All yeasts engage in asexual reproduction most of the time.
|
|
"Most of the clades on our own planet use asexual reproduction," Gatti noted.
|
|
With asexual reproduction, conversely, there's no need for men to tire themselves out.
|
|
About 50 vertebrates are known to use asexual reproduction including fish, amphibians and reptiles.
|
|
A variety of species of ants, wasps and bees can switch between sexual and asexual reproduction.
|
|
However, when there are no males around, asexual reproduction, despite its shortcomings, is the best option for species survival.
|
|
Amazon MollyImage: Manfred Schartl/TAMUOne thing you might think about asexual reproduction is that it's bad for genetic fitness.
|
|
Asexual reproduction in sharks happens when a polar body, or the cell adjacent to the egg fertilizes it, said Dudgeon.
|
|
Dudgeon described asexual reproduction as a "holding-on mechanism," passed down along generations of women until male partners are available.
|
|
In theory, just one female could have produced all the long-horned ticks spreading in the country through asexual reproduction.
|
|
Parthenogenesis — a natural form of asexual reproduction — is something that's common amongst plant species, insects, amphibians and many other life forms.
|
|
Some recovery efforts, like coral transplantation, are trying to make up for the damage by artificially redirecting coral's natural asexual reproduction process.
|
|
When tests showed that the pups were only carrying their mother's DNA, it became clear that the shark had likely achieved asexual reproduction.
|
|
"Asexual reproduction should dominate and sex should be rare because sex is enormously wasteful, primarily because males don't produce offspring, (at least not directly)," Auld says.
|
|
Switching from sexual to asexual reproduction is far less common, although not impossible, Dudgeon told The New Scientist, citing an eagle ray and boa constrictor who have done so.
|
|
There's also the more ethically comfortable idea of asexual reproduction, which would involve planting biophores on habitable—but uninhabited—worlds, where they could start a new riff on Earth life.
|
|
Garden snails, in particular, are capable of asexual reproduction, which means they're able to reproduce without another mate, but according to Davison, still prefer to get it on with another individual, if possible.
|
|
Leonie the leopard shark (also known as a zebra shark) from Reef HQ aquarium in Townsville, Australia, has stunned researchers by becoming the first of her species with a recorded mating history to switch to asexual reproduction.
|
|
"One theory is that in the wild, if for some reason males can't have contact with the females for one breeding season, they can keep their lineage going for one or two seasons [through asexual reproduction], until they can reproduce the traditional way," said Tristam.
|
|
Scientists said on Monday they have deciphered the genome of the Amazon molly, one of the few vertebrate species to rely upon asexual reproduction, and discovered that it had none of the genetic flaws, such as an accumulation of harmful mutations or a lack of genetic diversity, they had expected.
|
|
Vegetative reproduction usually takes place by fragmentation. Asexual reproduction is by flagellated zoospores. And haplospore, perrination (akinate and palmellastage). Asexual reproduction by mytospore absent in spyrogyra.
|
|
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.
|
|
Asexual reproduction makes the daughter cnidarian a clone of the adult.
|
|
Capable of asexual reproduction, P. orchidioides tends to be clump-forming.
|
|
Mammals are now the only major vertebrate group in which asexual reproduction has not been observed. Scientists say that asexual reproduction in the wild is rare, and probably a last-ditch effort to reproduce when a mate is not present. Asexual reproduction diminishes genetic diversity, which helps build defenses against threats to the species. Species that rely solely on it risk extinction.
|
|
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.
|
|
Ascomycetes: Ascomycetes are 'spore shooters'. They are fungi which produce microscopic spores inside special, elongated cells or sacs, known as 'asci', which give the group its name. Asexual reproduction: Asexual reproduction is the dominant form of propagation in the Ascomycota, and is responsible for the rapid spread of these fungi into new areas. Asexual reproduction of ascomycetes is very diverse from both structural and functional points of view.
|
|
Asexual reproduction may have contributed to the blue shark's decline off the Irish coast.
|
|
Archegonia are clustered and surrounded by a pesudoperianth. Asexual reproduction occurs via apical tubers.
|
|
Reproduction is only known by asexual reproduction. Species of Hemiselmis remain motile even while dividing.
|
|
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.
|
|
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.
|
|
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.
|
|
The process of sporic meiosis. Like all bryophytes, Fissidens adianthoides have sporic meiosis as well as asexual reproduction.
|
|
Jakoba use asexual reproduction by binary fission. The sexual reproduction or the formation of cysts have not been observed.
|
|
"True" parthenogenesis is a form of asexual reproduction in all-female species that produce offspring without any male involvement.
|
|
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.
|
|
This fungus grows hyphally and its asexual reproduction cycles have been well described in literature. Asexual reproduction occurs through its lens-shaped arthroconidia with thickened rings of cell wall material. Young colonies appear grey and turns purple-black as it matures. The conidiophores develop by dividing their branches into sections of equal length.
|
|
Eggs develop inside the body and are shed in capsules. Weeks later, the eggs hatch and grow into adults. In asexual reproduction, the planarian detaches its tail end and each half regrows the lost parts by regeneration, allowing neoblasts (adult stem cells) to divide and differentiate, thus resulting in two worms. Some researchers claim that the products derived from bisecting planaria are similar to the products of planarian asexual reproduction; however, debates about the nature of asexual reproduction in planaria and its effect on the population are ongoing.
|
|
Genetic analysis confirmed that her offspring was the product of automictic parthenogenesis, a form of asexual reproduction in which an ovum merges with a polar body to form a zygote without fertilization. Along with an earlier case of parthenogenesis in the bonnethead (Sphyrna tiburo), this event suggests that asexual reproduction may be more widespread in sharks than previously thought.
|
|
Apomixis is the process of asexual reproduction through seed, in the absence of meiosis and fertilization, generating clonal progeny of maternal origin.
|
|
The sexes are distinct and fertilisation is external. Asexual reproduction also occurs by fragmentation. When handled, this worm easily breaks into pieces.
|
|
This unique characteristic of asexual reproduction helped to develop a number of cultivars of fruits and vegetables including grapes, apples, pears and peaches.
|
|
Humans are the intermediate hosts in which asexual reproduction occurs, and female anopheline mosquitos are the definitive hosts harbouring the sexual reproduction stage.
|
|
The primary host, where the flukes sexually reproduce, is a vertebrate. The intermediate host, in which asexual reproduction occurs, is usually a snail.
|
|
Ethics of Health Care: An Introductory Textbook, page 127 (Georgetown University Press 2002). Further, identical twinning is an instance of asexual reproduction whereby a conceptus, without ceasing to be what it is (a new human being), provides a cell or cells as a new conceptus, entirely separated or partially separated (a 'siamese' twin) from the original conceptus, but in any event self-actuated in its development from the moment that the act of asexual reproduction (twinning) is complete. By this asexual reproduction, the parents of the original conceptus in effect become grandparents to the identical twin so conceived.
|
|
Retrieved 2012-02-11. A group of robust sea cucumbers on a reef in Bali, Indonesia Some Holothurians may reproduce asexually by fission. It was reported that C. robustus was capable of fission, but there was no evidence of asexual reproduction in natural populations. When placed in a tank under poor environmental conditions, however, asexual reproduction by fission was observed in C. robustus.
|
|
When cells divide, their full genome is copied and each daughter cell inherits one copy. This process, called mitosis, is the simplest form of reproduction and is the basis for asexual reproduction. Asexual reproduction can also occur in multicellular organisms, producing offspring that inherit their genome from a single parent. Offspring that are genetically identical to their parents are called clones.
|
|
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.
|
|
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.
|
|
Asexual reproduction by transverse fission has also been observed in adult sea cucumbers. Holothuria parvula uses this method frequently, an individual splitting into two a little in front of the midpoint. The two-halves each regenerate their missing organs over a period of several months but the missing genital organs are often very slow to develop. The larvae of some echinoderm species are capable of asexual reproduction.
|
|
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.
|
|
Bulbils in the leaf axils of Lilium lancifolium Seeds of Liliaceae species Methods of propagation include both sexual and asexual reproduction. Commercial cultivars are usually sterile.
