte), is the way in which all land plants and many algae undergo sexual reproduction. The relationship between the sporophyte and gametophyte varies among different groups of plants.

The plant is more abundant and undergoes sexual reproduction more often in open areas where it receives at least partial sun. It is often found with Phlox glaberrima, a common flower of the prairie which is now considered an indicator of potential appropriate habitat for the Clematis. The main threat to this species is the destruction, degradation, and modification of its habitat. Some populations known to have existed have since been destroyed by such activities as installation of gas pipelines and road resurfacing.

The areoles may be flat or convex. Its sexual reproduction structures (apothecia) are a 0.35–1.0 mm-wide disc, darker yellow than the thallus, rimmed with thallus-like tissue lecanorine, flat but becoming convex with age. Lichen spot tests are K+ reddish, KC-, and C-. It produces calycin, pulvinic acid, pulvinic dilactone and vulpinic acid as secondary metabolites. In California, it prefers growing on granite, but can also be found on wood (rarely on bark) and other kinds of rock.

A probable reason for the view that sex may not be fundamental to eukaryotes was that sexual reproduction previously appeared to be lacking in certain human pathogenic single-celled eukaryotes (e.g. Giardia) that diverged from early ancestors in the eukaryotic lineage. In addition to the evidence cited above for recombination in Giardia, Malik et al. reported that many meiosis specific genes occur in the Giardia genome, and further that homologs of these genes also occur in another unicellular eukaryote, Trichomonas vaginalis.

For a bacterium to bind, take up, and recombine exogenous DNA into its chromosome, it must enter a special physiological state referred to as competence (see Natural competence). Sexual reproduction in early single-celled eukaryotes may have evolved from bacterial transformation,Bernstein H, Bernstein C, Michod RE. (2012) "DNA Repair as the Primary Adaptive Function of Sex in Bacteria and Eukaryotes". Chapter 1, pp. 1–50, in DNA Repair: New Research, Editors S. Kimura and Shimizu S. Nova Sci. Publ.

Cnidarian sexual reproduction often involves a complex life cycle with both polyp and medusa stages. For example, in Scyphozoa (jellyfish) and Cubozoa (box jellies) a larva swims until it finds a good site, and then becomes a polyp. This grows normally but then absorbs its tentacles and splits horizontally into a series of disks that become juvenile medusae, a process called strobilation. The juveniles swim off and slowly grow to maturity, while the polyp re-grows and may continue strobilating periodically.

A parthenogenetic species can undergo a more rapid population increase than a sexual species because all parthenotes are female and produce offspring, while in sexual species half of all individuals are males and do not give birth to offspring. Additionally, laboratory experiments have revealed that even obligate parthenotes retain the capability of incorporating new genetic material through sexual reproduction to form new parthenogenetic lineages, and the ability to outcross on occasion may explain the lengthy evolutionary persistence of some parthenogenetic species.

Radiocarbon dating indicates that some Lophelia reefs in the waters off North Carolina may be 40,000 years old, with individual living coral bushes as much as 1,000 years old. Lophelia pertusa The colony grows by the budding off of new polyps. Living polyps are present on the edges of dead coral and fragmentation of coral colonies provides one form of asexual reproduction. Each colony is either male or female and sexual reproduction occurs when these liberate sperm and oocytes into the sea.

If its absence implies the species has no males, then perhaps its "sexual" reproduction may be a case of the above-described process of regeneration combining cells separated from two separate organisms into one. Due to the possibility of its cloning itself by asexual propagation without limit, the life span of Placozoa is infinite; in the laboratory, several lines descended from a single organism have been maintained in culture for an average of 20 years without the occurrence of sexual processes.

As predicted, sexual reproduction dominates in shallow water, due to its advantages in parasite resistance. Asexual reproduction is dominant in the deeper water of lakes, as the scarcity of parasites means that the advantages of resistance are outweighed by the costs of sexual reproduction.Fox J., Dybdahl M., Jokela J., Lively C. (1996). Genetic structure of coexisting sexual and clonal subpopulations in a freshwater snail (Potamopyrgus antipodarum). Evolution. 50 (4): 1541-1548 Each female can produce between 20 and 120 embryos.

Species of Bangia undergo a heteromorphic alternation of generation life cycle in which the haploid generation is dominant. Reproduction can be either sexual or asexual; sexual plants occur mainly during the cold season of the year, while at other times the thalli often bear monosporangia only. Bangia, like all Rhodophytes, lack motile sperm and so depend upon water currents to transport their gametes to the trichogyne (receptive area of the female gamete or carpogonium). All sexual reproduction in rhodophytes is oogamous.

In areas where the pathogen is newly introduced, the fungal population is mostly clonal because there are fewer mating types within the population and therefore sexual reproduction may be lower. Pitch Canker infects nearly all pine tree species including longleaf pine, short leaf pine, and eastern white pine. This disease continues to be a problem in nurseries and has been reported in other countries. A major problem in Florida is that artificial replanting of pines may be contributing to high disease incidences.

And perithecia which are shaped like flasks that enclose a spore producing layer with a hole at the top ( Brodo, Sharnoff, and Sharnoff). Since sexual reproduction is inefficient, lichen will reproduce asexually by vegetative reproduction when possible. Foliose lichen use isidia which are cylindrical finger like protuberances from the upper cortex in which algal and fungal tissue is incorporated into. They are easily broken off and transported by wind where they will relocate and propagate forming a new lichen (Easton pg. 62).

The life history strategies of foliose lichens is directly related to their surrounding communities. Studies have shown a shift from sexual to vegetative communities with changes in environment. It was found that if sexual reproduction is important for allelic diversity then habitats with high levels of disturbance would have species with rapid life cycles and high reproductive output to better respond to the changing habitat. Three types of foliose saxicolous lichen were chosen for a study because they each dominated different communities.

Insemination is the introduction of sperm into a female animal’s reproductive system for the purpose of impregnating or fertilizing the female for sexual reproduction. The sperm is introduced into the uterus of a mammal or the oviduct of an oviparous (egg-laying) animal. In mammals, insemination normally occurs during sexual intercourse or copulation, but insemination can take place in other ways, such as by artificial insemination. In humans, the act and form of insemination has legal, moral and interpersonal implications.

The polyps also undergo asexual reproduction to create more polyps; parts of each polyp will eventually metamorphose into ephyrae, which range between 1.7 and 4.2 mm in diameter. Young medusa take 8–10 weeks to reach an initial diameter of 3 cm, and then will grow by approximately 3–4 cm per week until reaching their final adult size. Gradually, the medusa develop with an average final diameter of approximately 35 cm. Sexual reproduction between adult medusa typically occurs between August and October.

This results in a single cell with two nuclei, known as pronuclei. The pronuclei then fuse together in a well regulated process known as karyogamy. This creates a diploid cell known as a zygote, or a zygospore, which can then enter meiosis, a process of chromosome duplication, recombination, and cell division, to create four new haploid gamete cells. One possible advantage of sexual reproduction is that it results in more genetic variability, providing the opportunity for adaptation through natural selection.

P. muellerae is a non- zooxanthellate coral; it does not have a symbiotic relationship with microscopic dinoflagellates as do most corals, instead obtaining all its nutrition from the planktonic organisms caught by the polyps. Asexual reproduction by budding increases the size of the colony. Sexual reproduction has not been observed in this species, but the fact that the coral has a widespread distribution suggests that it is likely to occur. This coral is sometimes parasitized by the barnacle Megatrema anglicum.

For example, the common intestinal parasite Giardia lamblia was once considered to be a descendant of a protist lineage that predated the emergence of meiosis and sex. However, G. lamblia was recently found to have a core set of genes that function in meiosis and that are widely present among sexual eukaryotes. These results suggested that G. lamblia is capable of meiosis and thus sexual reproduction. Furthermore, direct evidence for meiotic recombination, indicative of sex, was also found in G. lamblia.

Some individual fungal colonies can reach extraordinary dimensions and ages as in the case of a clonal colony of Armillaria solidipes, which extends over an area of more than 900ha (3.5 square miles), with an estimated age of nearly 9,000years. The apothecium—a specialized structure important in sexual reproduction in the ascomycetes—is a cup-shaped fruit body that is often macroscopic and holds the hymenium, a layer of tissue containing the spore-bearing cells.Alexopoulos et al., pp. 204–205.

The life history of diatoms includes both vegetative and sexual reproduction, though the sexual stage is not yet documented in this species. Although it is symmetric only along the apical axis, typical of gomphonemoid diatoms, it is a cymbelloid, which are typically symmetric along both primary axes. Cells contain a raphe, which allows them to move on surfaces, and an apical porefield, through which a mucopolysaccharide stalk is secreted. The stalk can attach to rocks, plants, or other submerged surfaces.

There are several advantages of vegetative reproduction, mainly that the produced offspring are clones of their parent plants. If a plant has favorable traits, it can continue to pass down its advantageous genetic information to its offspring. It can be economically beneficial for commercial growers to clone a certain plant to ensure consistency throughout their crops. Vegetative propagation also allows plants to avoid the costly and complex process of producing sexual reproduction organs such as flowers and the subsequent seeds and fruits.

In genetic algorithms and evolutionary computation, crossover, also called recombination, is a genetic operator used to combine the genetic information of two parents to generate new offspring. It is one way to stochastically generate new solutions from an existing population, and analogous to the crossover that happens during sexual reproduction in biology. Solutions can also be generated by cloning an existing solution, which is analogous to asexual reproduction. Newly generated solutions are typically mutated before being added to the population.

At the beginning of the sexual reproduction cycle of B. trispora, the initial step is the production of carotenes from carotenoids. Carotenes are further processed by carotene oxygenase, which is encoded in the tsp3 gene of the B. trispora, to produce TSA. TSA is produced by both of the mating types: (+) and (-) strains, and it is copiously produced especially when compatible mycelia are grown together. As these two different sex types produce TSA, they sense sexually complementary cells and form gametangia.

Reproduction is mostly by basal laceration, a form of asexual reproduction. The sea anemone crawls along a hard surface and pieces of tissue become detached and grow into new individuals. However, it is likely that sexual reproduction sometimes takes place, as otherwise this species would be unlikely to be so widely dispersed. Amphianthus dohrnii was at one time common in both the Mediterranean and the English Channel, but it seems now to be absent from the former and increasingly rare in the latter.

Algae constitute a polyphyletic group since they do not include a common ancestor, and although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria. Diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a wide range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction.

Rhodophyta, Chlorophyta, and Heterokontophyta, the three main algal divisions, have lifecycles which show considerable variation and complexity. In general, an asexual phase exists where the seaweed's cells are diploid, a sexual phase where the cells are haploid, followed by fusion of the male and female gametes. Asexual reproduction permits efficient population increases, but less variation is possible. Commonly, in sexual reproduction of unicellular and colonial algae, two specialized, sexually compatible, haploid gametes make physical contact and fuse to form a zygote.

Hepatozoon species in the blood of reptiles Members of the genus Hepatozoon possess particularly complex lifecycles which vary considerably among species. Sexual reproduction and sporogenic development occur within the haemocoel of the invertebrate host, which is subsequently consumed by the vertebrate host. The sporozoites then migrate to the liver of the vertebrate, where they undergo multiple fission (asexual reproduction) to produce merozoites. The meronts are released into the bloodstream where they form gametocytes, the final stage of development within the vertebrate host.

Lophiostoma compressum from Oslo Herbarium by Mathias Andreasen "Lophiostomataceae of Norway" The fruit body of the sexual reproduction (teleomorph) are characterized as having immersed to erumpent ascocarp with a slitlike ostiole; unequal thickness of peridium, which is broader laterally at the base. The shape of asci are mostly clavate and their morphology are bitunicate. Ascospores are 1- to several septate, hyaline to dark brown ascospores with terminal appendages or mucous sheath. The genus does also reproduce asexually (anamorph), creating conidia and conidiospores.

A nuptial gift is a nutritional gift given by one partner in some animals' sexual reproduction practices. Formally, a nuptial gift is a material presentation to a recipient by a donor during or in relation to sexual intercourse that is not simply gametes in order to improve the reproductive fitness of the donor. Often, such a gift will improve the fitness of the recipient as well. This definition implies neutral gifts, costly gifts and beneficial gifts regarding the fitness of the recipient.

Pawpaws spread locally primarily by root suckers; sexual reproduction by seed does also occur, but at a fairly low rate. Pawpaw flowers are insect-pollinated, but fruit production is sometimes limited as few if any pollinators are attracted to the flower's faint, or sometimes nonexistent scent. The flowers produce an odor similar to that of rotting meat to attract blowflies or carrion beetles for cross-pollination. Other insects that are attracted to pawpaw flowers include scavenging fruit flies, carrion flies, and beetles.

The pelvic bones of modern male cetaceans are more massive, longer, and larger than those of females. Due to the sexual dimorphism displayed, they were most likely involved in supporting male genitalia that remain hidden behind abdominal walls until sexual reproduction occurs. Early archaeocetes such as Pakicetus had the nasal openings at the end of the snout, but in later species such as Rodhocetus, the openings had begun to drift toward the top of the skull. This is known as nasal drift.

Second, sex acts to bring together currently deleterious mutations to create severely unfit individuals that are then eliminated from the population (i.e. sex aids in the removal of deleterious genes). However, in organisms containing only one set of chromosomes, deleterious mutations would be eliminated immediately, and therefore removal of harmful mutations is an unlikely benefit for sexual reproduction. Lastly, sex creates new gene combinations that may be more fit than previously existing ones, or may simply lead to reduced competition among relatives.

Those animals with currently high oestrogen levels assume "feminine" sexual roles. Lizards that perform the courtship ritual have greater fecundity than those kept in isolation due to an increase in hormones triggered by the sexual behaviours. So, even though asexual whiptail lizards populations lack males, sexual stimuli still increase reproductive success. From an evolutionary standpoint these females are passing their full genetic code to all of their offspring rather than the 50% of genes that would be passed in sexual reproduction.

Only adult B. carambolae are capable of mating through sexual reproduction, although the larval stage is capable of producing pheromones to a certain degree. Male B. carambolae are strongly attracted to methyl eugenol (ME), which is a secondary plant compound found worldwide. As they feed on this compound, they convert it into a phenylpropanoid known as (E)-coniferyl alcohol (ECF). This new compound is stored in the rectal gland of the male, ready to be released as a sex pheromone during courtship.

Members of the Hemitrichia follow the typical plasmodial slime mold life cycle, which exhibits two main stages as well as possible sexual reproduction. Slime molds spend a period of their life cycle as a myxameoba or a swarm cells. These cells are able to exist as either amoeba or flagellates depending on the conditions the cell experiences, and are hence known as amoeboflagellates. The amoeba form is preferred for terrestrial environments, while the swimming ability of flagella is preferred in a wet environment.

The plant is threatened by its small numbers, alterations in the hydrology of its riparian habitat, and habitat fragmentation. Populations are isolated from one another, reducing the frequency of its rare sexual reproduction even further. Populations are small; though the plant is adapted to a regime of flooding, unusually large floods have the potential to wipe out small populations. The invasion of introduced plant species, including the shrub's relative, Spiraea japonica (Japanese spiraea), may be a threat because of competition.

An olfactory cue is a chemical signal received by the olfactory system that represents an incoming signal received through the nose. This allows humans and animals to smell the chemical signal given off by a physical object. Olfactory cues are extremely important for sexual reproduction, as they trigger mating behavior in many species, as well as maternal bonding and survival techniques such as detecting spoiled food. The results of receiving and processing this information is known as the sense of smell.

Brachymeiosis was a hypothesized irregularity in the sexual reproduction of ascomycete fungi, a variant of meiosis following an "extra" karyogamy (nuclear fusion) step. The hypothesized process would have transformed four diploid nuclei into eight haploid ones. The current scientific consensus is that brachymeiosis does not occur in any fungi. According to the current understanding, ascomycetes reproduce by forming male and female organs (antheridia/spermatia and ascogonia), transferring haploid nuclei from the antheridium to the ascogonium, and growing a dikaryotic ascus containing both nuclei.

Colpophyllia natans is a hermaphroditic broadcast spawner, releasing large numbers of gametes synchronously to aid fertilisation. Each individual polyp spawns both eggs and sperm, having the reproductive capabilities of both the male and female sexes. Following fertilisation, the zygote becomes a microscopic larva called a planula, which, upon swimming to suitable substrate, will anchor and establish a new colony. This method of sexual reproduction has a high rate of failure in several of its stages and few new colonies successfully grow.

The slow modifying effect of succession and similar shifts in the composition of the system can, however, not be neglected in the long run. Overall, life's object's capabilities of self-perpetuation are always accompanied by evolution, a perfect steady state of the biological system is never reached. Sexual reproduction is also a form of imperfect self-replication and thus imperfect self-perpetuation because of recombination and mutation. Organisms are not like self-replicating machine but amass random modifications from generation to generation.