|
|
Asexual reproduction also takes place, usually by transverse fission, and may result in groups of individuals clustered in close proximity to each other, sometimes tangled together.
|
|
In some plants, the diploid tissue of the nucellus can give rise to the embryo within the seed through a mechanism of asexual reproduction called nucellar embryony.
|
|
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.
|
|
Cyclic parthenogenesis is the primary mode of reproduction in D. pulicaria and other species within the genus Daphnia. Therefore, D. pulicaria are capable of switching between sexual and asexual reproduction based on environmental conditions. Typically, Daphnia undergo asexual reproduction when living in favorable conditions, such as in environments with abundant food or with negligible crowding. In contrast, they produce ephippia, which are dormant eggs, and reproduce sexually if environmental conditions worsen.
|
|
This oozoid develops further and takes on a quite different form than the gonozooid. Through asexual reproduction called budding, new gonozooids are produced and the life cycle closes.
|
|
P. cumingi reproduces either sexually or asexually. It is gonochoric (having separate sexes). Asexual reproduction, which results in a clonal offspring, occurs by fission, splitting the central disc.
|
|
In the British Isles, it is often encountered in a fertile state. Structures for asexual reproduction (gemmae) are also sometimes present on the edges of the leaves and bracts.
|
|
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.
|
|
This asexual reproduction is common amongst ferns. While it grows well in full shade, the fishbone waterfern will thrive in areas of full sun if enough water is available.
|
|
As this process is a form of asexual reproduction, it does not produce genetic diversity in the offspring. Therefore, these are more vulnerable to changing environments, parasites and diseases.
|
|
During asexual reproduction, the nucleus divides yielding two daughter cells one of which exits through the opening in the lorica. This new cell then synthesizes its own new lorica.
|
|
Pearsal and Loose (1937) reported the occurrence of motile cells in Chlorella. Bendix (1964) also observed that Chlorella produces motile cells which might be gametes. These observations have an important bearing on the concept of the life cycle of Chlorella, which at present is considered to be strictly asexual in character. Asexual reproduction in Chlorella ellipsoides has been studied in detail and the following four phases have been observed during the asexual reproduction.
|
|
Organism cloning (also called reproductive cloning) refers to the procedure of creating a new multicellular organism, genetically identical to another. In essence this form of cloning is an asexual method of reproduction, where fertilization or inter-gamete contact does not take place. Asexual reproduction is a naturally occurring phenomenon in many species, including most plants and some insects. Scientists have made some major achievements with cloning, including the asexual reproduction of sheep and cows.
|
|
Flora of North America. 2007 Gametophytes have substantial asexual reproduction by fragmentation, producing much of the living material in sphagnum peatlands.Rydin, Hakan and Jeglum, John K. 2006. Biology of Peatlands.
|
|
Asexual reproduction occurs through longitudinal division, wherein the plane of division is parallel to the groove in the cell. They are only able to divide after engulfing many other eukaryotes.
|
|
After fire, Melaleuca uxorum resprouts at the stem base and along stems from epicormic buds. The species forms small colonies which appear to have developed from both sexual and asexual reproduction.
|
|
Asexual reproduction from rhizomes is a common means of sustaining a population. It flowers in early to midsummer, usually with 1 to 2 flowers per stalk, less commonly 3 or 4.
|
|
Since it is a colonial coral, the polyp then goes through asexual reproduction to form more polyps, expanding the size of the coral colony and increasing the number of coral polyps.
|
|
Triploids may also persist through asexual reproduction. In fact, stable autotriploidy in plants is often associated with apomictic mating systems. In agricultural systems, autotriploidy can result in seedlessness, as in watermelons and bananas.
|
|
The NMFS published a recovery plan in March of 2015, which clearly outlined the conservation goals and efforts for Elkhorn coral. This document indicated that the main goals are to increase the abundance of this species and protect the genetic diversity throughout its entire range. This latter goal is especially important for conservation. Elkhorn coral are capable of both sexual and asexual reproduction; however, asexual reproduction is more common, which has resulted in only about 50% of Elkhorn being genetic individuals.
|
|
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.
|
|
They reproduce by asexual reproduction as current research concludes. Further studies can focus on whether Goniomonads are sexual. And, it is still to determine whether the biological species concept can be applied to them.
|
|
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.
|
|
Each female only produces 1 clutch per year. Females on Barrow Island reproduce by parthenogenesis, a form of asexual reproduction where the growth and development of the embryo occurs without fertilisation by a male.
|
|
Apomixis in flowering plants (angiosperms) includes some types of vegetative reproduction and also agamospermy, which is asexual reproduction through seedsWinkler, H. (1908). Über Parthenogenesis und Apogamie im Pflanzenreich. Progressus Rei Botanicae. 2(3): 293–454.
|
|
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.
|
|
The South American sea nettle is highly evolved, specifically within their sexual reproductive strategies. They have to undergo bodily changes in order to experience both sexual and asexual reproduction then go through a process called strobilation.
|
|
Anthopleura thallia has a patchy distribution but is locally abundant. It is likely that it is clonal as many individuals are scarred, having undergone asexual reproduction by splitting longitudinally. No zooxanthellae are found in this species.
|
|
A new polyp is usually formed within 14 days. The new polyps are clones of the original Aiptasia. Aiptasia diaphana can produce both male and female offspring through asexual reproduction. Some clones even develop into hermaphrodites.
|
|
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.
|
|
Kirk et al., p. 633. Environmental conditions trigger genetically determined developmental states that lead to the creation of specialized structures for sexual or asexual reproduction. These structures aid reproduction by efficiently dispersing spores or spore-containing propagules.
|
|
The other three being Disa aurata, Disa cardinalis, and Disa uniflora. Disa tripetaloides is able to reproduce sexually and asexually. Asexual reproduction occurs by means of creating offshoots along the base of the plant and on stolons.
|
|
Kirk et al., p. 633. Environmental conditions trigger genetically determined developmental states that lead to the creation of specialized structures for sexual or asexual reproduction. These structures aid reproduction by efficiently dispersing spores or spore-containing propagules.
|
|
This is a phenomenon of natural asexual reproduction, also denominated "vegetative reproduction". It is a strategy of plant propagation. The complex of clonal individuals and the originating plant comprise a single genetic individual, i. e., a genet.
|
|
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.
|
|
Asexual reproduction in the first larval stage is ubiquitous. While the sexual formation of the digenean eggs and asexual reproduction in the first larval stage (miracidium) is widely reported, the developmental biology of the asexual stages remains a problem. Electron microscopic studies have shown that the light microscopically visible germ balls consist of mitotically dividing cells which give rise to embryos and to a line of new germ cells that become included in these embryonic stages. Since the absence of meiotic processes is not proven, the exact definition remains doubtful.
|
|
Asexual reproduction occurs by the formation of uninucleate, haploid sporangiospores in the sporangia, on the terminal ends of the aerial sporangiophores. In the sporangia, there is an accumulation of nutrients, cytoplasm, and nuclei. An extension of the sporangiophore called the columella protrudes into the sporangium, and upon the maturation of the sporangiospores, burst of the sporangium allows for the dispersion of the spores, where wind is the primary dissemination method. Asexual reproduction may be favoured in unfavourable environmental conditions, as this inhibits the conjugation between the two sexual strains.
|
|
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.
|
|
Small narrow underleaves are present. Asexual reproduction occurs by gemmae can be found on the margins of the upper leaves. Mylia taylorii is dioecious but fertile plants are uncommon in Britain. The dark brown capsule is ovoid - globose.
|
|
The entire animal, including tentacles, is several meters long. The feeding polyps are pink when young, before developing tentacles. A mature feeding polyp is yellow with a single tentacle. Colonies are unisexual, and reproduce by incomplete asexual reproduction.
|
|
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.
|
|
These structures are commonly found in fungi, algae, liverworts and mosses, but also in some flowering plants such as pygmy sundews and some species of butterworts. Vascular plants have many other methods of asexual reproduction including bulbils and turions.
|
|
G. barretti is an oviparous species with separated males and females. The reproductive cycle is annual with one or two events of gamete release per year. The larvae has never been observed. Asexual reproduction has never been formally described.