During the process of meiosis, male Cyclotella cells release sperm and the female Cyclotella cells develop and egg from within the two valves. Following fertilization of the egg, a zygote is formed from the union of the two gametes. The zygote then develops into an auxophore (2n). Once sexual reproduction is complete, the diameter of the offspring is larger and beyond the threshold once again, allowing for the production of another few hundred generations through the asexual division of auxophores.

Sex-determining polyphenisms allow a species to benefit from sexual reproduction while permitting an unequal gender ratio. This can be beneficial to a species because a large female-to-male ratio maximizes reproductive capacity. However, temperature-dependent sex determination (as seen in crocodiles) limits the range in which a species can exist, and makes the species susceptible to endangerment by changes in weather pattern. Temperature-dependent sex determination has been proposed as an explanation for the extinction of the dinosaurs.

An interspecific semiochemical that is beneficial to both interacting organisms, the emitter and receiver, e.g. floral synomone of certain Bulbophyllum species (Orchidaceae) attracts fruit fly males (Tephritidae: Diptera) as pollinators. In this true mutualistic inter-relationship, both organisms gain benefits in their respective sexual reproduction - i.e. orchid flowers are pollinated and the Dacini fruit fly males are rewarded with a sex pheromone precursor or booster; and the floral synomones, also act as rewards to pollinators, are in the form of phenylpropanoids (e.g.

The fertilized cell contains all the nuclear and organellar materials from both gametes until the onset of meiosis, which occurs 24 hours after the insect-host molts and triggers the digestion of one flagellum and one centriole from one gamete and the axostyles of both gametes. After meiosis is complete, the remaining centriole duplicates producing new flagella and axostyles. In mitotic cell division, only the axostyle is digested and renewed. There are some subtle differences in sexual reproduction between Saccinobaculus species.

Unlike in higher animals, where parthenogenesis is rare, asexual reproduction may occur in plants by several different mechanisms. The formation of stem tubers in potato is one example. Particularly in arctic or alpine habitats, where opportunities for fertilisation of flowers by animals are rare, plantlets or bulbs, may develop instead of flowers, replacing sexual reproduction with asexual reproduction and giving rise to clonal populations genetically identical to the parent. This is one of several types of apomixis that occur in plants.

Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells. This takes place through a pilus. It is a mechanism of horizontal gene transfer as are transformation and transduction although these two other mechanisms do not involve cell-to-cell contact. Classical E. coli bacterial conjugation is often regarded as the bacterial equivalent of sexual reproduction or mating since it involves the exchange of genetic material.

In its native Asian habitat, a third winged generation called sexupera occurs; although this generation's sexual reproduction requires a species of spruce not found in the Eastern United States, and therefore dies, Between 100 and 300 eggs are laid by each individual in the woolly egg sacs beneath the branches. Larvae emerge in spring and can spread on their own or with the assistance of wind, birds, or mammals. In the nymph stage, the adelgid is immobile and settles on a single tree.

Sexual propagation yields 50% male seedlings, which are unproductive. As there is no reliable method of determining plant sex before flowering in the sixth to eighth year, and sexual reproduction bears inconsistent yields, grafting is the preferred method of propagation. Epicotyl grafting (a variation of cleft grafting using seedlings), approach grafting, and patch budding have proved successful, with epicotyl grafting being the most widely adopted standard. Air layering is an alternative though not preferred method because of its low (35–40%) success rate.

A mule is a sterile hybrid of a male donkey and a female horse. Mules are smaller than horses but stronger than donkeys, making them useful as pack animals. In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in blending inheritance), but can show hybrid vigour, sometimes growing larger or taller than either parent.

In diploid eukaryotes, this is a consequence of the system of sexual reproduction, where mutant alleles get partially shielded, for example, by genetic dominance. Microorganisms, with their huge populations, also carry a great deal of genetic variability. The first experimental evidence of the pre- adaptive nature of genetic variants in microorganisms was provided by Salvador Luria and Max Delbrück who developed the Fluctuation Test, a method to show the random fluctuation of pre-existing genetic changes that conferred resistance to bacteriophages in Escherichia coli.

It is also assumed that the control line will be free of mutations: since the organisms within the control line are able to freely sexually reproduce, it is thought that most mutations that arise within individuals will be relatively quickly lost during sexual reproduction. Furthermore, since the organisms in an MA experiment are raised under relaxed natural selection, it is assumed that all mutations that arise have arisen randomly, and become fixed or lost at random, in the absence of any selective pressure exerted by the environment.

Single-progeny descent is only possible if the organism being studied is capable of asexual reproduction or self-fertilization. In cases where an organism is only capable of sexual reproduction (such as Drosophila melanogaster, which was the species used in many early MA experiments), organisms with balancer chromosomes are used. In MA experiments involving an obligate sexually reproducing species such as Drosophila, mutations are accumulated on only one of a pair of homologous chromosomes. The other homologous chromosome is a modified so-called balancer chromosome.

Nägler had also stated that when exposed to dry conditions for long periods of time, the trophozoites did not encyst, further supporting the hypothesis that the cysts are used for sexual reproduction, and not as protection from desiccation. Sappinia species also undergo asexual reproduction, as described by Nägler in 1908. First the two nuclei divide, and two pairs of nuclei are formed in parallel configuration. Then the nuclei cross and become anti- parallel, so that each daughter cell receives half of each of the two nuclei.

'Ancient asexuals': Bdelloid rotifers are assumed to have reproduced without sex for many millions of years. Males are absent within the species, and females reproduce only by parthenogenesis. Recent transitions: Loss of sexual reproduction can be inherited in a simple Mendelian fashion in the monogonont rotifer Brachionus calyciflorus: This species can normally switch between sexual and asexual reproduction (cyclical parthenogenesis), but occasionally gives rise to purely asexual lineages (obligate parthenogens). These lineages are unable to reproduce sexually due to being homozygous for a recessive allele.

Most animals and many plants are diploid for most of their lifespan, with the haploid form reduced to single cell gametes such as sperm or eggs. Although they do not use the haploid/diploid method of sexual reproduction, bacteria have many methods of acquiring new genetic information. Some bacteria can undergo conjugation, transferring a small circular piece of DNA to another bacterium. Bacteria can also take up raw DNA fragments found in the environment and integrate them into their genomes, a phenomenon known as transformation.

Bodies are created and discarded, but good genes live on as replicas of themselves, a result of a high-fidelity copy process typical of digital encoding. Through meiosis (sexual reproduction), genes share bodies with different companion genes in successive generations. Thus genes can be said to flow in a river through geological time. Even though genes are selfish, over the long run every gene needs to be compatible with all other genes in the gene pool of a population of organisms, to produce successful organisms.

Many populations don't develop seeds. Although no publication attests to sexual reproduction, it can not be totally excluded, since some grains pollen are viable. Finally, parthenogenesis or outcrossing with other gageas are possible, especially as the hybridization is observed in the genus, however, not with Gagea spathacea as parent. A study of the European populations shows the exclusivity of vegetative reproduction. 138 samples from 52 populations covering most of the species’ distribution range: Netherlands (2), Belgium (1), Sweden (4), Italy (2), Russia (2) and Germany (41).

Like other yeasts also the species within the genus Ogataea are single-celled or built pseudohyphae of only a few elongated cells, true hyphae are not formed. They are able to reproduce via a sexual and an asexuel reproduction. The latter one happens with a cell division by multilateral budding on a narrow base with spherical to ellipsoidal budded cells. In the sexual reproduction the asci are deliquescent and may be unconjugated or show conjugation between a cell and its bud or between independent cells.

The life cycle of P. skrjabini involves three hosts. The first intermediate host is a mollusk (typically a snail), the second intermediate host is a crustacean (typically a crab), and the definitive host is a mammal such as a dog, cat, or a human. Among others, freshwater crab species of the genus Nanhaipotamon are known to be second intermediate hosts for P. skrjabini. The mammal is the definitive host because it is the site where sexual reproduction occurs and adult P. skrjabini flukes develop.

Canna fruit (green) and ripe seed pods Canna fruits Seeds are produced from sexual reproduction, involving the transfer of pollen from the stamen of the pollen parent onto the stigma of the seed parent. In the case of Canna, the same plant can usually play the roles of both pollen and seed parents, technically referred to as a hermaphrodite. However, the cultivars of the Italian Group and triploids are almost always seed sterile, and their pollen has a low fertility level. Mutations are almost always totally sterile.

The first biological law is egoistic and related with withdrawal from reality (escape, destruction of reality etc.). The second biological law is altruistic and requires turning towards the reality (sexual reproduction requires union with the partner). In case of humans, the connection between the goals of various everyday actions and two biological laws is less direct, nevertheless these laws still motivate us. Humans are able to project themselves into the future, think abstractly and consciously and therefore their goals may possess transcendent and symbolic character.

Sexual reproduction is via broadcast spawning of gametes into the water column once each year in August or September. Individual colonies are both male and female (simultaneous hermaphrodites) and will release millions of gametes. The coral larvae (planula) live in the plankton for several days until finding a suitable area to settle; unfortunately, very few larvae survive to settle and metamorphose into new colonies. The preponderance of asexual reproduction in this species raises the possibility that genetic diversity in the remnant populations may be very low.

B. affinis consumes the nectar and pollen of a variety of nototrobic plant species, including Lobelia siphilitica, Linaria vulgaris, and Antirrhinum majus. Dicentra cucullaria, a flowering plant, is particularly dependent on members of the B. affinis for sexual reproduction. In fact, the flower structure and mechanism by which it is pollinated indicate that it is adapted for foragers such as B. affinis, which can separate the outer and inner petals of the flower. Members then use their front legs to expose the stigma, stamen, and anthers.

Koinophilia might also contribute to the maintenance of sexual reproduction, preventing its reversion to the much simpler asexual form of reproduction. The koinophilia hypothesis is supported by the findings of Judith Langlois and her co-workers. They found that the average of two human faces was more attractive than either of the faces from which that average was derived. The more faces (of the same gender and age) that were used in the averaging process the more attractive and appealing the average face became.

Third, recessive deleterious alleles will be "masked" by heterozygosity, and so in a dominant-recessive trait, heterozygotes will not be selected against. When recessive deleterious alleles occur in the heterozygous state, where their potentially deleterious expression is masked by the corresponding wild-type allele, this masking phenomenon is referred to as complementation (see complementation (genetics)). In general, sexual reproduction in eukaryotes has two fundamental aspects: genetic recombination during meiosis, and outcrossing. It has been proposed that these two aspects have two natural selective advantages respectively.

Fungi are classified primarily based on the structures associated with sexual reproduction, which tend to be evolutionarily conserved. However, many fungi reproduce only asexually, and cannot easily be classified based on sexual characteristics; some produce both asexual and sexual states. These problematic species are often members of the Ascomycota, but a few of them belong to the Basidiomycota. Even among fungi that reproduce both sexually and asexually, often only one method of reproduction can be observed at a specific point in time or under specific conditions.

The hormonal influences of sexual motivation are much more clearly understood for nonprimate females. Suppression of estrogen receptors in the ventromedial nucleus of the hypothalamus in female rats has been observed to reduce female proceptivity and receptivity. Proceptivity and receptivity in the female rat are indicators of sexual motivation, thus indicating a direct relationship between estrogen levels and sexual motivation. In addition, female rats receiving doses of estrogen and progesterone were more likely to exert effort at gaining sexual reproduction attention from a male rat.

In culture, colonies of U. reesii grow moderately fast and are yellowish-white to buff in colour, are flat and dense in shape, and range from velvety to powdery in texture. Arthroconidia of U. reesii tend to be broad compared to most Malbranchea, ranging from approximately 2.5-3.5 μm x 3.5-6 μm in size. As a heterothallic species, two compatible "sexes" are required for sexual reproduction to occur. As with other members of the genus Uncinocarpus, U. reesii can develop hooked (uncinate) appendages on vegetative hyphae.

Though cell reproduction that uses mitosis can reproduce eukaryotic cells, eukaryotes bother with the more complicated process of meiosis because sexual reproduction such as meiosis confers a selective advantage. Notice that when meiosis starts, the two copies of sister chromatids number 2 are adjacent to each other. During this time, there can be genetic recombination events. Information from the chromosome 2 DNA gained from one parent (red) will transfer over to the chromosome 2 DNA molecule that was received from the other parent (green).

Taiaroa tauhou is a solitary coral that reproduces solely by means of sexual reproduction. It may be a hermaphrodite, as one individual examined contained both eggs and spermaries (sperm producing organs), but other individuals only contained eggs or were exclusively male. It is unclear whether the gonads in the bisexual individual were attached to the body wall. It may be that the males liberate spermaries which are ingested by the females, resulting in internal fertilisation, and this would mean that the animals are not hermaphroditic.

Whether Tetraphis pellucida as a colony exhibits asexual reproduction or sexual reproduction is determined based on shoot density. At low densities (less than 70 shoots per cm^2) there are no sporophytes and solely possess gemmiferous shoots. At a density over 70 shoots/cm^2 gametophores begin to appear, by 190 shoots/cm^2 there are no gemmiferous shoots. Initially archegoniophores(gametophyte shoots bearing archegonia) out number antheridiophores (gametophyte shoots bearing antheridia), but as the density increases more the antheridiophores greatly outnumber the archegoniophores.

Heitman's research has largely focused on the cell biology and sexual cycle of the pathogenic fungus Cryptococcus. His group described a previously unknown form of sexual reproduction in Cryptococcus species that allows sexual recombination between individuals of the same mating type. Heitman's group has also had a long-standing interest in fungal evolution, describing how cellular processes such as sexual recombination and RNA interference are changed in different fungal lineages, as well as the expansion of the geographic range of the emerging pathogen Cryptococcus gattii.

At room temperature (25–30 °C), colonies of B. ranarum show very rapid growth and are able to reach a diameter of 75–80 mm in a week on suitable growth media. The favored carbohydrate source of this fungus is glucose that can stimulate the growth of its mycelium. Generally, asexual reproduction is favored by glucose and sexual reproduction is favored by acid amines. Primary asexual spores are singly formed on the apices of unbranched hyphae and will then be discharged to form ballistic spores.

Oospores of Hyaloperonospora parasitica, agent of the downy mildew (in the middle) An oospore is a thick-walled sexual spore that develops from a fertilized oosphere in some algae, fungi, and oomycetes. They are believed to have evolved either through the fusion of two species or the chemically- induced stimulation of mycelia, leading to oospore formation. In Oomycetes, oospores can also result from asexual reproduction, by apomixis. These are found in Fungi as the sexual spores; these help in the sexual reproduction of Fungi.

Some protists reproduce sexually using gametes, while others reproduce asexually by binary fission. Some species, for example Plasmodium falciparum, have extremely complex life cycles that involve multiple forms of the organism, some of which reproduce sexually and others asexually. However, it is unclear how frequently sexual reproduction causes genetic exchange between different strains of Plasmodium in nature and most populations of parasitic protists may be clonal lines that rarely exchange genes with other members of their species. Eukaryotes emerged in evolution more than 1.5 billion years ago.

Besides regular sexual reproduction with meiosis, certain fungi, such as those in the genera Penicillium and Aspergillus, may exchange genetic material via parasexual processes, initiated by anastomosis between hyphae and plasmogamy of fungal cells.Jennings and Lysek, pp. 114–115. The frequency and relative importance of parasexual events is unclear and may be lower than other sexual processes. It is known to play a role in intraspecific hybridization and is likely required for hybridization between species, which has been associated with major events in fungal evolution.

Conversely, "The Loves of Plants" was focused on uniting nature with man through the appreciation of botany. In it, Darwin encourages humans to study botany because plants are a part of the same natural world as man. He also argues that sexual reproduction gives rise to phenotypic change (which his grandson would later incorporate into his own theory of evolution put forth in On the Origin of Species).266.974x266.974pxIn 1794, Erasmus Darwin also wrote Zoonomia, another book of verse, this time dealing with human physiology.

Sexual reproduction cycle of basidiomycetes Unlike animals and plants which have readily recognizable male and female counterparts, Basidiomycota (except for the Rust (Pucciniales)) tend to have mutually indistinguishable, compatible haploids which are usually mycelia being composed of filamentous hyphae. Typically haploid Basidiomycota mycelia fuse via plasmogamy and then the compatible nuclei migrate into each other's mycelia and pair up with the resident nuclei. Karyogamy is delayed, so that the compatible nuclei remain in pairs, called a dikaryon. The hyphae are then said to be dikaryotic.

It appears that isogamy was the first stage of sexual reproduction. In several lineages (plants, animals), this form of reproduction independently evolved to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is very much larger than the male and has no ability to move. There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction.Dusenbery, David B. (2009).

The haploid number (n) refers to the total number of chromosomes found in a gamete (a sperm or egg cell produced by meiosis in preparation for sexual reproduction). Under normal conditions, the haploid number is exactly half the total number of chromosomes present in the organism's somatic cells. For diploid organisms, the monoploid number and haploid number are equal; in humans, both are equal to 23. When a human germ cell undergoes meiosis, the diploid 46-chromosome complement is split in half to form haploid gametes.

The freshwater alga Spirogyra Spirogyra can reproduce both sexually and asexually. In vegetative reproduction, fragmentation takes place, and Spirogyra simply undergoes intercalary cell division to extend the length of the new filaments. Sexual reproduction is of two types: # Scalariform conjugation requires association of two or more different filaments lined side by side, either partially or throughout their length. One cell each from opposite lined filaments emits tubular protuberances known as conjugation tubes, which elongate and fuse to make a passage called the conjugation canal.

In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined.

Checkpoint regulation plays an important role in an organism's development. In sexual reproduction, when egg fertilization occurs, when the sperm binds to the egg, it releases signalling factors that notify the egg that it has been fertilized. Among other things, this induces the now fertilized oocyte to return from its previously dormant, G0, state back into the cell cycle and on to mitotic replication and division. p53 plays an important role in triggering the control mechanisms at both G1/S and G2/M checkpoints.

Proposed nomenclature for mating type genes of filamentous Ascomycetes. Fungal Genetics and Biology 31:1-5 Genotyping of S. turcica populations has shown that sexual reproduction in a given population might be commonplace, extremely rare, or anywhere in between. Genotyping of 264 isolates of S. turcica from temperate and tropical regions found that tropical populations had very high genetic diversity, an equal proportion of the two mating types, and low amounts of linkage disequilibrium between different genetic loci, all suggestive of frequent sexual mating and recombination.

In the US, wild and managed bees contribute to $15 billion in crop value. As of 2009, the amount of hives in the USA has been shrinking at a steady pace since 1961. Pollinators participate in the sexual reproduction of many plants by ensuring cross- pollination, essential for some species and a major factor in ensuring genetic diversity for others. Since plants are the primary food source for animals, the possible reduction or disappearance of pollinators has been referred to as an "armageddon" by some journalists.

Unfortunately, the sexual reproduction of these plants are relatively unknown due to lack of research and can vary from species to species. In autumn, from August to November fruiting occurs. For the rest of the year, the winter months, the species will break up, dry out and decay but it has been seen that there are cases where it can survive. The reason these plants are scattered all over the globe is because Ludwigia can be generated during all seasons just from fragments of stems or rhizomes.

Birds are social, communicating with visual signals, calls, and songs, and participating in such behaviours as cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are polygynous (one male with many females) or, rarely, polyandrous (one female with many males). Birds produce offspring by laying eggs which are fertilised through sexual reproduction.

A Sex education curriculum is a sex education program encompassing the methods, materials, and assessments exercised to inform individuals of the issues relating to human sexuality, including human sexual anatomy, sexual reproduction, sexual intercourse, reproductive health, emotional relations, reproductive rights and responsibilities, abstinence, birth control, and other aspects of human sexual behavior. Common sex education curricula include an abstinence-only approach, as well as a comprehensive approach, implemented in academia via the Internet, peer education, visual media, games, health care organizations, and school instruction.

The genus was first described by Noren and Moestrup in 1999 and was isolated off the west coast of Sweden. The discovery was made through the collection of dinoflagellates Dinophysis on the Swedish West Coast, which were found to contain round bodies that were assumed to be products of sexual reproduction. After preservation in the refrigerator for two weeks, the dinoflagellates had all died but what had remained were the round bodies. These were further found to be sporangia of parasitic protist, later described as Parvilucifera infectans.

In recognition of her own standpoint, Smith shed light on the fact that sociology was lacking in the acknowledgment of standpoint. At this point, the methods and theories of sociology had been formed upon and built in a male-dominated social world, unintentionally ignoring the women's world of sexual reproduction, children, and household affairs. Women’s duties are seen as natural parts of society, rather than as an addition to culture. Smith believed that asking questions from a female’s perspective could provide insight into social institutions.

Similarly, during the night hours (non-light hours) when zooplankton populations are low, these eels will return to their burrows and cap them off while they sleep. Other key characteristics of this genus includes colonial living species, sometimes with a density of up to 40 individuals in a meter- by-meter territory, as well as a metamorphosis stage between the egg stage and adulthood. Colonial living aides in evasion of predators and plays a vital role in their sexual reproduction (see section labelled “Reproduction”).

Ovary of a marine fish and its parasite, the nematode Philometra fasciati Birds have only one functional ovary (the left), while the other remains vestigial. Ovaries in females are analogous to testes in males, in that they are both gonads and endocrine glands. Ovaries of some kind are found in the female reproductive system of many animals that employ sexual reproduction, including invertebrates. However, they develop in a very different way in most invertebrates than they do in vertebrates, and are not truly homologous.

This permits the reshuffling of hereditary characteristics, as in other types of sexual reproduction. Conjugation is immediately followed by binary fission of the two conjugants. In Blepharisma, as in some other ciliates, chemical substances called gamones are used to induce conjugation by stimulating interaction between compatible mating partners. Although clonal cells of Blepharisma are sometimes able to conjugate with one another (a phenomenon known as selfing),Miyake A. (1981). Cell interaction by gamones in Blepharisma In: Sexual Interactions in Eukaryotic Microbes (O’Day, D.H. editor), pp.

These supplementary reproductives only mature into primary reproductives upon the death of a king or queen, or when the primary reproductives are separated from the colony. Supplementaries have the ability to replace a dead primary reproductive, and there may also be more than a single supplementary within a colony. Some queens have the ability to switch from sexual reproduction to asexual reproduction. Studies show that while termite queens mate with the king to produce colony workers, the queens reproduce their replacements (neotenic queens) parthenogenetically.

It was believed that homothallic forms are intersterile while both bipolar and tetrapolar heterothallic forms are capable of mating. In 1969, Lemke recognized that bipolar heterothallic forms and tetrapolar heterothallic forms also have intersterility as well as homothallic forms. In the study, he defines intersterility as the inability to form a prototrophic heterokaryon through nutritional forcing. The study indicates that all groups are in fact intersterile with each other, meaning that the mating must be carried out within the same group for successful sexual reproduction.

An added process, termed DNA shuffling, mixes and matches pieces of successful variants to produce better results. Such processes mimic the recombination that occurs naturally during sexual reproduction. Advantages of directed evolution are that it requires no prior structural knowledge of a protein, nor is it necessary to be able to predict what effect a given mutation will have. Indeed, the results of directed evolution experiments are often surprising in that desired changes are often caused by mutations that were not expected to have some effect.

Occasionally, three tiny "flowers" consisting of two stamens and a pistil are produced, by which sexual reproduction occurs. Some view this "flower" as a pseudanthium, or reduced inflorescence, with three flowers that are distinctly either female or male and which are derived from the spadix in the Araceae. Evolution of the duckweed inflorescence remains ambiguous due to the considerable evolutionary reduction of these plants from their earlier relatives. The flower of the duckweed genus Wolffia is the smallest known, measuring merely 0.3 mm long.

Due to the slow life cycle and deep-water habitats of black coral, little is known about their life cycle and reproduction. As with other cnidarians, the life cycle of these corals involves both asexual and sexual reproduction. Asexual reproduction (also known as budding), is the first method of reproduction used by a black coral during their lifespan. Once a polyp is anchored, it builds a colony by creating a skeleton, growing new branches and making it thicker, similar to the growth of a tree.

Quasispecies represents the evolution of high-mutation-rate viruses such as HIV and sometimes single genes or molecules within the genomes of other organisms. Quasispecies models have also been proposed by Jose Fontanari and Emmanuel David Tannenbaum to model the evolution of sexual reproduction. Quasispecies was also shown in compositional replicators (based on the Gard model for abiogenesis) and was also suggested to be applicable to describe cell's replication, which amongst other things requires the maintenance and evolution of the internal composition of the parent and bud.

Polyembryony is the phenomenon of two or more embryos developing from a single fertilized egg. Due to the embryos resulting from the same egg, the embryos are identical to one another, but are genetically diverse from the parents. The genetic difference between the offspring and the parents, but the similarity among siblings, are significant distinctions between polyembryony and the process of budding and typical sexual reproduction. Polyembryony can occur in humans, resulting in identical twins, though the process is random and at a low frequency.

In some philodendrons, an additional region of sterile male flowers is found at the very top of the spadix. The fertile female flowers are often not receptive to fertilization when the fertile males are producing pollen, which again prevents self-pollination. The pollen itself is thread- like and appears to project out from the region where the fertile male flowers are located. Sexual reproduction is achieved by means of beetles, with many philodendron species requiring the presence of a specific beetle species to achieve pollination.

Red and Carlene (Cardy), later studied the genetic control of sexual reproduction in the gilled mushroom Schizophyllum commune. Red realized early on there were fungi that differed in aspects of compatibility and attributed these to what he called incompatibility factors A and B, further differentiating α and β in each. Some fungi have two mating types, termed bipolar, and others including some Red worked on, have thousands of mating types due to a more complicated mating type determination system.Raper JR. Sexual hormones in Achlya.

The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals. Choanoflagellates are collared flagellates having a funnel shaped collar of interconnected microvilli at the base of a flagellum. Choanoflagellates are capable of both asexual and sexual reproduction. They have a distinctive cell morphology characterized by an ovoid or spherical cell body 3–10 µm in diameter with a single apical flagellum surrounded by a collar of 30–40 microvilli (see figure).

Her concern is to show how the selection process that occurs in the context of discovery limits what we come to know. Keller argues that the assumption that the atomistic individual is the fundamental unit in nature has led population geneticists to omit sexual reproduction from their models. Though the critique of misplaced individualism is nothing new, the gender dynamics Keller reveals are. According to Keller, geneticists treat reproduction as if individuals reproduce themselves, effectively bypassing the complexities of sexual difference, the contingencies of mating, and fertilization.

Adiantum viridimontanum largely reproduces asexually by branching rather than sexually through spores. While wind-blown spores can result in sexual reproduction for the species, most spores probably fall within a relatively short radius of the plant. In addition, reproduction through spore dispersal requires the spore to land in suitable conditions for generating a gametophyte, typically in bright sunlight on thin serpentine soils. These requirements allow A. viridimontanum to colonize recently disturbed sites on ultramafic outcrops, where bedrock has been exposed and competing plants have been removed.

Obelia dichotoma is a broadly distributed, mainly marine but sometimes freshwater, colonial hydrozoan in the order Leptothecata that forms regular branching stems and a distinctive hydrotheca. O. dichotoma can be found in climates from the arctic to the tropics in protected waters such as marches and creeks but not near open coasts like beaches in depths up to 250m. O. dichotoma uses asexual and sexual reproduction and feeds on mainly zooplankton and fecal pellets. Obelia dichotoma has a complex relationship with the ecosystem and many economic systems.

During the summer months, specifically in Poland Lemna bloom occurs that reduces light attenuation which reduces photosynthesis efficiency of the Chlorella algae, this influences the asexual behavior. Even though during the beginning of the mating season for the Hydra, all the individuals are sexually active, asexual reproduction is the main strategy for reproduction. This behavior of interference of asexual and sexual reproduction allows population growth to continue throughout all conditions. When the Hydra reproduces asexually, buds will be produced that attach to the body wall.

Vegetative apomixis in Poa bulbosa; bulbils form instead of flowers In botany, apomixis was defined by Hans Winkler as replacement of the normal sexual reproduction by asexual reproduction, without fertilization. Its etymology is Greek for "away from" + "mixing". This definition notably does not mention meiosis. Thus "normal asexual reproduction" of plants, such as propagation from cuttings or leaves, has never been considered to be apomixis, but replacement of the seed by a plantlet or replacement of the flower by bulbils were categorized as types of apomixis.

Asplenium resiliens, the blackstem spleenwort or little ebony spleenwort, is a species of fern native to the Western Hemisphere, ranging from the southern United States south to Uruguay, including parts of the Caribbean. Found on limestone substrates, it is named for its distinctive purplish-black stipe and rachis. A triploid, it is incapable of sexual reproduction and produces spores apogamously. First described by Martens and Galeotti in 1842 under the previously used name Asplenium parvulum, the species was given its current, valid name by Kunze in 1844.

When chance produces combinations of good traits, natural selection gives a large advantage to lineages in which these traits become genetically linked. On the other hand, the benefits of good traits are neutralized if they appear along with bad traits. Sexual recombination gives good traits the opportunities to become linked with other good traits, and mathematical models suggest this may be more than enough to offset the disadvantages of sexual reproduction. Other combinations of hypotheses that are inadequate on their own are also being examined.

In 2012, facultative parthenogenesis was reported in wild vertebrates for the first time by US researchers amongst captured pregnant copperhead and cottonmouth female pit-vipers. The Komodo dragon, which normally reproduces sexually, has also been found able to reproduce asexually by parthenogenesis."No sex please, we're lizards", Roger Highfield, Daily Telegraph, 21 December 2006 A case has been documented of a Komodo dragon reproducing via sexual reproduction after a known parthenogenetic event,Virgin birth of dragons, The Hindu, 25 January 2007. Retrieved 3 February 2007.

Kölreuter was the oldest of three sons of an apothecary in Karlsruhe, Germany, and grew up in Sulz. He took an early interest in natural history and made a collection of local insects. At the age of fifteen he went to study medicine at the University of Tübingen under physician and botanist Johann Georg Gmelin who had returned from St. Petersburg. Gmelin had an interest in floral biology and he reprinted a work by Rudolf Jakob Camerarius (who also taught at Tübingen) who was the first to demonstrate sexual reproduction in plants.

260px Acetabularia has three basic parts: its rhizoid, a short set of root-like appendages that contain the nucleus and anchor the cell to fissures in a substrate; its median stalk, which accounts for most of its length; and its apex, where its cap forms. There are usually several whorls of hair-like appendages close to the apex. Acetabularia are among the largest single-celled organisms, having also a remarkably large nucleus. During sexual reproduction, the nucleus undergoes multiple rounds of mitosis, forming many daughter nuclei all within one nuclear membrane.

Drug, toxin, or chemical resistance is a consequence of evolution and is a response to pressures imposed on any living organism. Individual organisms vary in their sensitivity to the drug used and some with greater fitness may be capable of surviving drug treatment. Drug-resistant traits are accordingly inherited by subsequent offspring, resulting in a population that is more drug-resistant. Unless the drug used makes sexual reproduction or cell-division or horizontal gene transfer impossible in the entire target population, resistance to the drug will inevitably follow.

Conditions in the oral cavity are diverse and complex, frequently changing from one extreme to another. Thus, to survive in the oral cavity, S. mutans must tolerate rapidly harsh environmental fluctuations and exposure to various antimicrobial agents to survive. Transformation is a bacterial adaptation involving the transfer of DNA from one bacterium to another through the surrounding medium. Transformation is a primitive form of sexual reproduction. For a bacterium to bind, take up, and recombine exogenous DNA into its chromosome, it must enter a special physiological state termed “competence”.

Blood film from dog infected with Ehrlichia arrowed above within a lymphocyte and Babesia arrowed below in erythrocyte (Giemsa stained) Babesia bovis protozoa are transmitted by R. microplus and cause babesiosis or redwater fever in cattle throughout the tropics and subtropics wherever this boophilid species occurs. The less pathogenic Ba. bigemina is transmitted by R. microplus and R. decoloratorus. Development of Babesia in the tick is complex and includes sexual reproduction. These Babesia are transmitted from adult female boophilid ticks to the next generation, as larvae, by infection of the eggs.

Sexual reproduction in Trichonympha occurs in three distinct phases: gametogenesis, fertilization and meiosis. Gametogenesis occurs when gametes are produced by the division of a haploid cell that has encysted in response to the wood roach host molting. The nucleus and the cytoplasm of the haploid cell divide to produce two unequal gametes. The unequal division is caused by the production of unequal daughter chromosomes, each of which goes to a specific pole. One of the gametes, referred to by Cleveland as the “egg”, develops a ring of fertilization granules at its posterior.

Fungi communicate in the phytobiome through chemical signaling to aid in sexual reproduction, sporulation, cell- to-cell recognition and antibiosis; however, only a fraction of these chemicals have been studied for their function. Mycorrhizal fungi establish symbiotic relationships with plants through the production of Myc factors, or chitooligosaccharides that are recognized by receptors in the plant. Nematode- trapping fungi often utilize fungal signaling molecules to initiate morphogensis towards prey. Other organisms can interfere with fungal signaling, such as plant-produced oxylipins that mimic fungal signaling molecules and can regulate fungal development or reduce virulence.

In this sense there are three types of life cycles that utilize sexual reproduction, differentiated by the location of the organism phase(s). In the diplontic life cycle (with pre-gametic meiosis), of which humans are a part, the organism is diploid, grown from a diploid cell called the zygote. The organism's diploid germ-line stem cells undergo meiosis to create haploid gametes (the spermatozoa for males and ova for females), which fertilize to form the zygote. The diploid zygote undergoes repeated cellular division by mitosis to grow into the organism.

Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a boy. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sex organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when an adult body has been developed.