|
|
In botany, "pseudogamy" is also related to asexual reproduction. Wilhelm Olbers FockeFocke, W.O. 1881. Die Pflanzen-mischlinge, ein Beitrag zur Biologie der Gewächse. Borntraeger, Berlin. Google books (1881) is usually cited for the definition of the term.Hermsen, J.G.T. (1980).
|
|
Many algae similarly switch between sexual and asexual reproduction. A number of plants use both sexual and asexual means to produce new plants, some species alter their primary modes of reproduction from sexual to asexual under varying environmental conditions.
|
|
Developmental biology is the study of the process by which animals and plants grow and develop. Developmental biology also encompasses the biology of regeneration, asexual reproduction, metamorphosis, and the growth and differentiation of stem cells in the adult organism.
|
|
Deep-water corals use nematocysts on their tentacles to stun prey. Deep-water corals feed on zooplankton, crustaceans and even krill. Coral can reproduce sexually or asexually. In asexual reproduction (budding) a polyp divides in two genetically identical pieces.
|
|
In a purebred strain or breed, the goal is that the organism will "breed true" for the breed-relevant traits. Apomixis and parthenogenesis, types of asexual reproduction, also result in true breeding, although the organisms are usually not homozygous.
|
|
Apomixis is asexual reproduction through seeds and does not require pollination. It is distributed throughout the monocot clade in Poales, Asparagales, Liliales, Dioscoreales, and Alismatales. Thus apomixis may have evolved once in a basal ancestor and has since repeatedly become lost.
|
|
Chrysaora hysoscella utilize both sexual and asexual reproduction throughout development. Mature individuals reproduce sexually by broadcast spawning. Males release sperm from their mouths into the water column. Females fertilize the sperm internally and can fertilize sperm from multiple male partners.
|
|
Additionally, Schizocyathus fissilis has an unusual method of asexual reproduction known as parricidal budding. This is a process in which a new polyp develops on the inner surface of a fragment of a parent corallite that has split apart longitudinally.
|
|
Psalteriomonas undergoes asexual reproduction with closed mitotic division. In other words, during mitosis, the nuclear envelope stays intact. The nucleus elongates while an intranuclear spindle is formed. The nucleolus remains inside of the nucleus and divides into two during the process.
|
|
Very few fruits reach maturity, and many immature fruits can often be seen lying on the ground below. This plant reproduces mainly through seeds, but its tubercles may break off and have a chance of producing new plants through asexual reproduction.
|
|
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.
|
|
In zoology it means a type of parthenogenesis in which the sperm stimulates the egg cell to develop into an embryo, but no genes from the male are inherited. Gynogenesis is a synonym.Engelstädter, J. (2008). Constraints on the evolution of asexual reproduction. BioEssays.
|
|
The life cycle of Spironucleus involves one active trophozoite stage and one inactive cyst stage. Spironucleus undergoes asexual reproduction via longitudinal binary fission. Spironucleus vortens can cause lateral line erosion in freshwater anglefish . Spironucleus columbae is found to cause hexamitiasis in pigeons .
|
|
It involves karyogamy, the formation of a zygote, which is followed by meiosis and multiple fission. This results in the production of sporozoites. Other forms of replication include ' and '. Endodyogeny is a process of asexual reproduction, favoured by parasites such as Toxoplasma gondii.
|
|
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.
|
|
The conidia are thick-walled, globose to barrel-shaped, brown to black, and typically found with coarse surface ornamentation, dehiscing by schizolysis. Ramoconidia are absent. Colonies on MLA grow slowly and are dark in pigmentation. Synanamorphs are absent during its asexual reproduction stages.
|
|
The flowers are dioecious, and are hidden in the middle of the plant amongst the leaves. Small green berries form after successful fertilization. The plant can also undergo asexual reproduction. Mother and daughter plants are connected by a short stolon, forming dense mats.
|
|
They drift with the plankton, and after a few days, they settle on the seabed, attach themselves to the substrate and become juvenile sponges. Asexual reproduction is via budding, or by fragmentation, a process that occurs when pieces of sponge become detached.
|
|
In 2008 water soldier plant was reported found along the shore line. The plant is imported from Europe. It is a common pond plant, purchased in garden stores. It has sharp leaves and is a possible concern as the plant spreads quickly using asexual reproduction.
|
|
One inflorescence may have over 100 spikelets. The plant is dioecious, with male and female flowers on separate plants. Some populations lack male plants, while others are able to reproduce sexually. Asexual reproduction is more common than sexual, and most populations are all female.
|
|
It is a characteristic feature of cnidarians. For example, Obelia has feeding individuals, the gastrozooids; the individuals capable of asexual reproduction only, the gonozooids, blastostyles; and free-living or sexually reproducing individuals, the medusaearyana. Balanced polymorphism refers to the maintenance of different phenotypes in population.
|
|
A conoid is found in most species and when present forms complete but truncated cone. Sexual and asexual reproduction are present in life cycle of all species. Each zygote normally forms an oocyst wall within which it undergoes meiosis. This is sometimes followed by mitosis.
|
|
Bacteria and archaea reproduce through asexual reproduction, usually by binary fission. Genetic exchange and recombination still occur, but this is a form of horizontal gene transfer and is not a replicative process, simply involving the transference of DNA between two cells, as in bacterial conjugation.
|
|
Aiptasia can reproduce both sexually and asexually. Asexual reproduction occurs when a small segment is separated from the pedal disk. A single cell can be enough for a new Aiptasia anemone to form. The separated segment will start growing and develop a new polyp.
|
|
This restricted, granular appearance with a reddish-brown reverse colony makes it distinguished from other species in the genus. Cylindrical or oblong conidia are produced in asexual reproduction. Conidia are pale yellow-orange, smooth to slightly rugose. Both intercalary and apical conidia were observed.
|
|
Cytoplasmic organization and rhythmic streaming in growing blades of Caulerpa prolifera Retrieved August 18, 2011. Under normal conditions, asexual reproduction occurs by fragmentation of the plant. Pieces of tissue only a few millimetres across are capable of growing into new plants.Ceccherelli, G., L. Piazzi.
|
|
Gynogenesis is a form of asexual reproduction in which female eggs are activated by male sperm, but no male genetic material is contributed to offspring. While this mode of reproduction has not been observed in reptiles, it occurs in several salamander species of the genus Ambystoma.
|
|
Ceratiums have zygotic meiosis in their alternation of generation. Ceratium dinoflagellates may reproduce sexually or asexually. In asexual reproduction, the pellicle (shell) pulls apart and exposes the naked cell. The cell then increases in size and divides, creating 4–8 daughter cells, each with two flagella.
|
|
They secrete cellulase, which is used for digesting wood. The next subgroup, Trichomonadida, does not require oxygen and possesses hydrogenosomes. They only reproduce through asexual reproduction and some strains are human pathogens. There are three types of pathogenic parabasalia: Trichomonas foetus, Dientamoeba fragilis, and Trichomonas vaginalis.
|
|
With the onset of favourable conditions (such as warm winter months), they can germinate to form a new individual. As these processes are all forms of asexual reproduction, they do not produce genetic diversity in the offspring. Therefore, asexual reproduced Oedogonium are more vulnerable to changing environments.
|
|
Eleuteroschisis is asexual reproduction in dinoflagellates in which the parent organism completely sheds its theca (i.e. undergoes ecdysis) either before or immediately following cell division. Neither daughter cell inherits part of the parent theca.FENSOME R.A., TAYLOR F.J.R., NORRIS G., SARJEANT W.A.S., WHARTON D.I. & WILLIAMS G.L. 1993.
|
|
However, growth rates vary enormously both between strains and between environments. Mean replicative lifespan is about 26 cell divisions. In the wild, recessive deleterious mutations accumulate during long periods of asexual reproduction of diploids, and are purged during selfing: this purging has been termed "genome renewal".
|
|
Membrane glyconjugates have been proposed as potential host cell receptors for Eimeria species. After invasion, the sporozoites develop into trophozoites, then into schizonts, where they undergo several rounds of asexual reproduction. This results in many nuclei developing within the schizont. Each nucleus develops into a merozoite.