Dawkins fails to explicitly contrast ancestor organism and descendant organisms against ancestor genes and descendant genes in this chapter. But the first half of the chapter is really about differences between these two models of lineage. While organisms have ancestry graphs and progeny graphs via sexual reproduction, a gene has a single chain of ancestors and a tree of descendants. Given any gene in the body of an organism, we can trace a single chain of ancestor organisms back in time, following the lineage of this one gene, as stated in the coalescent theory.

The second form consists of Coccidinium multiplying rapidly inside the host, however the nucleus does not undergo division until after the death of the host and the encystment of the parasite in its remains. Coccidinium are haplontic, meaning that for the majority of their life cycle they are haploid. Reproduction can occur either asexually or sexually. Sexual reproduction has been clearly observed in 1934 when Chatton and Biecheler witnessed a two-by-two fusion of imperceptibly dissimilar spores from separate organisms of C. mesnilii, resulting in a mobile zygote with two pairs of flagella.

Although parasites are widely considered to be harmful, the eradication of all parasites would not be beneficial. Parasites account for at least half of life's diversity; they perform important ecological roles; and without parasites, organisms might tend to asexual reproduction, diminishing the diversity of traits brought about by sexual reproduction. Parasites provide an opportunity for the transfer of genetic material between species, facilitating evolutionary change. Many parasites require multiple hosts of different species to complete their life cycles and rely on predator–prey or other stable ecological interactions to get from one host to another.

These categories are special cases of a continuum from zero (sympatric) to complete (allopatric) spatial segregation of diverging groups. In multicellular eukaryotic organisms, sympatric speciation is a plausible process that is known to occur, but the frequency with which it occurs is not known. In bacteria, however, the analogous process (defined as "the origin of new bacterial species that occupy definable ecological niches") might be more common because bacteria are less constrained by the homogenizing effects of sexual reproduction and are prone to comparatively dramatic and rapid genetic change through horizontal gene transfer.

Unlike males, therefore, females usually appear physically mature before they are capable of becoming pregnant. Changes in secondary sex characteristics include every change that is not directly related to sexual reproduction. In males, these changes involve appearance of pubic, facial, and body hair, deepening of the voice, roughening of the skin around the upper arms and thighs, and increased development of the sweat glands. In females, secondary sex changes involve elevation of the breasts, widening of the hips, development of pubic and underarm hair, widening of the areolae, and elevation of the nipples.

The genus may be described by properties of its members' gene sequences, or by the shape and form (morphology) of its heads of flowers. When viewed as a whole, the head of flowers looks like a single flower (a pseudanthium). It has a unique kind of pseudanthium, called a cyathium, where each flower in the head is reduced to its barest essential part needed for sexual reproduction. The individual flowers are either male or female, with the male flowers reduced to only the stamen, and the females to the pistil.

Non-human aliens from the other end of the Galaxy visit Earth and kidnap two humans, a man and a woman. They take them up from the surface to their spaceship and question them about human interaction and methods of human reproduction, which is quite different from theirs. The aliens reproduce asexually and the head researcher on humans regards sexual reproduction as an unstable trait that would make humanity too dangerous and worthy of extermination. However, it has trouble convincing the rest of the aliens, who can't imagine two different sexes within the same species.

Sex education is the instruction of issues relating to human sexuality, including emotional relations and responsibilities, human sexual anatomy, sexual activity, sexual reproduction, age of consent, reproductive health, reproductive rights, safe sex, birth control and sexual abstinence. Sex education that covers all of these aspects is known as comprehensive sex education. Common avenues for sex education are parents or caregivers, formal school programs, and public health campaigns. Traditionally, adolescents in many cultures were not given any information on sexual matters, with the discussion of these issues being considered taboo.

It had provided 4,704,000 condoms for safe sex between 2004 and 2007. A 2006 ethnographic study of how antiretroviral therapy interacted with marriage and sexual reproduction in southeast Nigeria determined that many people taking the drugs were doing so secretly. Whilst there were support groups available, there was still a stigma attached to being HIV-positive and noticeable discrimination against people with HIV/AIDS. When Bisi Alimi announced on a national television show in and later on the BBC World Service that he was gay and HIV- positive, he was arrested and beaten up.

This process is significantly promoted in environments with a low food supply. The nematode model species C. elegans and C. briggsae exhibit androdioecy, which is very rare among animals. The single genus Meloidogyne (root-knot nematodes) exhibits a range of reproductive modes, including sexual reproduction, facultative sexuality (in which most, but not all, generations reproduce asexually), and both meiotic and mitotic parthenogenesis. The genus Mesorhabditis exhibits an unusual form of parthenogenesis, in which sperm-producing males copulate with females, but the sperm do not fuse with the ovum.

Eggs leave the vertebrate host in faeces and use various strategies to infect the first intermediate host, in which sexual reproduction does not occur. Digeneans may infect the first intermediate host (usually a snail) by either passive or active means. The eggs of some digeneans, for example, are (passively) eaten by snails (or, rarely, by an annelid worm), in which they proceed to hatch. Alternatively, eggs may hatch in water to release an actively swimming, ciliated larva, the miracidium, which must locate and penetrate the body wall of the snail host.

Once a strain of parasite has overcome these mechanisms, it is able to infect any member of the population. Sexual reproduction mixes up resistance genes through crossing over and the random assortment of gametes in meiosis, meaning the members of a sexual population will all have subtly different combinations of resistance genes. This variation in resistance genes means no one parasite strain is able to sweep through the whole population. New Zealand mudsnails are commonly infected with trematode parasites, which are particularly abundant in shallow water, but scarce in deeper water.

Cryptophyte flagella are inserted parallel to one another, and are covered by bipartite hairs called mastigonemes, formed within the endoplasmic reticulum and transported to the cell surface. Small scales may also be present on the flagella and cell body. The mitochondria have flat cristae, and mitosis is open; sexual reproduction has also been reported. The group have evolved a whole range of light-absorbing pigments, called phycobilins, which are able to absorb wavelengths that's not accessible to other plants or algae, allowing them to live in a variety of different ecological niches.

These findings suggest that the capability for meiosis, and hence sexual reproduction, was present in recent ancestors of T. vaginalis. Twenty-one of the 27 meiosis genes were also found in another parasite Giardia lamblia (also called Giardia intestinalis), indicating that these meiotic genes were present in a common ancestor of T. vaginalis and G. intestinalis. Since these two species are descendants of lineages that are highly divergent among eukaryotes, Malik et al. noted that these meiotic genes were likely present in a common ancestor of all eukaryotes.

Estrogens and progesterone typically regulate motivation to engage in sexual reproduction behaviour for females in mammalian species, though the relationship between hormones and female sexual motivation is not as well understood. In particular, estrogens have been shown to correlate positively with increases in female sexual motivation, and progesterone has been associated with decreases in female sexual motivation. The periovulatory period of the female menstrual cycle is often associated with increased female receptivity and sexual motivation. During this stage in the cycle, estrogens are elevated in the female and progesterone levels are low.

From an evolutionary perspective, increases in estrogens during fertile periods in females may direct sexual motivation toward males with preferential genes (the good genes hypothesis). Following natural or surgically induced menopause, many women experience declines in sexual motivation. Menopause is associated with a rapid decline of estrogen, as well as a steady rate of decline of androgens. The decline of estrogen and androgen levels is believed to account for the lowered levels of sexual reproduction desire and motivation in postmenopausal women, although the direct relationship is not well understood.

These worms are dioecious, with female and male organs having been found in separate individuals. Eggs and immature larvae have been found in tissue samples, indicating an asexual reproductive cycle , and free-living males have been found in soil environments, indicating that sexual reproduction also occurs. The site of entry for the parasite is thought to be through breaks in the skin or through mucous membranes. This nematode is now distributed worldwide, as cases of equine infections have been found in Canada, Florida, the Nordic regions, and Arabian horses alike.

Foliose lichen showing orange apothecia, collected near a California Live Oak (Quercus agrifolia) grove The reproduction of foliose lichen can occur either asexually or sexually. The sexual reproduction requires both a fungal and photosynthetic partner. The photobiont once in symbionce with its fungal partner will not produce recognisable reproductive structures therefore it is up to the fungal partner to continue reproduction for the lichen. In order for lichen reproduction to take place the fungal partner must produce millions of germinating spores which fuse to form a zygote that must then also find a compatible photobiont.

Asexual reproduction covers all those modes of multiplication of plants where normal gamete formation and fertilization does not take place making these distinctly different from normal seed production crops. In the absence of sexual reproduction, the genetic composition of plant material being multiplied remains essentially the same as its source plant. Clones of mother plants can be made with the exact genetic composition of the mother plant. Superior plants are selected and propagated vegetatively; the vegetative propagated offspring are used to develop stable varieties without any deterioration due to segregation of gene combinations.

If the alpha male is removed from the group, a previous subordinate starts exhibiting dominant behavior and egr1 is expressed in hypothalamus neurons that are responsible for producing a neuropeptide linked to sexual reproduction. Overall, the role of transcription factor egr1 in the context of social behavior clearly shows the link between genes and behavior. As a corollary to that described above, given an environmental cue egr1 will induce or suppress the transcription of other genes. Egr1 shows how social experience may trigger changes in the brain's gene networks.

Mutator alleles can also evolve more easily when they only increase mutation rates in nearby DNA sequences, not across the whole genome: this is known as a contingency locus. The evolution of evolvability is less controversial if it occurs via the evolution of sexual reproduction, or via the tendency of variation-generating mechanisms to become more active when an organism is stressed. The yeast prion [PSI+] may also be an example of the evolution of evolvability through evolutionary capacitance. An evolutionary capacitor is a switch that turns genetic variation on and off.

Female carrying an ephippium Cyclic parthenogenesis As most of the other species of the genus Daphnia, D. magna reproduces by cyclical parthenogenesis. This form of reproduction is characterised by the alternating production of asexual offspring (clonal reproduction) and at certain time sexual reproduction through haploid eggs that need to be fertilised. The asexual eggs (up to few dozens per clutch) are diploid and usually develop into females, or in response to adverse environmental stimuli, into males. Asexual eggs hatch in the female brood pouch 1 day after being laid and are released after 3 days.

Ukrainian Phytosociological Centre, Kiev. In sexual reproduction, the species produces small reddish-brown discs known as apothecia containing asci, from which spores are forcibly released into the air (like ballistospores). Based on studies of ascospore germination, it has been suggested that L. pulmonaria spores use some mechanism to inhibit germination—the inhibition is lifted when the spores are grown in a synthetic growth medium containing an adsorbent like bovine serum albumin or α-cyclodextrin. Dispersal by vegetative propagules (via soredia or isidia) has been determined as the predominant mode of reproduction in L. pulmonaria.

In sexual reproduction, mitochondria are normally inherited exclusively from the mother; the mitochondria in mammalian sperm are usually destroyed by the egg cell after fertilization. Also, mitochondria are only in the sperm tail, which is used for propelling the sperm cells and sometimes the tail is lost during fertilization. In 1999 it was reported that paternal sperm mitochondria (containing mtDNA) are marked with ubiquitin to select them for later destruction inside the embryo. Discussed in: Some in vitro fertilization techniques, particularly injecting a sperm into an oocyte, may interfere with this.

50px Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. Stony corals have a great range of reproductive strategies and can reproduce both sexually and asexually. Many species have separate sexes, the whole colony being either male or female, but others are hermaphroditic, with individual polyps having both male and female gonads. Some species brood their eggs but in most species, sexual reproduction results in the production of a free-swimming planula larva that eventually settles on the seabed to undergo metamorphosis into a polyp.

Crocus sativus is unknown in the wild, and its ancestor is unknown. The species Crocus cartwrightianus is the most probable ancestor, but C. thomassi and C. pallasii are still being considered as potential predecessors. Manual vegetative multiplication is necessary to produce offspring for this species as the plant itself is a triploid that is self- incompatible and male sterile, therefore rendering it incapable of sexual reproduction. This inability to reproduce on its own supports the hypothesis that C. sativus is a mutant descending from C. carthwrightianus as a result of selective breeding.

These genes included Spo11, Mre11, Rad50, Rad51, Rad52, Mnd1, Dmc1, Msh, and Mlh. This finding suggests that Acanthamoeba is capable of some form of meiosis and may be able to undergo sexual reproduction. Furthermore, since Acanthamoeba diverged early from the eukaryotic family tree, these results suggest that meiosis was present early in eukaryotic evolution. Owing to its ease and economy of cultivation, the Neff strain of A. castellanii, discovered in a pond in Golden Gate Park in the 1960s, has been effectively used as a classic model organism in the field of cell biology.

Melchior knows about the mechanics of sexual reproduction, but Moritz is woefully ignorant and proposes several hypothetical techniques (such as having brothers and sisters share beds, or sleeping on a firm bed) that might prevent his future children from being as tense and frightened as he is. As an atheist, Melchior blames religion for Moritz's fears. Before departing, Melchior insists Moritz come over to his house for tea, where Melchior will show him diagrams and journals with which he will teach Moritz about life. Moritz leaves hastily, embarrassed.

Puberty is the process of physical changes through which a child's body matures into an adult body capable of sexual reproduction. It is initiated by hormonal signals from the brain to the gonads: the ovaries in a girl, the testes in a boy. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sex organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when an adult body has been developed.

However, several of these protists are now known to be capable of, or to recently have had, the capability for meiosis and hence mating. To cite one example, the common intestinal parasite Giardia intestinalis was once considered to be a descendant of a protist lineage that predated the emergence of meiosis and sex. However, G. intestinalis was recently found to have a core set of genes that function in meiosis and that are widely present among sexual eukaryotes. These results suggested that G. intestinalis is capable of meiosis and thus mating and sexual reproduction.

Pythium dissotocum is a polycyclic oomycete root rot capable of both sexual and asexual reproduction. In its mid-season asexual phase, P. dissotocum disperses by forming a filamentous sporangia, which produce vesicles housing 10-75 motile zoospores. Vesicles open, releasing zoospores which contact host roots, encyst, and produce a germ tube which infects the host root, and begins formation of mycelium. In sexual reproduction, if multiple mating types are present, hyphal antheridium can contact each other and undergo plasmogamy, merging their membranes near the end of growing season.

Darwin's pangenesis theory attempted to explain the process of sexual reproduction, inheritance of traits, and complex developmental phenomena such as cellular regeneration in a unified mechanistic structure. Yongshen Liu wrote that in modern terms, pangenesis deals with issues of "dominance inheritance, graft hybridization, reversion, xenia, telegony, the inheritance of acquired characters, regeneration and many groups of facts pertaining to variation, inheritance and development." Mechanistically, Darwin proposed pangenesis to occur through the transfer of organic particles which he named 'gemmules.' Gemmules, which he also sometimes referred to as },Allaby, Michael.

Mating Cornu aspersum (garden snails) In reproductive biology, a hermaphrodite () is an organism that has complete or partial reproductive organs and produces gametes normally associated with both male and female sexes.Merriam- Webster Dictionary Retrieved 28 June 2011 Many taxonomic groups of animals (mostly invertebrates) do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the "female" or "male". For example, the great majority of tunicates, pulmonate snails, opisthobranch snails, earthworms, and slugs are hermaphrodites.

No sexual reproduction cells or structures have been identified yet, but the asexual reproduction cycle is well understood. Aplanochytrium multiply through spores produced by binary fission and held within the parent wall to form a spherical colorless sporangium. These daughter cells are called aplanospores and are not flagellated. Ten to fifty of these spores are released either due to the complete disintegration of the cell wall or through the production of tears at one or two points in the cell wall, through which the spores can leave the sporangium.

Puberty is the process of physical changes by which a child's body matures into an adult body capable of sexual reproduction to enable fertilization. It is initiated by hormonal signals from the brain to the gonads. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sexual organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when the child has developed an adult body.

Plasmogamy is a stage in the sexual reproduction of fungi, in which the protoplasm of two parent cells (usually from the mycelia) fuses together without the fusion of nuclei, effectively bringing two haploid nuclei close together in the same cell. This state is followed by karyogamy, where the two nuclei fuse together and then undergo meiosis to produce spores. The dikaryotic state that comes after plasmogamy will often persist for many generations before the fungi undergoes karyogamy. In lower fungi however, plasmogamy is usually immediately followed by karyogamy.

It is found in Africa, the Middle East, the Caribbean, Brazil, Venezuela and Suriname. Unlike other flukes (trematodes) in which sexes are not separate (monoecious), schistosomes are unique in that adults are divided into males and females, thus, (dioecious). However, the two adults live in permanent partnership, a condition called in copula; for this, they are considered as hermaphrodites. The life cycle of schistosomes includes two hosts: humans as definitive hosts, where the parasite undergoes sexual reproduction, and snails as intermediate hosts, where a series of asexual reproductive takes place.

Lecidea hassei (Hasse's lecidea lichen) is an endolithic lichen that appears as tiny black, gray rimmed, plate-like or crinkled discs between crystals of rock in California. The main body grows inside solid rock (endolithic), and the crinkled discs above the rock surface are the sexual reproduction structures. It is endemic to California, where it only grows in the lower montane belt, including in deserts and chaparral.The Lichen Flora of Joshua Tree National Park An Annotated Checklist, Kerry Knudsen, Mitzi Harding, Josh Hoines, National Park Service, It occurs in Joshua Tree National Park.

Lichens, Joshua Tree National Park, National Park Service The sexual reproduction structures (apothecia) are black, thinly rimmed (70-100 µm ) with unpigmented fungal tissue surrounding black discs in the middle, and up to 2.2 mm in diameter. They rise out of the rock in a flat to convex disc with a constricted base, giving the appearance of tiny raised plates. It grows in open areas on granite, schist, and other acidic rock. It resembles Lecidea laboriosa but produces schizopeltic acid as a metabolite, instead of 4-O-demethyl planaic acid.

Condensation and resolution of human sister chromatids in early mitosis Chromatids may be sister or non-sister chromatids. A sister chromatid is either one of the two chromatids of the same chromosome joined together by a common centromere. A pair of sister chromatids is called a dyad. Once sister chromatids have separated (during the anaphase of mitosis or the anaphase II of meiosis during sexual reproduction), they are again called chromosomes, each having the same genetic mass as one of the individual chromatids that made up its parent.

Each shrimp is one centimeter in length, but when gathered, the swarms can stretch up to two meters. Using the Artemia’s characteristic of high salinity tolerance, the swarms are formed in water that is too salty to be habitable for fish. Rode and Lievens also hypothesize that the parasitic infection increases the shrimps’ lifespan, time spent at the water surface, and that the castration is to prevent the shrimps from spending time with sexual reproduction. These behaviors would contribute to increasing the chance for the infected Artemia to be consumed by flamingos.

This is due to the randomization of genes passed on to progeny during sexual reproduction. The hybridizer who created a new grex normally chooses to register the grex with a registration authority, thus creating a new grex name, but there is no requirement to do this. Individual plants may be given cultivar names to distinguish them from siblings in their grex. Cultivar names are usually given to superior plants with the expectation of propagating that plant; all genetically identical copies of a plant, regardless of method of propagation (divisions or clones) share a cultivar name.

Fisher's principle is an evolutionary model that explains why the sex ratio of most species that produce offspring through sexual reproduction is approximately 1:1 between males and females. A. W. F. Edwards has remarked that it is "probably the most celebrated argument in evolutionary biology". Fisher's principle was outlined by Ronald Fisher in his 1930 book The Genetical Theory of Natural Selection (but has been incorrectly attributed as original to Fisher). Fisher couched his argument in terms of parental expenditure, and predicted that parental expenditure on both sexes should be equal.

This presence of villose and multiplicative spores is what differentiates C. coronatus from the genus Entomophthora. Though C.coronatus is classified under Zygomycota, it does not produce zygospores and therefore does not undergo sexual reproduction. It has been demonstrated that C. coronatus produces lipolytic, chitinolytic and proteolytic enzymes, especially extracellular proteinases, namely serine proteases which are optimally active at pH 10 and 40 °C. Serine proteases are a diverse group of bacterial, fungal and animal enzymes whose common element is an active site composed of serine, histidine and aspartic acid.

Among the most limiting disadvantages to the evolution of sexual reproduction by natural selection is that an asexual population can grow much more rapidly than a sexual one with each generation. For example, assume that the entire population of some theoretical species has 100 total organisms consisting of two sexes (i.e. males and females), with 50:50 male-to-female representation, and that only the females of this species can bear offspring. If all capable members of this population procreated once, a total of 50 offspring would be produced (the F1 generation).

Lion's mane jellyfish ephyrae form between two medusas Lion's mane jellyfish remain mostly very near the surface, at no more than depth. Their slow pulsations weakly drive them forward, so they depend on ocean currents to travel great distances. The jellyfish are most often spotted during the late summer and autumn, when they have grown to a large size and the currents begin to sweep them to shore. Like other jellyfish, lion's manes are capable of both sexual reproduction in the medusa stage and asexual reproduction in the polyp stage.

These amoeboflagellates also contain a single nucleus, which at this stage in the life cycle is haploid. Under adverse conditions, such as a poor environment, overcrowding or the presence of toxins, these cells can encyst into small, walled cysts that can return to the amoeboflagellate form if conditions improve. The amoeboflagellated stage will undergo sexual reproduction, as two cells fuse to create a diploid cell. This cell will then undergo many rounds of nuclear division without any cellular division, resulting in a rapidly growing, membrane-bound cell with multiple nuclei known as the plasmodium.

Olfactory stimuli are important for sexual reproduction and neuroendocrine function in many species. For instance if a pregnant mouse is exposed to the urine of a 'strange' male during a critical period after coitus then the pregnancy fails (the Bruce effect). Thus, during coitus, a female mouse forms a precise 'olfactory memory' of her partner that persists for several days. Pheromonal cues aid synchronization of oestrus in many species; in women, synchronized menstruation may also arise from pheromonal cues, although the role of pheromones in humans is disputed.

The movement by animals of items involved in plant reproduction is usually a mutualistic association. Pollinators may increase plant reproductive success by reducing pollen waste, increasing dispersal of pollen, and increasing the probability of sexual reproduction at low population density. In return, the pollinator receives nourishment in the form of nectar or pollen. Animals may also disperse the seed or fruit of plants, either by eating it (in which case they receive the benefit of nourishment) or by passive transport, such as seeds sticking to fur or feathers.

Within the cell, the genes are carried in chromosomes, which are packages for carrying the DNA. It is the reshuffling of the chromosomes that results in unique combinations of genes in offspring. Since genes interact with one another during the development of an organism, novel combinations of genes produced by sexual reproduction can increase the genetic variability of the population even without new mutations. The genetic variability of a population can also increase when members of that population interbreed with individuals from a different population causing gene flow between the populations.

The genus Sassafras includes four species, three extant and one extinct. Sassafras plants are endemic to North America and East Asia, with two species in each region that are distinguished by some important characteristics, including the frequency of three-lobed leaves (more frequent in East Asian species) and aspects of their sexual reproduction (North American species are dioecious). Taiwanese sassafras, Taiwan, is treated by some botanists in a distinct genus as Yushunia randaiensis (Hayata) Kamikoti, though this is not supported by recent genetic evidence, which shows Sassafras to be monophyletic.Kamikoti, S. (1933). Ann. Rep.

Chitinozoa may have been immature graptolites. The graptolites are colonial organic walled fossils which also occurred from the Ordovician to the Devonian; only part of their life cycle is known and it is not clear how they reproduced. It has been suggested that the Chitinozoa may represent the pre-sicula stages of graptolites - the period between the colony's sexual reproduction, and the formation of a new colony. This hypothesis appears to be supported by the co- occurrence of graptolite and chitinozoan fossils, whose abundances appear to mirror one another.

During female anthesis, the spadix will project forward at roughly 45° relative to the spathe. Philodendron bipinnatifidum inflorescence The spathe provides a safe breeding area for the beetles. As such, the male beetles are often followed by female beetles with the intent of mating with the males within the spathe. The philodendrons benefit from this symbiotic relationship because the males will eventually leave the spathe covered in pollen and repeat the process at another philodendron, pollinating it in the process and thus providing philodendrons a means of sexual reproduction.

Unfortunately, his original diagnosis was very similar to that of Protomyces, which led others to place species in the wrong genus. In 1877, Nowakowski erected the genus Cladochytrium in the Chytridiales, which led to the transfer of Physoderma to the Chytridiales as well by Schroeter in 1883. Just prior to that (1882), Schroeter added an additional 4 species to the genus and noted, for the first time, epibiotic, ephemeral zoosporangia. He also claimed that sexual reproduction was through the fusion of two cells and resulted in the resting spores.

Hedruris spinigera is a parasite belong to phylum Nematoda, commonly found in the stomach of freshwater fish. The female Hedruris spinigera attaches itself onto the epithelium of the fishes' stomach using a hook at the curved tail. Meanwhile, the male swims freely until it finds a female that has already attached to a host, then the male curls around the body of that female so that sexual reproduction occurs within the host. Most fishes consume Paracorophium excavatum, the intermediate host for Hedruris spinigera; however, the prevalences of Hedruris spinigera are restricted to certain host range.

Human egg cell The egg cell, or ovum (plural ova), is the female reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, "female" gamete and a smaller, "male" one). The term is used when the female gamete is not capable of movement (non-motile). If the male gamete (sperm) is capable of movement, the type of sexual reproduction is also classified as oogamous. When egg and sperm fuse during fertilisation, a diploid cell (the zygote) is formed, which rapidly grows into a new organism.

In 2007, the first case in North Carolina was reported, subtype VGI, which is identical to the isolates found in Australia and California. In 2009, one case was identified in Arkansas. The multiple clonal clusters in the Pacific Northwest likely arose independently of each other as a result of sexual reproduction occurring within the highly sexual VGII population.Billmyre RB, Croll D, Li W, Mieczkowski P, Carter DA, Cuomo CA, Kronstad JW, Heitman J. Highly recombinant VGII Cryptococcus gattii population develops clonal outbreak clusters through both sexual macroevolution and asexual microevolution. MBio.

N. chrosomus increase their food intake during the late winter and spring months before spawning in order to meet the increased energy needs for gamete production and sexual reproduction. Hybridization has been observed between N. baileyi and N. chrosomus in areas where N. chilitious populations have been introduced. There is limited information available pertaining to the current and past management of N. chrosomus. What is known, is that this species was once endemic to parts of northern Alabama and populations have spread further north to Tennessee within recent decades.

Thuret spent a great part of his time, up to 1857, on the Atlantic coast of France, carrying out an intense observation of marine Algae in their natural habitat at all seasons. In conjunction with his friend Edouard Bornet, he became the recognized authority on this important group of plants, of which the two colleagues acquired an unrivalled knowledge. Their work, while remarkable for taxonomic accuracy, was more especially concentrated on the natural history, development and modes of reproduction of the plants investigated. They did much work in the area of sexual reproduction in seaweeds.

The researches on the fecundation of the Fucaceae were published by Thuret in 1853 and 1855; the complicated and difficult question of the sexual reproduction in Floridae was solved by the joint work of Thuret and Bornet (1867). Alongside the important discoveries in this area, the two scientists' researches helped elucidate every group of marine Algae. Thuret's style in expounding his results was hailed as singularly clear and concise; a man of thorough education, he was also noted for expressing his ideas with literary skill. Much of his best work remained unpublished during his life.

Chrysaora fuscescens is capable of both sexual reproduction in the medusa stage and asexual reproduction in the polyp stage. The life cycle of C. fuscescens begins when females catch sperm released by the males to fertilize the eggs she has produced and is holding in her mouth. These fertilized eggs remain attached to her oral arms, and there they grow into flat bean-shaped planula. Once they grow into flower-shaped polyps, they are released into the ocean where they attach themselves to a solid surface and undergo asexual reproduction.

Except for N. infundibula, the species were also found on Punta Cono, 15 April 1990. A strong similarity of the Nieblas—and one other species on the same rock outcrop, Niebla josecuervoi (salazinic acid)—is suggested to be the result of hybridization, and also at another location, Arroyo Sauces, with Niebla flabellata, a species that is characterized by a flattened branch morphology.Niebla homaleoides, World Botanical Associates, retrieved 26 Dec 2014 The prominence of the pycnidia and their potential role in sexual reproduction has to be considered.Robinson, H.1975.

Before dividing into daughter cells, the dividing cells stay attached to each other for approximately 12-24 hours. The doubling time of Coolia is approximately 3-4 days Sexual reproduction occurs as gametes begin to form in the population; this is an irreversible transition. Gametes move around each other rapidly and then align laterally, forming gamete pairs with the girdle and sulcus contacting each other, forming a fertilization bridge. A planozygote is formed when the cells stop moving and the fertilization bridge disappears, allowing the two nuclei to join together.

Fisher's principle outlines why almost all species using sexual reproduction have a sex ratio of 1:1. W. D. Hamilton gave the following basic explanation in his 1967 paper on "Extraordinary sex ratios", given the condition that males and females cost equal amounts to produce: :# Suppose male births are less common than female. :# A newborn male then has better mating prospects than a newborn female, and therefore can expect to have more offspring. :# Therefore, parents genetically disposed to produce males tend to have more than average numbers of grandchildren born to them.

Apomixis occurs in at least 33 families of flowering plants, and has evolved multiple times from sexual relatives. Apomictic species or individual plants often have a hybrid origin, and are usually polyploid. In plants with both apomictic and meiotic embryology, the proportion of the different types can differ at different times of year, and photoperiod can also change the proportion. It appears unlikely that there are any truly completely apomictic plants, as low rates of sexual reproduction have been found in several species that were previously thought to be entirely apomictic.

When the growing season ends, the fungus causes cankers at the base of the plant thereby beginning another necrotrophic stage. Leptosphaeria maculans has both a teleomorph phase (sexual reproduction to generate pseudothecia that release ascospores) and an anamorph phase (asexual reproduction to produce pycnidia that release pycnidiospores). The disease spreads by wind born dispersal of ascospores and rain splash of conidia. In addition, phoma stem canker can also be spread by infected seeds when the fungus infects the seed pods of Brassica napus during the growing season, but this is far less frequent.

The first description of this genus was in 1890 by Kruse who described Haemoproteus columbae in the blood of the pigeon Columba livia. McCallum in 1897 showed that the process of exflagellation was part of sexual reproduction in these parasites and thought it probable that the same process occurred in Plasmodium. The first record of a haemoproteid parasite in a reptile was by Simond in 1901 who gave it the name Haemamoeba metchnikovi. The Sergent brothers in 1906 showed that the ectoparasitic fly Pseudolynchia canariensis was the vector of Haemoproteus columbae.

In addition, sexual reproduction provides the benefit of meiotic recombination between non-sister chromosomes, a process associated with repair of DNA double-strand breaks and other DNA damages that may be induced by stressful conditions. Many taxa with heterogony have within them species that have lost the sexual phase and are now completely asexual. Many other cases of obligate parthenogenesis (or gynogenesis) are found among polyploids and hybrids where the chromosomes cannot pair for meiosis. The production of female offspring by parthenogenesis is referred to as thelytoky (e.g.

So, when the chromosomes go on to meiosis II and separate, some of the daughter cells receive daughter chromosomes with recombined alleles. Due to this genetic recombination, the offspring have a different set of alleles and genes than their parents do. In the diagram, genes B and b are crossed over with each other, making the resulting recombinants after meiosis Ab, AB, ab, and aB. Thomas Hunt Morgan's illustration of crossing over (1916) A double crossing over Chromosomal crossover, or crossing over, is the exchange of genetic material during sexual reproduction between two homologous chromosomes' non-sister chromatids that results in recombinant chromosomes.

He made the important discovery of the effect of the host insect's molting on the sexual reproduction of the host insect's intestinal protozoa. Cleveland collected termites in Panama and Costa Rica with the aid of a grant from the Bache Fund of the National Academy of Sciences. He also collected termites with their symbiotic protozoa (Devescovinidae) in New Zealand and Australia. (Mixotricha paradoxa is an example of a protozoan species in the family Devescovinidae.) Cleveland was in 1952 elected a member of the National Academy of Sciences and in 1955 was president of the Society of Protozoologists.

In cooler areas E. lanigerum spends the winter months as a nymph on the roots of its host plant or in the more sheltered above ground portions of the host such as under bark on the trunk or main branches. Where sexual reproduction occurs they will also overwinter as eggs and this occurs when elms are prevalent with the eggs being laid into crevices in the bark. The eggs hatch out into wingless "stem mothers" who begin to give birth to nymphs by parthenogenesis. Nymph colonies wintering above ground may be wiped out by severe winter weather.

They showed that the characteristics of an organism were carried by inherited genes, which were located on chromosomes in each cell's nucleus. These could be affected by random changes, mutations, and could be shuffled and recombined during sexual reproduction, but were otherwise passed on unchanged from parent to offspring. Beneficial changes could spread through a population by natural selection or, in agriculture, by plant breeding. In contrast, Lamarckism proposes that an organism can somehow pass on characteristics that it has acquired during its lifetime to its offspring, implying that change in the body can affect the genetic material in the germ line.

Aplysia vaccaria is a simultaneous hermaphrodite. Simultaneous hermaphrodites are organisms that have both male and female sex organs that are able to contribute to sexual reproduction at the same time, which is distinct from non-simultaneous hermaphrodites which only have one sex organ present or functional at any one point in time. Being simultaneously hermaphroditic is advantageous because any two individuals are able to reproduce with one another, which facilitates Aplysia vaccaria finding a mate. However, despite having both sex organs functional during reproduction, only one Aplysia vaccaria acts as a sperm donor during the mating encounter.