|
|
Once attached the planula larva starts metamorphosis and becomes a polyp. This polyp will reproduce asexually, most commonly using budding, and producing ephryae which mature into a medusa to begin the life cycle process over again. Scyphozoans and Drymonema species alternate between sexual and asexual reproduction stages.
|
|
Flora of North America. This plant occurs in many types of habitat, including desert shrublands and scrubs, grassland, meadows, pinyon-juniper woodland, oak and pine woodlands, riparian habitat, sagebrush, and disturbed areas. The species exhibits agamospermy, asexual reproduction via seeds. Many, but not all, individuals are polyploid.
|
|
Asexual reproduction occurs mainly vegetatively by mitosis and budding. Saccharomycotina is characterized by holoblastic budding, which means all layers of the parent cell wall are involved in the budding event. This leaves a scar through which no further budding occurs. Asexual cells may vary in shape.
|
|
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.
|
|
There is no clear division between thorax and abdomen, which collectively bear five pairs of appendages. The shell surrounding the animal extends posteriorly into a long or short spine. Like most other Daphnia species, D. pulex reproduces by cyclical parthenogenesis, alternating between sexual and asexual reproduction.
|
|
Doliolids also have circular muscles, the sudden contraction of which cause them to move rapidly in a characteristic jerky manner.Pelagic Tunicates JelliesZone. Retrieved 2011-11-17. They have a complex life cycle, as do other doliolids, with forms that alternate between generations that undergo sexual and asexual reproduction.
|
|
Strobilisation or transverse fission is a form of asexual reproduction consisting of the spontaneous transverse segmentation of the body. It is observed in certain cnidarians and helminths. This mode of reproduction is characterized by high offspring output, which, in the case of the parasitic tapeworms, is of great significance.
|
|
Fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning where an organism is split into fragments. Each of these fragments develop into mature, fully grown individuals that are clones of the original organism. In echinoderms, this method of reproduction is usually known as fissiparity.
|
|
After post-ingestion hatching or penetration of the snail, the miracidium metamorphoses into a simple, sac-like mother sporocyst. The mother sporocyst undergoes a round of internal asexual reproduction, giving rise to either rediae (sing. redia) or daughter sporocysts. The second generation is thus the daughter parthenita sequence.
|
|
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.
|
|
The tetrasporophyte occurs throughout the year, but is most common between October and March. It was at one time thought to be a different species and was given the name Trailliella intricata. Vegetative reproduction is uncommon, but asexual reproduction occurs as a result of fragmentation of the thallus.
|
|
Blakeslea trispora undergoes both sexual and asexual reproduction. The asexual reproductive phase of Blakeslea trispora involves the production of sporangiospores produced in sporangia. Once released, they can germinate in the presence of free water. Colonies of B. trispora grow rapidly on the agar growth media at 25 °C.
|
|
Of the many issues involved, there is widespread agreement on the following: the advantage of sexual and hermaphroditic reproduction over asexual reproduction lies in the way recombination increases the genetic diversity of the ensuing population.Smith, John Maynard. 1998. Evolutionary Genetics (2nd ed.). Oxford: Oxford U. Pr.p234Gillespie J.G. 2004.
|
|
The sporozoites undergo two waves of schizogeny (asexual reproduction) in the crypts and produce many first and second generation merozoites. These merozoites can invade locally and reproduce themselves to produce a smaller variety of schizonts. The sporozoites are then shed in the feces and the process begins again.
|
|
Journal of Industrial Microbiology 2, 59-62. Besides the asexual reproduction mode, under certain conditions (e.g. nutritional stress) Z. bailii produces sexual spores (ascospores) in a sac called ascus (plural: asci). Normally, each ascus contains one to four ascospores, which are generally smooth, thin-walled, spherical or ellipsoidal.
|
|
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.
|
|
The parasites are transmitted by tick bite. After a cat or other host is bitten by an infected tick the parasites infect mononuclear phagocytes. Within these they undergo asexual reproduction (schizonts). As these leukocytes become engorged with schizonts, they line the lumens of veins and may causing obstruction of blood flow.
|
|
Many organisms, including aspen trees, reproduce by cloning, often creating large groups of organisms with the same DNA. One example depicted here is quaking aspen. Cloning is the process of producing individuals with identical or virtually identical DNA, either naturally or artificially. In nature, many organisms produce clones through asexual reproduction.
|
|
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.
|
|
The presence of HAP2 induces hemifusion and the mixing of cell content. Yet when considering asexual reproduction, somatic cells can also undergo cell-cell fusion or self-fusion. Two particular fusogens observed were SO and MAK-2. Evidence supports that these proteins control and regulate efficient protein concentration and localization.
|
|
This cooling cycle must be implemented in captivity or females will lay eggs continuously, resulting in calcium depletion, poor health, and even death. Although there is no confirmed cases of asexual reproduction in crested geckos, there has been claims of females laying eggs with no sexual activity with a male.
|
|
Academic Press. For instance, for influenza, the infectious propagules are carried in droplets of host saliva or mucus that are expelled during coughing or sneezing. In horticulture, a propagule is any plant material used for the purpose of plant propagation. In asexual reproduction, a propagule is often a stem cutting.
|
|
When the eggs hatch, they develop in to rediae. These undergo asexual reproduction and multiply before becoming motile cercariae. The cercariae are few in number and large in size, in comparison to their small gastropod host. They emerge from the snail into the water at night and become free-living.
|
|
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.
|
|
Intermediate hosts such as cattle or pigs then ingest sporocysts. Sporozoites are then released in the body and migrate to vessels, where they undergo the first two generation of asexual reproduction. These rounds result in the development of meronts. This stage lasts about 15 to 16 days after ingestion of sporocysts.
|
|
The life cycle is similar to Toxoplasma. An infected dog will pass the oocysts through its feces and infect food or water. A cow or other animal will then up take the parasite. The parasite will undergo asexual reproduction in the animal's muscle until it is eaten by a dog.
|
|
Another constraint on switching from sexual to asexual reproduction would be the concomitant loss of meiosis and the protective recombinational repair of DNA damage afforded as one function of meiosis.Avise, J. (2008) Clonality: The Genetics, Ecology and Evolution of Sexual Abstinence in Vertebrate Animals. See pp. 22-25. Oxford University Press.
|
|
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.
|
|
Males can mate about 18 days after maturation, and females produce oothecae about every 8 days, beginning about 55 days after maturation. The oothecae are buried in soil or decaying logs, and hatch in 50 days at . Parthenogenesis (asexual reproduction) can occur, but the nymphal clones do not develop to adulthood.
|
|
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.
|
|
Creolimax is one of the few ichthyosporeans that is culturable. It can be easily grown in the lab through cycles of asexual reproduction. Each cycle comprises two stages. First, a growth stage, in which the cells, which are non-motile, contain several nuclei, a cell wall, and a big central vacuole.
|
|
Apomictically produced offspring are genetically identical to the parent plant. Some authors included all forms of asexual reproduction within apomixis, but that generalization of the term has since died out. In flowering plants, the term "apomixis" is commonly used in a restricted sense to mean agamospermy, i.e., clonal reproduction through seeds.
|
|
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.
|
|
Sato, A., Bishop, J. & Holland, P. (2008). Developmental Biology of Pterobranch Hemichordates: History and Perspectives. Genesis, 46:587-591. Astogeny happens when the colony grows through asexual reproduction from the tip of a permanent terminal zooid, behind which the new zooids are budded from the stalk, a type of budding called monopodial.
|
|
During asexual reproduction N. sphaerica releases spores known as conidia. The conidia are ejected out forcefully at maximum horizontal distances of 6.7 cm, and 2 cm vertically. Discharge of spores occurs in all directions. The mechanism for projection relies on the conidiophore consisting of a flask-shaped support cell that bears the conidium.
|
|
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.
|
|
Aspergillus versicolor has long, septate hyphae that appear glassy and transparent. Conidiphores, which are specialized hyphal stalks for asexual reproduction, typically measure 120–700 μm in length. Conidiophores terminate in small vesicles (10–15 μm in diameter) that are biseriate (i.e., with two successive layers of cells interposing the vesicle and conidia).