Resting egg pouch (ephippium) and the juvenile daphnid that just has hatched from it Cladoceran from Daphnia genus giving birth. Magnification is 100X, technique of the illumination: dark field and polarized light Most Daphnia species have a life cycle based on "cyclical parthenogenesis", alternating between parthenogenetic (asexual) reproduction and sexual reproduction. For most of the growth season, females reproduce asexually. They produce a brood of diploid eggs every time they moult; these broods can contain as few as 1–2 eggs in smaller species, such as D. cucullata, but can be over 100 in larger species, such as D. magna.

Such composition may have caused the oceans to be black- and milky-turquoise instead of blue. Despite such adverse conditions, eukaryotes may have evolved around the beginning of the Boring Billion, and adopted several novel adaptations, such as various organelles and possibly sexual reproduction, and diversified into plants, animals, and fungi. Such advances may have been important precursors to the evolution of large, complex life later in the Cambrian explosion. However, prokaryotic cyanobacteria were the dominant lifeforms during this time, and likely supported an energy-poor food-web with a small number of protists at the apex level.

DNA and chromosomes: Chromosomal DNA and Its Packaging in the Chromatin Fiber The full set of hereditary material in an organism (usually the combined DNA sequences of all chromosomes) is called the genome. DNA is most often found in the nucleus of cells, but Ruth Sager helped in the discovery of nonchromosomal genes found outside of the nucleus. In plants, these are often found in the chloroplasts and in other organisms, in the mitochondria. These nonchromosomal genes can still be passed on by either partner in sexual reproduction and they control a variety of hereditary characteristics that replicate and remain active throughout generations.

Mitosis is the normal process in eukaryotes for cell division; duplicating chromosomes and segregating one of the two copies into each of the two daughter cells, in contrast with meiosis. The mitosis theory states that meiosis evolved from mitosis. According to this theory, early eukaryotes evolved mitosis first, became established, and only then did meiosis and sexual reproduction arise. Supporting this idea are observations of some features, such as the meiotic spindles that draw chromosome sets into separate daughter cells upon cell division, as well as processes regulating cell division that employ the same, or similar molecular machinery.

Caenorhabditis elegans The nematode Caenorhabditis elegans and the bacterium Bacillus thuringiensis were only recently established as a model system for studying host–parasite coevolution. Laboratory evolution experiments provided evidence for many of the basic predictions of these coevolutionary interactions, including reciprocal genetic change, and increases in the rate of evolution and genetic diversity. Daphnia magna The crustacean Daphnia and its numerous parasites have become one of the main model systems for studying coevolution. The host can be asexual as well as sexual (induced by changes in the external environment), so sexual reproduction can be stimulated in the laboratory.

In at least one hermaphroditic species, self-fertilization occurs when the eggs and sperm are released together. Internal self-fertilization may occur in some other species. One fish species does not reproduce by sexual reproduction but uses sex to produce offspring; Poecilia formosa is a unisex species that uses a form of parthenogenesis called gynogenesis, where unfertilized eggs develop into embryos that produce female offspring. Poecilia formosa mate with males of other fish species that use internal fertilization, the sperm does not fertilize the eggs but stimulates the growth of the eggs which develops into embryos.

This conflict manifests itself in many traits associated with sexual reproduction. Genes expressed in only one sex are selectively neutral in the other sex; male- and female-linked genes can therefore be acted upon separated by selection and will evolve semi-autonomously. Thus, one sex of a species may evolve to better itself rather than better the species as a whole, sometimes with negative results for the opposite sex: loci will antagonistically coevolve to enhance male reproductive success at females’ expense on the one hand, and to enhance female resistance to male coercion on the other.Trivers, R.L. 1972.

Most species reproduce sexually, but some populations are dominated by hermaphrodites which produce internally fertilised eggs. Reproduction in T. cancriformis varies with latitude, with sexual reproduction dominating in the south of its range, and parthenogenesis dominating in the north. Triops eggs enter a state of extended diapause when dry, and will tolerate temperatures of up to for 16 hours, whereas the adult cannot survive temperatures above for 24 hours or for 2 hours. The diapause also prevents the eggs from hatching too soon after rain; the pool must fill with enough water for the dormancy to be broken.

There are two distinct reproductive strategies within the species Trichoniscus pusillus. Many populations are, like most metazoans, bisexual and reproduce sexually; in other cases, females reproduce parthenogenetically, creating clones of themselves. The sexually reproducing form is diploid while the parthenogenetic form is triploid; since parthenogenesis always produces females, males are always diploid and can only be produced by sexual reproduction. The frequency of males in the population decreases from south to north (a latitudinal cline) and in increasingly open habitats, with no males observed in most of Scotland and Scandinavia, but more than 15% males in the Iberian and Apennine Peninsulas.

P. canariensis is the definitive host (sexual reproduction takes place in the insect vector) for the protozoan Haemoproteus columbae or pigeon malaria and transmits this parasite to Columbiformes. This parasite can be fatal to young Rock Pigeons in extremely infected birds. However, more often, Haemoproteus columbae is quite benign and an experimental study found no difference in experimentally infected birds and those in the surrounding population when followed from nestlings through young adults and monitored for survival. The global distribution of Haemoproteus columbae described in Rock Pigeons may provide evidence for the wide range of Pseudolynchia canariensis.

D. lineata has a tendency to thrive for a time, and then unexpectedly disappear from a locality. D. leucolena on the other hand, living in the same localities and conditions, has stable populations. It is hypothesized that sexual reproduction in the latter gives genetic variability and the flexibility to cope with adverse circumstances, while the asexually-breeding D. lineata, with hardly any genetic variability, succumbs when its limits of tolerance are exceeded. D. leucolena sometimes grows as a fouling organism, and has also been found attached as an epibiont on the carapace of a loggerhead sea turtle (Caretta caretta).

In addition, malnourished children showed poorer scores on intelligence quotient (I.Q.) tests than their supplemented counterparts.Chavez et al. (2000) pp.248-249 Of all the aspects of human existence, sexual reproduction may have the most detailed articulation with malnutrition. In populations subject to MMM, menarche occurs later (15.5 years) than in adequately nourished populations; an early average menopause (40.5 years) makes for a relatively short reproductive period for women in the study area for Chavez et al.Chavez et al. (2000) pp.236, 239 Because of longer postpartum periods of amenorrhea, birth spacing was an average of 27 months, versus 19 months.

Therefore, the Y chromosome and any mutations that arise in it are passed on from father to son in a direct male line of descent. This means the Y chromosome and mtDNA share specific properties. Other chromosomes, autosomes and X chromosomes in women, share their genetic material (called crossing over leading to recombination) during meiosis (a special type of cell division that occurs for the purposes of sexual reproduction). Effectively this means that the genetic material from these chromosomes gets mixed up in every generation, and so any new mutations are passed down randomly from parents to offspring.

However, precise mechanisms by which it passes the blood-brain barrier are still unknown; one recent study in rats suggested an important role of secreted serine proteases. The metalloprotease Mpr1 has been demonstrated to be critical in blood-brain barrier penetration. Meiosis (sexual reproduction), another possible survival factor for intracellular C. neoformans The vast majority of environmental and clinical isolates of C. neoformans are mating type alpha. Filaments of mating type alpha have haploid nuclei ordinarily, but these can undergo a process of diploidization (perhaps by endoduplication or stimulated nuclear fusion) to form diploid cells termed blastospores.

In some charophyte groups, such as the Zygnematophyceae or conjugating green algae, flagella are absent and sexual reproduction does not involve free-swimming flagellate sperm. Flagellate sperm, however, are found in stoneworts (Charales) and Coleochaetales, orders of parenchymatous charophytes that are the closest relatives of the land plants, where flagellate sperm are also present in all except the conifers and flowering plants. Fossil stoneworts of early Devonian age that are similar to those of the present day have been described from the Rhynie chert of Scotland.Somewhat different charophytes have also been collected from the Late Devonian (Famennian) Waterloo Farm lagerstätte of South Africa.

It is also possible to consider the ancestry of individual genes (or groups of genes, haplotypes) instead of an organism as a whole. Coalescent theory describes a stochastic model of how the ancestry of such genetic markers maps to the history of a population. Unlike organisms, a gene is passed down from a generation of organisms to the next generation either as perfect replicas of itself or as slightly mutated descendant genes. While organisms have ancestry graphs and progeny graphs via sexual reproduction, a gene has a single chain of ancestors and a tree of descendants.

It rather reflects the presence of a single individual with high reproductive success in the past, whose genetic contribution has become pervasive throughout the population over time. It is also incorrect to assume that the MRCA passed all, or indeed any, genetic information to every living person. Through sexual reproduction, an ancestor passes half of his or her genes to each descendant in the next generation; after more than 32 generations the contribution of a single ancestor would be on the order of 2−32, a number proportional to less than a single basepair within the human genome.

The Ciber Logo The Centre for Integrative Bee Research (CIBER) is located on the Crawley campus at the University of Western Australia in Perth. CIBER conducts basic scientific research into honeybee reproduction, immunity and ecology and aligns its work with the needs of industrial and governmental partners. CIBER is specifically dedicated to facilitate interdisciplinary research and offers opportunities for scientists to perform collaborative research on honeybees using methods and approaches from systems biology and evolutionary ecology. The ultimate goal is to better understand how individual molecules and their interplay are responsible for complex biological process such as sexual reproduction or immunity.

The shapes of these virus particles range from simple helical and icosahedral forms to more complex structures. Most virus species have virions too small to be seen with an optical microscope, as they are one-hundredth the size of most bacteria. The origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity in a way analogous to sexual reproduction.

Initially, it was thought that the fungus suppresses sexual reproduction in Trebouxia to inhibit the formation of novel genotypes that could be less suitable for symbiosis. However, it has recently been proposed that Trebouxia are more likely to reproduce sexually in lichen thallus. Furthermore, gametes from different Trebouxia species can escape the thallus and fuse to form hybrids or divide asexually to form micro colonies that can later be lichenized by fungi spores. Additional evidence of viable fungi spores and Trebouxia spores in fecal matter of lichen eating mites provides insight into short and long distance dispersal modes.

Physical sex characteristics include primary sex characteristics and secondary sex characteristics. A primary sexual characteristic, as narrowly defined, is any anatomical part of the body involved in sexual reproduction and constituting the reproductive system in a complex organism, especially the external sex organs; the external sex organs are also commonly referred to as the genitalia or genitals. Secondary sex characteristics are features that appear at sexual maturity in animals and during puberty in humans, especially the sexually dimorphic phenotypic traits that distinguish the sexes of a species, but that, unlike the sex organs, are not directly part of the reproductive system.

Isogamy is a form of sexual reproduction that involves gametes of similar morphology (similar shape and size), differing in general only in allele expression in one or more mating-type regions. Because both gametes look alike, they cannot be classified as "male" or "female". Instead, organisms undergoing isogamy are said to have different mating types, most commonly noted as "+" and "−" strains, although in some species of Basidiomycota there are more than two mating types (designated by numbers or letters). In all cases, fertilization occurs when gametes of two different mating types fuse to form a zygote.

Many interconnected hyphae form a thallus usually referred to as the mycelium, which—when visible to the naked eye (macroscopic)—is commonly called mold. During sexual reproduction, many Ascomycota typically produce large numbers of asci. The ascus is often contained in a multicellular, occasionally readily visible fruiting structure, the ascocarp (also called an ascoma). Ascocarps come in a very large variety of shapes: cup-shaped, club-shaped, potato-like, spongy, seed-like, oozing and pimple-like, coral-like, nit-like, golf-ball-shaped, perforated tennis ball- like, cushion-shaped, plated and feathered in miniature (Laboulbeniales), microscopic classic Greek shield-shaped, stalked or sessile.

Mature zoospores can be induced to germinate by treatment with 0.25% KMnO4 for 20 min and incubation under light during germination. Although sporangia and zoospores may survive in soil for short periods, chlamydospores are the main survival structure for P. palmivora in nature. Zoospores are capable of long-term survival but do not play a significant role in the disease cycle because sexual reproduction in P. palmivora requires the presence of opposite mating types, and the chance for this to occur in nature is very low. During rainy periods, chlamydospores in soil may germinate in water to produce sporangia and release zoospores.

It has been found that where plants have been damaged mechanically, such as by the propellers of boats, the cut ends of rhizomes are unable to grow and holes may develop in the turtle grass meadow. Turtle grass can also sexually reproduce through the production of underwater flowers and hydrophily. Turtle grass is dioecious, which means that there are separate male and female plants, each which produce an imperfect flower containing only one sex. Sexual reproduction takes place from April to July depending on location, though flowering has been observed during warm winters in Tampa Bay, Florida.

The evolution of sexual reproduction may be a primordial and fundamental characteristic of eukaryotes. Based on a phylogenetic analysis, Dacks and Roger proposed that facultative sex was present in the common ancestor of all eukaryotes. A core set of genes that function in meiosis is present in both Trichomonas vaginalis and Giardia intestinalis, two organisms previously thought to be asexual. Since these two species are descendants of lineages that diverged early from the eukaryotic evolutionary tree, it was inferred that core meiotic genes, and hence sex, were likely present in a common ancestor of all eukaryotes.

The life cycle of M. amygdalinae is macrocyclic, or has all spore states in its life cycle, which is important to know when trying to perform any disease management. In the spring it undergoes sexual reproduction and the teliospores germinate after overwintering, then produce basidia. The basidia then release basidiospores that travel through the wind to infect the host plant. The host is infected by the haploid basidiospores that form spermagonia. “After dikaryotization by transfer of spermatia to the receiving structures of compatible mating types, aecia are formed. From these, aecidiospores are dispersed, which, after germination, form uredia on infected host tissue”.

The named, 'human,' Cylon models initially refer to the five with reverence; it soon become clear that they are programmed to avoid thinking directly about the five, as their identities are hidden, even from Cylons. Circumventing this programming kills a model three shortly after her revelation, and a model one, Cavil, puts her consciousness into cold storage after resurrection to prevent her from discussing the discovery ("Rapture"). They were the original humanoid Cylons, born 2,000 years before the series, on Earth, as part of the Thirteenth Tribe. ("Sometimes a Great Notion") They were born to Cylon parents through sexual reproduction, rather than built.

In the latter, the sperm and egg cells can come from a different flower on the same plant. While the latter method does blur the lines between autogamous self-fertilization and normal sexual reproduction, it is still considered autogamous self-fertilization. Self-pollination can lead to inbreeding depression due to expression of deleterious recessive mutations. Meiosis followed by self-pollination results in little genetic variation, raising the question of how meiosis in self-pollinating plants is adaptively maintained over an extended period in preference to a less complicated and less costly asexual ameiotic process for producing progeny.

The most widely used embryo rescue procedure is referred to as embryo culture, and involves excising plant embryos and placing them onto media culture. Embryo rescue is most often used to create interspecific and intergeneric crosses that would normally produce seeds which are aborted. Interspecific incompatibility in plants can occur for many reasons, but most often embryo abortion occurs In plant breeding, wide hybridization crosses can result in small shrunken seeds which indicate that fertilization has occurred, however the seed fails to develop. Many times, remote hybridizations will fail to undergo normal sexual reproduction, thus embryo rescue can assist in circumventing this problem.

Commonly hailed as one of the most significant evolutionary biologists of his time, Fisher was also a talented geneticist. His book The Genetical Theory of Natural Selection, published in 1930, over 20 years before the double-helix shape of DNA was discovered, was the first attempt to explain Darwin's theories within the foundation of genetics. Chapter 6 of this book is titled "Sexual Reproduction and Sexual Selection" and includes a genetic interpretation of Darwin's initial idea of sex-limited genes. After these groundbreaking works, papers continue to be published further exploring the causes, mechanisms, evolutionary advantages, and more of sex-limited genes.

Although brewers' yeast (Saccharomyces), fission yeast (Schizosaccharomyces), and Aspergillus flavus have no detectable DNA methylation, the model filamentous fungus Neurospora crassa has a well-characterized methylation system. Several genes control methylation in Neurospora and mutation of the DNA methyl transferase, dim-2, eliminates all DNA methylation but does not affect growth or sexual reproduction. While the Neurospora genome has very little repeated DNA, half of the methylation occurs in repeated DNA including transposon relics and centromeric DNA. The ability to evaluate other important phenomena in a DNA methylase-deficient genetic background makes Neurospora an important system in which to study DNA methylation.

In bacteria, these stresses induce an altered physiologic state, termed competence, that allows active take-up of DNA from a donor bacterium and the integration of this DNA into the recipient genome (see Natural competence) allowing recombinational repair of the recipients' damaged DNA. If environmental stresses leading to DNA damage were a persistent challenge to the survival of early microorganisms, then selection would likely have been continuous through the prokaryote to eukaryote transition, and adaptative adjustments would have followed a course in which bacterial transformation or archaeal DNA transfer naturally gave rise to sexual reproduction in eukaryotes.

For these transformations to lead to the eukaryotic cell cycle, the VE hypothesis specifies a pox-like virus as the lysogenic virus. A pox-like virus is a likely ancestor because of its fundamental similarities with eukaryotic nuclei. These include a double stranded DNA genome, a linear chromosome with short telomeric repeats, a complex membrane bound capsid, the ability to produce capped mRNA, and the ability to export the capped mRNA across the viral membrane into the cytoplasm. The presence of a lysogenic pox-like virus ancestor explains the development of meiotic division, an essential component of sexual reproduction.

The issue of the evolution of sexual reproduction features in the writings of Aristotle, and modern philosophical- scientific thinking on the problem dates from at least Erasmus Darwin (1731–1802) in the 18th century. August Weismann picked up the thread in 1889, arguing that sex serves to generate genetic variation, as detailed in the majority of the explanations below. On the other hand, Charles Darwin (1809–1882) concluded that the effect of hybrid vigor (complementation) "is amply sufficient to account for the ... genesis of the two sexes". This is consistent with the repair and complementation hypothesis, described below.

Sexual reproduction implies that chromosomes and alleles segregate and recombine in every generation, but not all genes are transmitted together to the offspring. There is a chance of spreading mutants that cause unfair transmission at the expense of their non- mutant colleagues. These mutations are referred to as "selfish" because they promote their own spread at the cost of alternative alleles or of the host organism; they include nuclear meiotic drivers and selfish cytoplasmic genes. Meiotic drivers are genes that distort meiosis to produce gametes containing themselves more than the 50% of the time expected by chance.

Chlamydomonas has been used to study different aspects of evolutionary biology and ecology. It is an organism of choice for many selection experiments because (1) it has a short generation time, (2) it is both a heterotroph and a facultative autotroph, (3) it can reproduce both sexually and asexually, and (4) there is a wealth of genetic information already available. Some examples (nonexhaustive) of evolutionary work done with Chlamydomonas include the evolution of sexual reproduction, the fitness effect of mutations,De Visser et al. 1996 The effect of sex and deleterious mutations on fitness in Chlamydomonas. Proc.

Anatomy of the flower. A diagram illustrating flower development in Arabidopsis. Flower development is the process by which angiosperms produce a pattern of gene expression in meristems that leads to the appearance of an organ oriented towards sexual reproduction, the flower. There are three physiological developments that must occur in order for this to take place: firstly, the plant must pass from sexual immaturity into a sexually mature state (i.e. a transition towards flowering); secondly, the transformation of the apical meristem’s function from a vegetative meristem into a floral meristem or inflorescence; and finally the growth of the flower’s individual organs.

The saffron crocus, unknown in the wild, probably descends from Crocus cartwrightianus. It is a triploid that is "self-incompatible" and male sterile; it undergoes aberrant meiosis and is hence incapable of independent sexual reproduction—all propagation is by vegetative multiplication via manual "divide-and-set" of a starter clone or by interspecific hybridisation. Crocus sativus thrives in the Mediterranean maquis, an ecotype superficially resembling the North American chaparral, and similar climates where hot and dry summer breezes sweep semi-arid lands. It can nonetheless survive cold winters, tolerating frosts as low as and short periods of snow cover.

This sex-specific selection between sexes over time also lead to the development of secondary sex characteristics, which assist males and females in reproductive success. In most species, both sexes choose mates based on the available phenotypes of potential mates. These phenotypes are species specific, resulting in varying strategies for successful sexual reproduction. For example, large males are sexually selected for in elephant seals for their large size helps the male fight off other males, but small males are sexually selected for in spiders for they can mate with the female more quickly while avoiding sexual cannibalism.

It does not matter how fit and fertile a phenotype is, it will eventually be destroyed and will never be duplicated. Since 1954, it has been known that DNA is the main physical substrate to genetic information, and it is capable of high-fidelity replication through many generations. So, a particular gene coded in a nucleobase sequence of a lineage of replicated DNA molecules can have a high permanence and a low rate of endogenous change. In normal sexual reproduction, an entire genome is the unique combination of father's and mother's chromosomes produced at the moment of fertilization.

Colonies are either male or female and sexual reproduction occurs in Mediterranean populations. With a period of five or six months, the length of gametogenesis is shorter than for any other littoral octocorals. Larvae have been observed in the gastric cavity of females in May and in the open water in June, being ready to settle in early summer, a time at which the host corals are most vulnerable because of their own breeding activities. In the Atlantic, reproduction is mainly by parthenogenesis, with embryos being brooded inside the gastric cavity of their parent, to be liberated as juveniles with limited dispersal ability.

It is probable that sexual reproduction in this species is similar to other members of the genus. However a much more common means of dispersal involves asexual reproduction, with fragments of the plant breaking off and re-establishing themselves elsewhere. In its native surroundings, this seaweed is kept in check by herbivorous fish but in Florida, few if any fish feed on it and it can flourish on off-shore reefs, reducing biodiversity. It is intolerant of bright light, growing best in shaded positions, being mostly found in the depth range where there is less light than at the surface.

The daughter cell produced during the budding process is generally smaller than the mother cell. Some yeasts, including Schizosaccharomyces pombe, reproduce by fission instead of budding, and thereby creating two identically sized daughter cells. In general, under high-stress conditions such as nutrient starvation, haploid cells will die; under the same conditions, however, diploid cells can undergo sporulation, entering sexual reproduction (meiosis) and producing a variety of haploid spores, which can go on to mate (conjugate), reforming the diploid. The haploid fission yeast Schizosaccharomyces pombe is a facultative sexual microorganism that can undergo mating when nutrients are limiting.

In the classical Galton-Watson process described above, only men are considered, effectively modeling reproduction as asexual. A model more closely following actual sexual reproduction is the so-called "bisexual Galton-Watson process", where only couples reproduce. (Bisexual in this context refers to the number of sexes involved, not sexual orientation.) In this process, each child is supposed as male or female, independently of each other, with a specified probability, and a so-called "mating function" determines how many couples will form in a given generation. As before, reproduction of different couples are considered to be independent of each other.

Biota of North America Program, 2014 county distribution map, Agnorhiza reticulataCalflora taxon report, University of California @ Berkeley, Wyethia reticulata E. Greene El Dorado County mule ears, El Dorado mule ears, Eldorado wyethia The genetic diversity of the populations is probably low because they are often clonal, spreading via vegetative reproduction with rhizomes rather than sexual reproduction by seed. Some populations are also threatened by development of their habitat.Ayres, D. R. and F. J. Ryan. (1999). Genetic diversity and structure of the narrow endemic Wyethia reticulata and its congener W. bolanderi (Asteraceae) using RAPD and allozyme techniques.

Aquilonastra burtoni is a benthic species which occurs in shallow waters between 0 and 10m in depth where is common in the lower the lower shore below the low tide line under rock slabs and boulders. It is uncommon in the gravel tails and gravelly hydraulic banks, its preferred food is seems to be the rich shade-loving animals that live underneath blacks and slabs, including sponges such as Spirastrella spp and Timea spp. or Ascidiacea, for example Trididemnum or Eudistoma. In sexual reproduction the eggs and sperm are broadcast and the larvae are planktonic lecithotrophs, i.e.

The gap is narrowing to some extent in some developed countries, possibly due to increased smoking among women and declining rates of cardiovascular disease among men. The World Health Organization writes that it is "important to note that the extra years of life for women are not always lived in good health." Woman nursing her infant Until the maturation of their reproductive capabilities, the pre-pubertal physical differences between boys and girls consists of the differences in their genitalia. Puberty is the process of physical changes by which a child's body matures into an adult body capable of sexual reproduction to enable fertilization.

Lepidurus glacialias, very similar in body shape to Lepidurus apus Lepidurus apus, commonly known as a tadpole shrimp, is a notostracan in the family Triopsidae, one of a lineage of shrimp-like crustaceans that have had a similar form since the Triassic period and are considered living fossils. This species is cosmopolitan, inhabiting temporary freshwater ponds over much of the world, and the most widespread of the tadpole shrimps. Like other notostracans, L. apus has a broad carapace, long segmented abdomen, and large numbers of paddle-like legs. It reproduces by a mixture of sexual reproduction and self-fertilisation of females.

The Red Queen hypothesis describes coevolutionary 'arms races' between antagonistic species (predators and prey, parasites and hosts, competitors with overlapping niches), emphasizing competition between species and populations rather than within them. Under Red Queen dynamics, a species must adapt to shifting selection pressures of the ever-changing biota which constitute its environment or face extinction. Experiments in Red Queen environments on real and simulated populations have offered strong support for the maintenance of sexual reproduction despite the two-fold cost of sex. Fluctuating selection may also play an important role in host-parasite coevolutionary relationships, specifically in the maintenance of sex.

The defining characteristics of sexual reproduction in eukaryotes are meiosis and fertilization. There is much genetic recombination in this kind of reproduction, in which offspring receive 50% of their genes from each parent, in contrast with asexual reproduction, in which there is no recombination. Bacteria also exchange DNA by bacterial conjugation, the benefits of which include resistance to antibiotics and other toxins, and the ability to utilize new metabolites. However, conjugation is not a means of reproduction, and is not limited to members of the same species – there are cases where bacteria transfer DNA to plants and animals.

These features would also have provided opportunities for other organisms to diversify, by creating more varied environments than flat microbial mats could. Multicellularity with differentiated cells is beneficial to the organism as a whole but disadvantageous from the point of view of individual cells, most of which lose the opportunity to reproduce themselves. In an asexual multicellular organism, rogue cells which retain the ability to reproduce may take over and reduce the organism to a mass of undifferentiated cells. Sexual reproduction eliminates such rogue cells from the next generation and therefore appears to be a prerequisite for complex multicellularity.

Like all ciliates, O. trifallax has two different types of nuclei: macronuclei, which are the site of transcription and gene expression, and micronuclei, which are only active during sexual reproduction but are otherwise transcriptionally inactive. Macronuclei are formed by the differentiation of micronuclei, which usually involves some degree of RNA-mediated DNA editing. O. trifallax is the first species sequenced with an unusually high degree of fragmentation in its macronuclear genome. Up to 96% of the micronuclear genome is eliminated during the differentiation into a macronucleus; in comparison, in other ciliates like Paramecium only about 30% is eliminated.

Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Two genetic markers that are physically near to each other are unlikely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be more linked than markers that are far apart. In other words, the nearer two genes are on a chromosome, the lower the chance of recombination between them, and the more likely they are to be inherited together. Markers on different chromosomes are perfectly unlinked.

The switch between sexuality and parthenogenesis in such species may be triggered by the season (aphid, some gall wasps), or by a lack of males or by conditions that favour rapid population growth (rotifers and cladocerans like Daphnia). In these species asexual reproduction occurs either in summer (aphids) or as long as conditions are favourable. This is because in asexual reproduction a successful genotype can spread quickly without being modified by sex or wasting resources on male offspring who won't give birth. In times of stress, offspring produced by sexual reproduction may be fitter as they have new, possibly beneficial gene combinations.

As a consequence, the males will only have fathers and the queens only mothers, while the sterile workers are the only ones with both parents of both genders. These ants get both the benefits of both asexual and sexual reproduction—the daughters who can reproduce (the queens) have all of the mother's genes, while the sterile workers whose physical strength and disease resistance are important are produced sexually. Other examples of insect parthenogenesis can be found in gall-forming aphids (e.g., Pemphigus betae), where females reproduce parthenogenetically during the gall-forming phase of their life cycle and in grass thrips.

This occurs as sexual reproduction involves the fusion of two haploid gametes (the egg and sperm) to produce a zygote and a new organism, in which every cell has two sets of chromosomes (diploid). During gametogenesis the normal complement of 46 chromosomes needs to be halved to 23 to ensure that the resulting haploid gamete can join with another haploid gamete to produce a diploid organism. In independent assortment, the chromosomes that result are randomly sorted from all possible maternal and paternal chromosomes. Because zygotes end up with a mix instead of a pre-defined "set" from either parent, chromosomes are therefore considered assorted independently.

Most animals and some plants have paired chromosomes, and are described as diploid. They have two versions of each chromosome, one contributed by the mother's ovum, and the other by the father's sperm, known as gametes, described as haploid, and created through meiosis. These gametes then fuse during fertilization during sexual reproduction, into a new single cell zygote, which divides multiple times, resulting in a new organism with the same number of pairs of chromosomes in each (non-gamete) cell as its parents. Each chromosome of a matching (homologous) pair is structurally similar to the other, and has a very similar DNA sequence (loci, singular locus).

In Growing Artificial Societies: Social Science From the Bottom Up, Epstein and Axtell developed the first large-scale agent-based computational model, the Sugarscape, to explore the role of social phenomenon such as seasonal migrations, pollution, sexual reproduction, combat, and transmission of disease and even culture. He has published in the modeling area, including recent articles on the dynamics of civil violence,Epstein, Joshua M. Modeling civil violence: An agent-based computational approach PNAS vol. 99, May 14, 2002, p. 7243-7250. the demography of the AnasaziAxtell, R. L., Epstein, J. M., Dean, J. S., Gumerman, G. J., Swedlund, A. C., Harburger, J., ... & Parker, M. (2002).

In the Spring, April in Great Britain, the colonies begin to produce young which infest the host tree and if there are no above ground colonies they move up the tree until almost the whole tree is covered in aphid colonies, which prefer to be sited at the axils of leaves on terminal shoots. Where the population levels are high almost every leaf on the tree will have a colony at its base. The third generation of young produced grow into winged adult females which are capable of sexual reproduction. each female producing a single egg, but these can only develop on the American elm Ulmus americana.

After successful infection, the leaf blade is colonized and sporulation will occur through the stomata. One lesion produces 4–6 spore crops over a 3–5 month period releasing 300–400,000 spores. While the predominant hypothesis is that H. vastatrix is heteroecious, completing its life cycle on an alternate host plant which has not yet been found, an alternative hypothesis is that H. vastatrix actually represents an early-diverging autoecious rust, in which the teliospores are non-functional and vestigial, and the sexual life cycle is completed by the urediniospores. Hidden meiosis and sexual reproduction (cryptosexuality) has been found within the generally asexual urediniospores.

The second species discovered, Sappinia diploidea was originally named Amoeba diploidea, and was first found in 1908 by Max Hartmann and Kurt Nägler. It was isolated from the intestinal material of a lizard; however, it was not thought to be parasitic, as it was not found in 20 other lizards sampled, and a very similar strain was isolated from soil. It was named “diploidea” because the organism was only ever seen in the diploid stage. Nägler stated that there is no true haploid stage; however, further studies have not been able to come to this conclusion, as the nuclei become difficult to discern during sexual reproduction.

Sexual reproduction has not been observed in P. capsulatus but its mode of asexual reproduction is quite distinctive. The cell splits into two daughter cells while remaining inside the original cell wall, one daughter cell then begins to enlarge, while the other is pushed out of a small hole in the parental cell wall. The larger cell remains in the original cell wall while the other migrates to the edge of the capsule which surrounds them both. Before leaving the parental capsule this daughter has synthesised its own firm cell wall after which it leaves the parental capsule and begins to produce its own capsule.

Zoospores of parasitic chytrids use light and chemical cues to locate hosts. Zoospores of Rhizophydium littoreum, a parasite of marine green algae, are positively phototactic toward blue light, a mechanism that might assure that zoospores swim to the photic zone where its host resides. Zoospores of both R. littoreum and B. dendrobatidis exhibit chemotaxis to specific sugars, proteins and amino acids, also a mechanism by which zoospores might detect signals to potential hosts. Sexual reproduction is more rarely reported and occurs when two adjacent sporangia function as gametangia with one transferring all of its cytoplasmic contents into the other, resulting in the development of a thick-walled, lipid-laden resting spore.

Females can produce full clones of themselves through a modification of the normal meiosis process used to produce haploid egg cells for sexual reproduction. The female's germ cells undergo a process of premeiotic genome doubling, or endoreduplication, so that two consecutive division cycles in the process of meiosis result in a diploid, rather than haploid, genome. Whereas homologous chromosomes pair and separate during meiosis I in sexual species, identical duplicate sister chromosomes, produced through premeiotic replication, pair and separate during meiosis I in true parthenotes. Pairing of identical sister chromosomes, in comparison to the alternative of pairing homologous chromosomes, maintains heterozygosity in obligate parthenotes.

The evidence of both spatial structuring and invasion has been shown for this disease. Population genetic analyses indicate a strong regional heterogeneity in levels of recombination, with clear signatures of recombination in the Himalayan and near-Himalayan regions and a predominant clonal population structure in other regions. The existence of a high genotypic diversity, recombinant population structure, high sexual reproduction ability, and the abundance of alternate host (Berberis spp.) in the Himalayan and neighboring regions suggest the region as plausible Pst center of origin or at least the most closer to its centre of origin. However, further exploration may be useful from Central Asia to East Asian regions.