|
|
Namacalathus has typically been considered to represent a cnidarian-grade organism, due in part to its propensity for asexual reproduction by budding. Most recently, however (2015), it been interpreted as a lophophorate based on detailed observations of its skeletal construction, which point to accretionary growth in the manner of brachiopods and bryozoans.
|
|
This is a form of asexual reproduction found in females, where growth and development of embryos occurs without fertilization by a male. Eggs are oval or barrel-shaped, like seeds. Different types of oviposition occur in leaf insects. The eggs of this species are catapulted by a backward movement of the abdomen.
|
|
The potential for asexual reproduction is possible. Like most echinoderms, I. fuscus has a unique regenerative ability. Induced transverse fission has been experimented in a lab setting. The results were successful, showing a high survival rate, and a complete regeneration of anterior and posterior body parts in a maximum of three months.
|
|
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).
|
|
Avian hosts release fluke eggs along with their excreta, which will land on surrounding vegetation for snails to consume. The miracidia will hatch and bore through the snail’s digestive tract. The sporocyst will penetrate and entangle the internal organs of the snail. The sporocysts will continue to grow and multiple by asexual reproduction.
|
|
Staghorn corals are hermaphrodites. They are mostly broadcast-spawners and some species have been involved in annual synchronous mass-spawning events on the Great Barrier Reef and in Japanese and Indonesian waters. Some species undergo fragmentation, a form of asexual reproduction, and this sometimes results in reefs composed of a single species.
|
|
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.
|
|
Comparison of life cycles and morphology of Cyanea nozakii and other scyphozoans. Plankton and Benthos Research 3:118–124.Feng S, Zhang G-T, Sun S, Zhang F, Wang S-W, Liu M-T. 2015. Effects of temperature regime and food supply on asexual reproduction in Cyanea nozakii and Nemopilema nomurai. Hydrobiologia 754:201–214.
|
|
The ascospores contained in the asci are smooth, refractive spheres with a glassy appearance, about 3.6-4.3 μm in diameter. Most ascospores produced by the ascomata are not viable. In asexual reproduction, the fungus forms conidiophores through mitosis. Conidiophores are septate and break into cylindrical arthrospores 3-6 μm long and 3-4 μm wide.
|
|
Pocillopora verrucosa, like many corals, contains microscopic symbiotic dinoflagellate algae (zooxanthellae) living within its tissues. Through photosynthesis, these algae produce energy-rich molecules that the coral can assimilate. It has been found that these algae are already present in the eggs before spawning. Pocillopora verrucosa can reproduce by fragmentation, a form of asexual reproduction.
|
|
Pygmy sundew Drosera roseana with gemmae. A gemma (plural gemmae) is a single cell, or a mass of cells, or a modified bud of tissue, that detaches from the parent and develops into a new individual. This type of asexual reproduction is referred to as fragmentation. It is a means of asexual propagation in plants.
|
|
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.
|
|
It has also been suggested that cloning may occur to make use of the tissues that are normally lost during metamorphosis. Recent research has shown that the larvae of some sand dollars clone themselves when they detect predators (by sensing dissolved fish mucus). Asexual reproduction produces many smaller larvae that escape better from planktivorous fish.
|
|
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.
|
|
This invasion kills some of the leaf cells and the leaf will develop a lesion followed by necrosis. If the conditions are favourable, the mould will undergo asexual reproduction and produce a tree of sporangiophores out of the leaf. The sporangiophores will produce conidia that can be dispersed by the wind to another plant.
|
|
Still, "Phycomycetes" can be used to refer to all the above-mentioned classes as a whole. The members of this group are found in aquatic habitats and on decaying wood in moist and damp places or as obligate parasites on plants. The mycelium is aseptate and coenocytic. Asexual reproduction by zoospore or by aplanospore.
|
|
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.
|
|
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.
|
|
Asexual reproduction in Baltic Sea populations is accomplished by the production of adventitious branches that come loose and reattach to the bottom by the formation of rhizoids. Adventitious branches are present in thalli of F. vesiculosus also in other areas, but asexual formation of new thalli has never been reported outside the Baltic Sea.
|
|
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.
|
|
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.
|
|
This method of growing creates "growth rings" which can be used to estimate the age of a colony. Asexual reproduction can also occur if a branch breaks off and a replacement is needed. Though light is not required for growth or development, mature colonies will grow towards light. Why they do so is unknown.
|
|
Induced plantlet-forming species have the LEC1 gene that allows them to produce seeds, whereas the constitutive plantlet-forming species have a defective LEC1 gene and cannot produce seeds.Garces, Helena M. P. “Evolution of asexual reproduction in leaves of the genus Kalanchoe.” Proc Natl Acad Sci U S A 104. 39 (2007): 15578-83.
|
|
As with other Rubus species, its seeds are readily distributed by birds. It can also propagate, or asexual reproduction, itself through cutting. It can grow in open fields or in canopies of moist forests. The Himalayan raspberry can also support large populations of Drosophila, or fruit flies, from its rotting fruit, and its fruits are also consumed by elephants.
|
|
The infection cycle first starts with the ingestion of a free-swimming dinospore by a copepod. Rather than being digested, the dinospore grows and developed into a parasitic trophocyte. At this stage, it takes residence in the copepod's gut lumen, where it competes for nutrients and organic matter. Following infection, the trophocyte will engage in asexual reproduction by palintomy.
|
|
When the species is facing more stress from the environment in there is a selective pressure for apomixis, or asexual reproduction, which may give an answer to this plant's tendency to have an uneven ploidy number. On average, in the Draba genus the higher the elevation and latitude of the species the more ploidy the species possesses.
|
|
The silica skeleton of a diatom cell (called the frustule) consists of an epitheca and an hypotheca. The hypotheca is slightly smaller than the epitheca. During asexual reproduction both thecae form the epitheca of the new daughter cell and each daughter produces a new hypotheca. Therefore one daughter cell is always smaller than the original cell.
|
|
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.
|
|
Telogaster opisthorchis reproduce via sexual and asexual reproduction. Males have testis which produce sperm and have a very primitive vas deferens. During copulation, sperm is ejaculated out of the male and into the female uterus where it is stored in the seminal receptable and fertilization of the eggs occur. After fertilization, meiosis occurs and development begins.
|
|
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.
|
|
Bryum is a polyphyletic genus that has high morphological variation. Bryum species generally have shorter laminal cells with short, thick, and rounded stems. All Bryum species exhibit narrowed cells at the margins. Bryum species can be identified through patterns of asexual reproduction, coloration features of the stem and leaf base, and the strength of the leaf border.
|
|
50px Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. This type of asexual reproduction is unique among the colonial volvocine green algae (Pocock 1953). By contrast, in Eudorina, protoplast rotation is lacking during successive divisions; a spheroidal colony is formed by means of inversion after successive divisions.
|
|
Methods of asexual reproduction include both budding and the formation of gemmules. In budding, aggregates of cells differentiate into small sponges that are released superficially or expelled through the oscula. Gemmules are found in the freshwater family Spongellidae. They are produced in the mesohyl as clumps of archeocytes, are surrounded with a hard layer secreted by other amoebocytes.
|
|
In 1909, while studying chloroplast genomes, Erwin Baur made the first observations about organelle inheritance patterns. Organelle genome inheritance differs from nuclear genome, and this is illustrated by four violations of Mendel's laws. # During asexual reproduction, nuclear genes never segregate during cellular divisions. This is to ensure that each daughter cell gets a copy of every gene.
|
|
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.
|
|
Though coral have large sexually-reproducing populations, their evolution can be slowed by abundant asexual reproduction. Gene flow is variable among coral species. According to the biogeography of coral species gene flow cannot be counted on as a dependable source of adaptation as they are very stationary organisms. Also, coral longevity might factor into their adaptivity.
|
|
Holoplankton have unique traits that make reproduction in the water column possible. Both sexual and asexual reproduction are used depending on the type of plankton. Some invertebrate holoplankton release sperm into the water column which are then taken up by the females for fertilization. Other species release both sperm and egg to increase the likelihood of fertilization.
|
|
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.
|
|
The neck is where asexual reproduction of proglottid segments occurs. Proglottid segments are individual sets of reproductive organs that compose the rest of the cestode body. The most posterior section of the cestode body consists of multiple strobila, each being made up of several proglottids. There are 3 stages that proglottids go through in their maturation.
|
|
Drosera regia also produces relatively few thick, fleshy roots, which possess root hairs along the terminal . Asexual reproduction of mature plants usually occurs after flowering with new plants arising from the rhizome and roots. After a fire, undamaged roots will often re-sprout new plants. Drosera regia flowers in January and February, producing scapes up to long.
|
|
Academia Sinica. Issue 1, 23:89-104. These filamentous cell's life cycles include both sexual and asexual reproduction, depending on life cycle stage. Although quite common, Oedogonium is difficult to identify, since key ID factors are only present during reproduction, which is an uncommon life stage among this genus. David, M.J. 2003: Freshwater Algae of North America.
|
|
The plume anemone can also increase its numbers by asexual reproduction. An individual can undergo binary fission by splitting in half and growing into two organisms. Or it can develop buds which grow into new individuals before becoming detached. Fragmentation, also known as basal laceration, is another mechanism by which the number of individuals can be increased rapidly.
|
|
Cuttings are used as a method of asexual reproduction in succulent horticulture, commonly referred to as vegetative reproduction. A cutting can also be referred to as a propagule. Succulents have evolved with the ability to use adventitious root formation in reproduction to increase fitness in stressful environments. Succulents grow in shallow soils, rocky soils, and desert soils.
|
|
The sporocysts rapidly multiply by asexual reproduction, each forming numerous daughter sporocysts. The daughter sporocysts move to the liver and gonads of the snail, where they undergo further growth. Within 2–4 weeks, they undergo metamorphosis and give rise to fork-tailed cercariae. Stimulated by light, hundreds of cercariae penetrate out of the snail into water.
|
|
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.
|
|
Polysphondylium pallidum starts life as a single-celled amoeboid protist. Like other slime moulds, it lives in soil, dung, leaf litter and other decaying organic materials. It is known as a myxamoeba and feeds on bacteria and fungal spores. In favourable, damp conditions it may reproduce sexually while in drier conditions, asexual reproduction is more likely.
|
|
Many protists and fungi alternate between sexual and asexual reproduction. A few species of amphibians, reptiles, and birds have a similar ability. The slime mold Dictyostelium undergoes binary fission (mitosis) as single-celled amoebae under favorable conditions. However, when conditions turn unfavorable, the cells aggregate and follow one of two different developmental pathways, depending on conditions.
|
|
Asexual reproduction is found in nearly half of the animal phyla. Parthenogenesis occurs in the hammerhead shark and the blacktip shark. In both cases, the sharks had reached sexual maturity in captivity in the absence of males, and in both cases the offspring were shown to be genetically identical to the mothers. The New Mexico whiptail is another example.
|
|
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.
|
|
The queen is succeeded by asexual reproduction, in which an aged queen lays eggs with no openings for sperm to enter through, effectively making a clone of herself . All individuals have part of their eyes developed, but the size increases if the individual is on a reproductive tract. Individuals have been shown to cannibalize injured nestmates.
|
|
In California it is more severe in coastal areas. Research was undertaken to see whether spores from the telemorph, Gibberella circinata, might be responsible for spread of the fungus. It was found that very few vegetative compatibility groups existed among the California strains of the pathogen. This implied that asexual reproduction predominated and laboratory tests confirmed this.
|
|
The sporangiospores are asexual mitospores (formed via mitosis), produced inside sporangia (thousands of spores) or sporangioles (single or few spores). They are released when mature by the disintegration of the sporangium wall, or as a whole sporangiole that separates from the sporangiophore. The sporangiospores germinate to form the haploid hyphae of a new mycelium. Asexual reproduction often occurs continuously.
|
|
Aquilonastra burtoni is a species of small sea star from the family Asterinidae from the Red Sea which has colonised the eastern Mediterranean by Lessepsian migration through the Suez Canal, although the Mediterranean populations are clonal reproducing through fissiparous asexual reproduction. It was originally described in 1840 by the English zoologist and philatelist John Edward Gray.
|
|
There is a possible connection between polyploidy (having more than two copies of one's chromosomes) and perenniality. One potential explanation is that both polyploids (larger in size) and asexual reproduction (common in perennials) tend to be selected for in inhospitable extremes of a species' distribution. One example could be the intricate polyploidy of native Australian perennial Glycine species.
|
|
Its adaptation to dim light is assisted by its containing two accessory photosynthetic pigments, the green-absorbing carotenoids siphonein and siphonaxanthin, as well as chlorophyll a and chlorophyll b. In Florida, reproductive events occurred simultaneously across the reef, with up to 5% of thalli developing gametangia. Asexual reproduction also occurred through fragmentation or the growth of vegetative stolons.
|
|
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).
|
|
The reproductive cycle of red algae may be triggered by factors such as day length. Red algae reproduce sexually as well as asexually. Asexual reproduction can occur through the production of spores and by vegetative means (fragmentation, cell division or propagules production). In Archibald, J. M., In Simpson, A. G. B., & In Slamovits, C. H. (2017).
|
|
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.
|
|
Cryptococcosis, sometimes informally called crypto, is a potentially fatal fungal disease caused by a few species of Cryptococcus (most often Cryptococcus neoformans or Cryptococcus gattii). Cryptococcosis is believed to be acquired by inhalation of the infectious propagule from the environment. Although the exact nature of the infectious propagule is unknown, the leading hypothesis is the basidiospore created through sexual or asexual reproduction.
|
|
Marchantia with round cups, and Lunularia with crescent cups, both containing gemmae. Gemmae dislodged by rain are visible at the bottom of the image. The production of gemmae is a widespread means of asexual reproduction in both liverworts and mosses. In liverworts such as Marchantia, the flattened plant body or thallus is a haploid gametophyte with gemma cups scattered about its upper surface.
|
|
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.
|
|
At cooler temperatures, asexual reproduction took place in multi-chambered "mitosporangia". The gametophyte phase only produces gametes when day length is long; with shorter days these too reproduce asexually. This is probably because the plants upon which they are epiphytic only grow in the spring. The gametophyte is filamentous – while the sporophyte bears parenchyma, even though it only reaches around in length.
|
|
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.
|
|
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.
|
|
During this process, the organism is known as a ' or '. Cytokinesis next subdivides the multinucleated schizont into numerous identical daughter cells called merozoites (see glossary below), which are released into the blood when the host cell ruptures. Organisms whose life cycles rely on this process include Theileria, Babesia, Plasmodium, and Toxoplasma gondii. Sporogony is a type of sexual and asexual reproduction.
|
|
E. lineata is the only known member of the Edwardsiidae family to have a parasitic life stage. Upon fertilization, a primary planula develops. Instead of direct development into an adult polyp like many other anemone species such as its close relative Nematostella vectensis Hand C, Uhlinger KR. The Culture, Sexual and Asexual Reproduction, and Growth of the Sea Anemone Nematostella vectensis. Biol Bull.
|
|
Plasmodia of this genera have only been seen to undergo mitosis in culture conditions. Asexual reproduction through multiple fission, where the nuclei will undergo many rounds of mitotic division before the cytoplasm separates. In Reticulomyxa, mitosis is closed, the nuclear membrane remains intact during spindle formation and chromosome separation. Under culture conditions, division was initiated following the movement to a new location.
|
|
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).
|
|
S. candida is a hyaline mold with septate hyphae. The white and membranous morphology of S. candida colonies differentiates it from the more common species S. brevicaulis, which is characterized by a sand-coloured and granular colonial morphology. As the colony ages, it becomes slightly yellow. Conidiophores are specialized hyphal stalks that have conidiogenous cells which produce conidia for asexual reproduction.
|
|
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.
|
|
The amount of variation generated can be adjusted in many different ways, for example via the mutation rate, via the probability of sexual vs. asexual reproduction, via the probability of outcrossing vs. inbreeding, via dispersal, and via access to previously cryptic variants through the switching of an evolutionary capacitor. A large population size increases the influx of novel mutations in each generation.