A sperm fertilizing an egg in sexual reproduction is one stage of reproductive success Reproductive success is defined as an individual's production of offspring per breeding event or lifetime. This is not limited by the number of offspring produced by one individual, but also the reproductive success of these offspring themselves. Reproductive success is different from fitness in that individual success is not necessarily a determinant for adaptive strength of a genotype since the effects of chance and the environment have no influence on those specific genes. Reproductive success turns into a part of fitness when the offspring are actually recruited into the breeding population.

The genome of C. albicans is highly dynamic, contributed by the different CUG translation, and this variability has been used advantageously for molecular epidemiological studies and population studies in this species. The genome sequence has allowed for identifying the presence of a parasexual cycle (no detected meiotic division) in C. albicans. This study of the evolution of sexual reproduction in six Candida species found recent losses in components of the major meiotic crossover-formation pathway, but retention of a minor pathway. The authors suggested that if Candida species undergo meiosis it is with reduced machinery, or different machinery, and indicated that unrecognized meiotic cycles may exist in many species.

Author Lance Parkin, who devised the character of Miranda, has hinted that her real father is a future incarnation of the Doctor which, if so, would make Zezanne the Doctor's biological granddaughter as well. The Virgin New Adventures novel Lungbarrow presents an alternative take on the Doctor's origins, suggesting that Time Lords are "loomed" in large batches of "cousins" and not produced via sexual reproduction. Lungbarrow portrays the Doctor as being one of 45 cousins grown from his house's genetic loom as an adult. By contrast, the TV programme has shown Time Lords as children, and stated that Time Lords can have sexual relationships.

Diagram of a human sperm cell Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, "female" reproductive cell and a smaller, "male" one). Animals produce motile sperm with a tail known as a flagellum, which are known as spermatozoa, while some red algae and fungi produce non-motile sperm cells, known as spermatia. Flowering plants contain non-motile sperm inside pollen, while some more basal plants like ferns and some gymnosperms have motile sperm. Sperm cells form during the process known as spermatogenesis, which in amniotes (reptiles and mammals) takes place in the seminiferous tubules of the testes.

Such time to most recent common ancestor (TMRCA) estimates can be given based on DNA test results and established mutation rates as practiced in genetic genealogy, or by reference to a non-genetic, mathematical model or computer simulation. In organisms using sexual reproduction, the matrilinear MRCA and patrilinear MRCA are the MRCAs of a given population considering only matrilineal and patrilineal descent, respectively. The MRCA of a population by definition cannot be older than either its matrilinear or its patrilinear MRCA. In the case of Homo sapiens, the matrilinear and patrilinear MRCA are also known as "Mitochondrial Eve" (mt-MRCA) and "Y-chromosomal Adam" (Y-MRCA) respectively.

His data are assembled from his own observations, statements given by people with specialised knowledge such as beekeepers and fishermen, and less accurate accounts provided by travellers from overseas. His observations on catfish, electric fish (Torpedo) and angler fish are detailed, as is his writing on cephalopods including the octopus, cuttlefish and paper nautilus. His claim that the octopus had a hectocotyl arm which was perhaps used in sexual reproduction was widely disbelieved, until its rediscovery in the 19th century. He separated the aquatic mammals from fish, and knew that sharks and rays were part of the group he called Selachē (roughly, the modern zoologist's selachians).

Three thousand years before the story starts, Lysos founds a human colony on the isolated planet of Stratos in an effort to radically re- engineer human life into a happier, more pastoral form. She developed a strain of human beings that conceives clones in winter (always female), while those conceived in summer (variants or "vars") obtain their genes through sexual reproduction just in case biological adaptation becomes necessary. Further, males and females have opposed seasons of sexual receptivity: men in summer and women in winter. This scheme is said to be stable over evolutionary time because women gain an advantage from self-cloning, while men only reproduce in summer.

As seen on a few occasions, unlike most monsters, shapeshifters are not created through a person being turned but are in fact made through sexual reproduction with one shapeshifter parent and one regular human parent. Most shapeshifters shed their skin when changing appearances, but in season 9 a few were able to change form without shedding skin similar to the Alpha Shapeshifter, the very first shapeshifter. They are vulnerable to silver which burns them on contact and kills them when they are stabbed or shot through the heart with it. On camera, their eyes give off a glow referred to as a retinal flare which helps to identify them.

Animals fixed in place must rely on the surrounding medium to bring food at least close enough to grab, and this occurs in the three-dimensional water environment, but with much less abundance in the atmosphere. All of the marine and aquatic invertebrates whose lives are spent fixed to the bottom (more or less; anemones are capable of getting up and moving to a new location if conditions warrant) produce dispersal units. These may be specialized "buds", or motile sexual reproduction products, or even a sort of alteration of generations as in certain cnidaria. Corals provide a good example of how sedentary species achieve dispersion.

Illustration of chromosome crossover during genetic recombination In evolutionary genetics, Muller's ratchet (named after Hermann Joseph Muller, by analogy with a ratchet effect) is a process in which absence of recombination, especially in an asexual population, results in accumulation of deleterious mutations (harmful mutations) in an irreversible manner. (Muller's original 1932 paper) (original paper as cited by, e.g.: ; ) This happens due to the fact that in the absence of recombination, offspring at least bear the same mutational load as their parents (assuming reverse mutations are rare). Muller proposed this mechanism as one reason why sexual reproduction may be favored over asexual reproduction, as sexual organisms benefit from recombination.

Human male XY chromosomes after G-banding A sex chromosome, (also referred to as an allosome, heterotypical chromosome, or heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical pair of mammal allosomes, determine the sex of an individual created in sexual reproduction. Autosomes differ from allosomes because autosomes appear in pairs whose members have the same form but differ from other pairs in a diploid cell, whereas members of an allosome pair may differ from one another and thereby determine sex. Nettie Stevens and Edmund Beecher Wilson both independently discovered sex chromosomes in 1905.

Genes borrowed from viruses and mobile genetic elements (MGEs) have recently been identified as playing a crucial role in the differentiation of multicellular tissues and organs and even in sexual reproduction, in the fusion of egg cell and sperm.Rafi Letzter: An Ancient Virus May Be Responsible for Human Consciousness, in: Live Science, February 02, 2018 Such fused cells are also involved in metazoan membranes such as those that prevent chemicals crossing the placenta and the brain body separation.Eugene V. Koonin: Viruses and mobile elements as drivers of evolutionary transitions. In: Philos Trans R Soc Lond B Biol Sci., 2016 Aug 19, doi:10.1098/rstb.2015.0442 Two viral components have been identified.

This diagram illustrates the twofold cost of sex. If each individual were to contribute the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) asexual population doubles in size each generation. Cell division generally takes place asexually by mitosis, a process that allows each daughter nucleus to receive one copy of each chromosome. Most eukaryotes also have a life cycle that involves sexual reproduction, alternating between a haploid phase, where only one copy of each chromosome is present in each cell and a diploid phase, wherein two copies of each chromosome are present in each cell.

Seedlings from sexual reproduction have a low survival rate; however, plantlets from the excised stem cuttings and leaf cuttings, broken off in the natural environment, are more successful. Cuttings have both water and carbon stored and available, which are resources needed for plant establishment. The detached part of the plant remains physiologically active, allowing mitotic activity and new root structures to form for water and nutrient uptake. Asexual reproduction of plants is also evolutionarily advantageous as it allows plantlets to be better suited to their environment through retention of epigenetic memory, heritable patterns of phenotypic differences that are not due to changes in DNA but rather histone modification and DNA methylation.

Chamaesyce albomarginata, the whitemargin sandmat, is a species with showy bracts, an adaptation to a semiarid region with competition for pollinators. Plants in the group (as with all other species in the genus Euphorbia) bear tiny flowering structures that look like single true flowers, as if each one were a flower with many stamens surrounding a single ovary. In fact, the structure is a cyathium (sometimes called a pseudanthium, meaning a "false flower"). It is made up of many small flowers, but with each flower reduced to only the functional organs of sexual reproduction: a single stamen or a single pistil without petals or sepals.

Example of DNA profiling in order to determine the father of a child (Ch). Child's DNA sample should contain a mixture of different size DNA bands of both parents. In this case person #1 is likely the father The DNA of an individual is the same in every somatic (nonreproductive) cell. Sexual reproduction brings the DNA of both parents together to create a unique combination of genetic material in a new cell, so the genetic material of an individual is derived from the genetic material of each parent in equal amounts; this genetic material is known as the nuclear genome of the individual, because it is found in the nucleus.

The decrease in fertility is also in part due to the education and counseling that both men and women receive in Iceland at a young age in sexual reproduction. Those who choose to have children are incentivized with progressive policies aiming at enhancing both emotional and physical stability and progress. Children have universal benefits in Iceland if they age 7 years of age or less. The Social Security System in Iceland re-affirms how critical these early years are for children especially in terms of instilling social and intellectual frameworks in the minds of children who will become the leaders of that same country as well as political activists.

Scale insects show a very wide range of variations in the genetics of sex determination and the modes of reproduction. Besides sexual reproduction, a number of different forms of reproductive systems are employed, including asexual reproduction by parthenogenesis. In some species, sexual and asexual populations are found in different locations, and in general, species with a wide geographic range and a diversity of plant hosts are more likely to be asexual. Large population size is hypothesized to protect an asexual population from becoming extinct, but nevertheless, parthenogenesis is uncommon among scale insects, with the most widespread generalist feeders reproducing sexually, the majority of these being pest species.

Laboratory studies that explicitly test for reinforcement are limited, with many of the experiments having been conducted on Drosophila fruit flies. In general, two types of experiments have been conducted: using artificial selection to mimic natural selection that eliminates the hybrids (often called "destroy-the- hybrids"), and using disruptive selection to select for a trait (regardless of its function in sexual reproduction). Many experiments using the destroy-the- hybrids technique are generally cited as supportive of reinforcement; however, some researchers such as Coyne and Orr and William R. Rice and Ellen E. Hostert contend that they do not truly model reinforcement, as gene flow is completely restricted between two populations.

The wild precursor of domesticated saffron crocus was likely Crocus cartwrightianus, which originated in Crete or Central Asia; C. thomasii and C. pallasii are other possible sources. Although some doubts remain on its origin, it is believed that saffron originated in Iran (Persia). However, Greece and Mesopotamia have also been suggested as the possible region of origin of this plant. The saffron crocus is now a triploid that is "self-incompatible" and male sterile; it undergoes aberrant meiosis and is hence incapable of independent sexual reproduction—all propagation is by vegetative multiplication via manual "divide-and-set" of a starter clone or by interspecific hybridisation.

Ventral view with hyperiid amphipod Almost entirely transparent and colorless, and sometimes difficult to resolve, Aequorea victoria possess a highly contractile mouth and manubrium at the center of up to 100 radial canals that extend to the bell margin. The bell margin is surrounded by uneven tentacles, up to 150 of them in fully-grown specimens. The tentacles possess nematocysts that aid in prey capture, although they have no effect on humans. Specimens larger than 3 cm usually possess gonads for sexual reproduction, which run most of the length of the radial canals and are visible in the photos in this article as whitish thickenings along the radial canals.

ABC model of flower development guided by three groups of homeotic genes. The ABC model of flower development is a scientific model of the process by which flowering plants produce a pattern of gene expression in meristems that leads to the appearance of an organ oriented towards sexual reproduction, a flower. There are three physiological developments that must occur in order for this to take place: firstly, the plant must pass from sexual immaturity into a sexually mature state (i.e. a transition towards flowering); secondly, the transformation of the apical meristem's function from a vegetative meristem into a floral meristem or inflorescence; and finally the growth of the flower's individual organs.

The earliest reported observations of pollen under a microscope are likely to have been in the 1640s by the English botanist Nehemiah Grew, who described pollen and the stamen, and concluded that pollen is required for sexual reproduction in flowering plants. By the late 1870s, as optical microscopes improved and the principles of stratigraphy were worked out, Robert Kidston and P. Reinsch were able to examine the presence of fossil spores in the Devonian and Carboniferous coal seams and make comparisons between the living spores and the ancient fossil spores. Early investigators include Christian Gottfried Ehrenberg (radiolarians, diatoms and dinoflagellate cysts), Gideon Mantell (desmids) and Henry Hopley White (dinoflagellate cysts).

The modern evolutionary synthesis is based on the concept that populations of organisms have significant genetic variation caused by mutation and by the recombination of genes during sexual reproduction. It defines evolution as the change in allelic frequencies within a population caused by genetic drift, gene flow between sub populations, and natural selection. Natural selection is emphasised as the most important mechanism of evolution; large changes are the result of the gradual accumulation of small changes over long periods of time. The modern evolutionary synthesis is the outcome of a merger of several different scientific fields to produce a more cohesive understanding of evolutionary theory.

By cooperatively moving their flagella, choanocytes filter particles out of the water and into the spongocoel, and out through the osculum. This improves both respiratory and digestive functions for the sponge, pulling in oxygen and nutrients and allowing a rapid expulsion of carbon dioxide and other waste products. Although all cells in a sponge are capable of living on their own, choanocytes carry out most of the sponge's ingestion, passing digested materials to the amoebocytes for delivery to other cells. Choanocytes can also turn into spermatocytes when needed for sexual reproduction, due to the lack of reproductive organs in sponges (amoebocytes become the oocytes).

The germ cell population (~40 in mice), after specification, migrate to the developing gonads where they differentiate further into gametogonia. Much of the research in germ cell development is done on animal models. Animal models are an effective research tool due to the commonality of sexual reproduction which is thought to have same or similar mechanisms across species. The majority of research is done on mice which has led to advances in understanding germ line differentiation across all mammal but there are some species specific mechanisms which have not been studied as extensively due to the difficulty of both obtaining human samples and the ethical limitations of human research.

The species in this genus have two vertebrate hosts in their life cycle: a felid (the definitive host) and prey species (the intermediate host), which vary and depend on the local fauna but include mice, deer and others. In the gastrointestinal tract of the definitive host the parasite undergoes sexual reproduction, forms a zygote which after some divisions forms a cyst that is excreted. The cyst is subsequently ingested by the prey species in whom the parasite decysts and invades its tissues wherein it again multiplies and encysts. After ingestion of the tissues of the prey species by the definitive host the parasite again decysts and multiplies.

Some invertebrate species that feature (partial) sexual reproduction in their native range are found to reproduce solely by parthenogenesis in areas to which they have been introduced. Relying solely on parthenogenetic reproduction has several advantages for an invasive species: it obviates the need for individuals in a very sparse initial population to search for mates, and an exclusively female sex distribution allows a population to multiply and invade more rapidly, potentially up to twice as fast. Examples include several aphid species and the willow sawfly, Nematus oligospilus, which is sexual in its native Holarctic habitat but parthenogenetic where it has been introduced into the Southern Hemisphere.

Two decades later, Barbara McClintock and Harriet Creighton demonstrated that chromosomal crossover occurs during meiosis, the process of cell division by which sperm and egg cells are made. Within the same year as McClintock's discovery, Curt Stern showed that crossing over—later called "recombination"—could also occur in somatic cells like white blood cells and skin cells that divide through mitosis. In 1947, the microbiologist Joshua Lederberg showed that bacteria—which had been assumed to reproduce only asexually through binary fission—are capable of genetic recombination, which is more similar to sexual reproduction. This work established E. coli as a model organism in genetics, and helped Lederberg win the 1958 Nobel Prize in Physiology or Medicine.

The cause of this apparent lack of natural reproduction is not currently known, but the consequences are clear—it severely reduces the species' chance for long-term survival. Sexual reproduction of pondberry is critical for long-range dispersal and genetic diversity. Before modern flood control was imposed along the Mississippi River and its tributaries, historic floods may have been an important mechanism in fruit and/or seed dispersal over long distances or for creating suitable conditions for seedling establishment. Although the fruit of pondberry sinks in water after a short time, the seed with the pulp removed will float for a day or sometimes longer.Smith, Carl G., III; Hamel, Paul B.; Devall, Margaret S.; Schiff, Natan M. 2004.

Charles Darwin «The Variation of Animals and Plants Under Domestication», 1868 г.: > I will therefore give all the facts which I have been able to collect on the > formation of hybrids between distinct species or varieties, without the > intervention of the sexual organs. For if, as I am now convinced, this is > possible, it is a most important fact, which will sooner or later change the > views held by physiologists with respect to sexual reproduction. A > sufficient body of facts will afterwards be adduced, showing that the > segregation or separation of the characters of the two parent-forms by bud- > variation, as in the case of Cytisus adami, is not an unusual though a > striking phenomenon.

In one of these colonies, the protagonist is happily reunited with his long-lost beloved and they embark upon monogamous marriage and on having children through sexual reproduction and female pregnancy – an incredibly archaic and old-fashioned way of life for most of that time's humanity. Elizabeth A. Lynn's science fiction novel A Different Light (1978) features a same-sex relationship between two men, and inspired the name of the LGBT bookstore chain A Different Light. Lynn's The Chronicles of Tornor (1979–80) series of novels, the first of which won the World Fantasy Award, were among the first fantasy novels to include gay relationships as an unremarkable part of the cultural background. Lynn also wrote novels depicting sadomasochism.