|
|
The rabbits ingest sporulated oocysts. Sporulated oocysts contain sporozoites that hatch and travel via the hepatic portal vein to the liver, and eventually penetrate the bile duct epithelium, where they undergo asexual reproduction known as schizogony. Rupture of the schizont consequently causes epithelial cell rupture and death. Merozoites will penetrate other cells and create more merozoites for one to several rounds.
|
|
Asexual reproduction is mostly by fragmentation, when part of a colony becomes detached and reattaches elsewhere. Stony corals occur in all the world's oceans. Much of the framework of modern coral reefs is formed by scleractinians. Reef-building or hermatypic corals are mostly colonial; most of these are zooxanthellate and are found in the shallow waters into which sunlight penetrates.
|
|
Montastraea annularis can be fragmented to form new colonies. The most common means of asexual reproduction in colonial stony corals is by fragmentation. Pieces of branching corals may get detached during storms, by strong water movement or by mechanical means, and fragments fall to the sea bed. In suitable conditions, these are capable of adhering to the substrate and starting new colonies.
|
|
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 most important and general is production of conidia, but chlamydospores are also frequently produced. Furthermore, Ascomycota also reproduce asexually through budding. #Conidia formation: Asexual reproduction may occur through vegetative reproductive spores, the conidia. The asexual, non-motile haploid spores of a fungus, which are named after the Greek word for dust (conia), are hence also known as conidiospores and mitospores.
|
|
The larvae are brooded initially and later released into the sea when they are well enough developed. They soon settle on the seabed, turn themselves inside out and cement themselves in place before undergoing metamorphosis. Each colony is entirely formed by the asexual reproduction of this founding zooid and subsequent clonal budding. Different zooids in the colony have different specialised functions.
|
|
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.
|
|
There are two forms of asexual reproduction in this species. The first is fragmentation where the bryophyte is broken into completely separate pieces and grows to become a new individual from the parent plant. The second method is regeneration from caducous organs. This is when the organs of the plant such as leaves, shoots, leaf apices, and branches detach from the parent shoot.
|
|
While solitary individuals bear all of those energy costs, individuals in some social colonies share a portion of those costs. Modular organisms save energy by using asexual reproduction during their life. Energy reserved in this way allows them to put more energy towards colony growth, regenerating lost modules (due to predation or other cause of death), or response to environmental conditions.
|
|
Fungi commonly produce spores, as a result of sexual, or asexual, reproduction. Spores are usually haploid and grow into mature haploid individuals through mitotic division of cells (Urediniospores and Teliospores among rusts are dikaryotic). Dikaryotic cells result from the fusion of two haploid gamete cells. Among sporogenic dikaryotic cells, karyogamy (the fusion of the two haploid nuclei) occurs to produce a diploid cell.
|
|
Phoronis ovalis is believed to be a hermaphrodite, and the embryos are brooded in the tube. Asexual reproduction can also take place, either by budding or by transverse fission. The lophophore is used for feeding and for gas exchange. Under adverse conditions, the lophophore is readily autotomised; the animal can regenerate its lophophore and the shed lophophore can grow a new body.
|
|
The haploid generation consists of male and female gametophytes. The fertilization of egg cells varies between species of brown algae, and may be isogamous, oogamous, or anisogamous. Fertilization may take place in the water with eggs and motile sperm, or within the oogonium itself. Certain species of brown algae can also perform asexual reproduction through the production of motile diploid zoospores.
|
|
Linckia guildingi "comet", a starfish regrowing from a single arm Fragmentation is a form of asexual reproduction where a new organism grows from a fragment of the parent. Each fragment develops into a mature, fully grown individual. Fragmentation is seen in many organisms. Animals that reproduce asexually include planarians, many annelid worms including polychaetes and some oligochaetes, turbellarians and sea stars.
|
|
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.
|
|
Human red blood cell infected by the malaria parasite Plasmodium falciparum, showing a residual body with brown hemozoin. During its intraerythrocytic asexual reproduction cycle Plasmodium falciparum consumes up to 80% of the host cell hemoglobin. The digestion of hemoglobin releases monomeric α-hematin (ferriprotoporphyrin IX). This compound is toxic, since it is a pro-oxidant and catalyzes the production of reactive oxygen species.
|
|
Members of this genus are generally hermaphrodites. The male and female gametes may not be released simultaneously and sperm may be drawn into the vascular system of another individual. Fertilisation is internal and the ciliated larvae are liberated into the water column and become part of the zooplankton. Asexual reproduction also takes place, either by budding or through the development of gemmules.
|
|
Seeds accumulate over prolonged periods, and soil seed banks may be viable for 50–100 years. Asexual reproduction is achieved by sprouting, and often thickets of pin cherry plants form. The pin cherry is rather short lived, having a lifespan of only 20 to 40 years following a rapid maturation. Its root system is shallow, with roots tending to grow laterally.
|
|
Following this, male and female organs called the antheridia and archegonia will produce sperm and eggs through mitosis. If fertilization is successful, a diploid zygote will form, eventually developing into a dependent sporophyte, which will produce the following generation of spores. Due to the often short-lived nature of their habitat, members of Splachnaceae do not usually engage in asexual reproduction.
|
|
Research has been done to investigate these mechanisms has led to new discoveries of properties of this eukaryote and general properties of nuclear dimorphism. Tetrahymena have two major parts of their life cycle. there is an asexual reproduction stage involving binary fission as well as a non-reproductive sexual stage called conjugation. During this conjugation stage, the micronucleus cell undergoes meiosis.
|
|
Relationships within the genus are unclear, and some eastern North American species, including Boechera laevigata, may belong to a clade distinct from the rest of the genus. A very interesting feature of many species of the genus is asexual reproduction, a process known as apomixis. Microsatellite data has revealed that some of the apomictic lineages are hybrids between two or more sexual parents.
|
|
This species is also capable of asexual reproduction through longitudinal fission. In essence, an anemone will split into two pieces, and each will become a genetic copy of the other. Burrowing anemones are carnivores, eating unwary crabs that wander into their stinging tentacles. They are in turn preyed upon by the nudibranch Aeolidia papillosa, and likely other nudibranchs and small fish as well.
|
|
The unsporulated oocyst is shed from an infected bird in the feces. This exposure to air and moisture triggers meiosis and cell division. After 9–12 hours of sporulation (asexual reproduction by the production and release of spores) eight haploid sporozoites are formed. It has completed the sporulation stage after about 24 hours and can now infect a new host.
|
|
Aiptasia diaphana catches passing invertebrates, marine larvae and small fish with its tentacles, immobilising the prey with its cnidocytes (stinging cells). It also obtains nourishment from the zooxanthellae in its tissues. These photosynthetic algae manufacture carbohydrates in sunlight and these nutrients are available to the sea anemone. Aiptasia diaphana reproduces by both sexual and asexual reproduction and does so under different conditions.
|
|
The larger males do so more often than do the females, and this may account for the fact that there is an excess of males in the population.Mladenov, P.V.; Emson, R.H. (1988). Density, size structure and reproductive characteristics of fissiparous brittle stars in algae and sponges: evidence for interpopulational variation in levels of sexual and asexual reproduction. Marine ecology progress series.
|
|
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.
|
|
Aiptasia mutabilis has been known to reproduce both asexually and sexually. Although both methods are used, asexual reproduction has been most commonly seen in this species. To reproduce asexually, the anemone splits the column and separates. These two separate parts will adhere to a substrate and individuals will begin to develop from these smaller amounts of tissue from the original individual.
|
|
Agamospermy, asexual reproduction through seeds, occurs in flowering plants through many different mechanisms and a simple hierarchical classification of the different types is not possible. Consequently, there are almost as many different usages of terminology for apomixis in angiosperms as there are authors on the subject. For English speakers, Maheshwari 1950Maheshwari, P. 1950. An introduction to the embryology of the angiosperms.
|
|
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.
|
|
Astomes (order Astomatida) are a group of ciliate eukaryotes commonly found in the guts of annelid worms, especially oligochaetes, and other invertebrates. As their name implies, these parasites are characterized by an absence of mouth. The cell is covered by uniform cilia; in addition, some astomes attach themselves to their hosts by suckers, while others use various hooks or barbs. Asexual reproduction is by transverse fission.
|
|
Botrychium pumicola is a mycorrhizal fern, and grows sporophytic gemmae (i.e., little structures for the asexual reproduction of the sporophytic, or diploid, phase of the plant's life cycle). Some botanists believe that the gemmae might be adaptations to a dry climate and fires. Another name for plants of the genus Botrychium is 'grapeferns,' since the sexual reproductive structures (synangia) look like tiny yellow-green grapes.
|
|
It is such an aggressive sponge that it is considered likely that, in areas where it is present, branching and foliose corals may come to out-number massive corals in the long term. When a colonised coral dies and crumbles, parts of the sponge in the excavated tunnels may break up and detached pieces may become established in a new location, a form of asexual reproduction.
|
|
Blastodinium have a dinokaryon nucleus, characterized by a lack of histones and permanently condense chromosomes. Blastodinium perform closed mitosis, in which their nuclear envelope remains intact to aid in the orientation and segregation of chromosomes. Mitosis does not involve kinetochores or centrioles, as their chromosomes are attached to the inner membrane. During asexual reproduction, their mitosis stages follow one another in the absence of interphase.
|
|
Individual corals are either male or female. Fecundity is high and broadcast spawning takes place four to eight times per year. Asexual reproduction by fission is an important means of reproduction for this species. The coral may be fragmented due to physical forces, such as storms, but it is also capable of autotomy, causing itself to break apart through selective weakening of certain parts of the skeleton.
|
|
Bacteria evolve in a similar process to other organisms. This is through the process of natural selection, whereby beneficial adaptations are passed onto future generations until the trait becomes common within the entire population. However, bacteria reproduce via binary fission, which is a form of asexual reproduction meaning the daughter cell and the parent cell are genetically identical. This makes bacteria susceptible to environmental pressures.
|
|
Ricordea yuma are capable of both sexual and asexual reproduction. They have been observed asexually reproducing through marginal budding, a process where sections of the margin of the coral’s oral disk, including tentacles and a replicated mouth, elongate and detach from the mother coral. This may be why they are able to quickly overtake sections of substrate and become the dominant coral species after a disturbance.
|
|
Lophiostoma is a genus of ascomycetous fungi in the family Lophiostomataceae. Species are commonly found growing both on living and dead wood, bark of deciduous trees, on shrubs and on herbaceous hosts. They are also found in freshwater, and marine environments. The genus both forms fruit bodies with sexual reproducing with ascocarp in the form of a perithecium and asexual reproduction in the form of conidia.
|
|
Sex usually increases genetic variation and may increase the rate of evolution. This diagram illustrates the twofold cost of sex. If each individual were to contribute to the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) Asexual reproduction population doubles in size each generation. The two-fold cost of sex was first described by John Maynard Smith.
|
|
The large macrozooids can transform into swarmers and leave the colony. They settle on suitable surfaces and develop into new colonies. The microzooids are small cells specialized for feeding, which the colony does by consumption of their symbiotic bacteria and other organic particles. At the terminal ends of the colony are specialized zooids that can elongate and facilitate the asexual reproduction of the colony.
|
|
Lesions can have both the filamentous and vesicular type grains at the same time. Although conidation, a form of asexual reproduction, in M. mycetomatis is rare, two main types can be described in-vitro. In the first type oval to pyriform conidia, 3 to 5 µm can be observed. The conidia have truncated bases and are on the tips of simple or branched conidiophores.
|
|
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.
|
|
C. uncinata goes through asexual reproduction for cell division and duplication called amitosis. As C. uncinata has two nuclei, it goes through two different styles of division of the nuclei. The germ-line nucleus goes through mitosis during asexual division while the somatic nucleus undergoes amitosis. Amitosis is a stochastic process where unlike in mitosis, there is no spindle formation to segregate chromosomes during nuclear division.
|
|
Species within these genera exhibit both sexual and asexual reproduction, high heteriozygosity, ploidies from 2x to 6x, and gene flow between bordering populations as evidence of ongoing introgression. However, this gene flow is only made possible in the presence of B. intermedia, which introgression moves towards, and the absence of which keeps the other species reproductively isolated. B. intermedia is identified as the compilospecies in this model.
|
|
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.
|
|
It is likely asexual reproduction was not found in natural populations because the conditions were not stressful enough. Therefore, Colochirus robustus can reproduce both sexually and asexually. In the latter case, fission can take place with a transverse crack developing halfway along the body and gradually widening until the two halves split apart. The posterior end then grows a new anus while the anterior end develops a mouth and new tentacles.
|
|
Numerous maple cultivars that have been selected for particular characteristics can be propagated only by asexual reproduction such as cuttings, tissue culture, budding or grafting. Acer palmatum (Japanese maple) alone has over 1,000 cultivars, most selected in Japan, and many of them no longer propagated or not in cultivation in the Western world. Some delicate cultivars are usually grown in pots and rarely reach heights of more than 50–100 cm.
|
|
Didemnum molle is a suspension feeder. Water is drawn into the body of each zooid through the numerous buccal siphons, phytoplankton, zooplankton and fine organic particles are filtered out and the water is exhaled through the atrial siphon. Asexual reproduction takes place by budding. A new bud will form and begin to actively feed while the zooid from which it emerged gradually regresses and is eventually re-adsorbed.
|
|
One species of seastar, Ophidiaster granifer, reproduces asexually by parthenogenesis. In certain other asterozoans, the adults reproduce asexually for a while before they mature after which time they reproduce sexually. In most of these species, asexual reproduction is by transverse fission with the disc splitting in two. Regrowth of both the lost disc area and the missing arms occur so that an individual may have arms of varying lengths.
|
|
This has long been known to occur among starfish and brittle stars but has been more recently observed in a sea cucumber, a sand dollar and a sea urchin. These species belong to four of the major classes of echinoderms except crinozoans (as of 2011). Asexual reproduction in the planktonic larvae occurs through numerous modes. They may autotomise parts that develop into secondary larvae, grow buds or undergo paratomy.
|
|
Underside. The fan-shaped segments can break off and form a new polyp, a form of asexual reproduction. Cycloseris distorta is a solitary, free-living coral that grows to a diameter of about . The large polyp is irregular in shape and has a central mouth from which radiate wedge-shaped segments. The corallite (the stony cup in which the polyp sits) has numerous beaded septa (partitions) of varying heights.
|
|
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.
|
|
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.
|
|
Both juveniles and adults form groups of varying size. Like other members of its family, the blacktip shark is viviparous; females bear one to 10 pups every other year. Young blacktip sharks spend the first months of their lives in shallow nurseries, and grown females return to the nurseries where they were born to give birth themselves. In the absence of males, females are also capable of asexual reproduction.
|
|
It has a diploid life cycle which includes both sexual and asexual reproduction. In the asexual phase, a spore of Saprolegnia releases zoospores. Within a few minutes, this zoospore will encyst, germinate and release another zoospore. This second zoospore has a longer cycle during which most dispersal happens; it will continue to encyst and release a new spore in a process called polyplanetism until it finds a suitable substrate.
|
|
The life cycle of coccolithophores is characterized by an alternation of diploid and haploid phases. They alternate from the haploid to diploid phase through syngamy and from diploid to haploid through meiosis. In contrast with most organisms with alternating life cycles, asexual reproduction by mitosis is possible in both phases of the life cycle. Both abiotic and biotic factors may affect the frequency with which each phase occurs.
|
|
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.
|
|
Maturity is reached at a body length of about and spawning mostly takes place during the summer and autumn although in equatorial waters it may take place all year round. Holothuria atra is also fissiparous, meaning that it can reproduce by transverse fission.C. Conand, Asexual reproduction by fission in Holothuria atra: variability of some parameters in populations from the tropical Indo-Pacific, Oceanologica acta, 1996, vol. 19, no 3-4, pp.
|
|
Desmoschisis is asexual reproduction in dinoflagellates which the parent cell divides to produce two daughter cells, each daughter retaining half the parent theca, at least temporarily. During desmoschisis, the theca undergoes fission along a predetermined suture between thecal plates. The fission suture is oblique, usually from the top left to the bottom right (as in oblique binary fission).FENSOME R.A., TAYLOR F.J.R., NORRIS G., SARJEANT W.A.S., WHARTON D.I. & WILLIAMS G.L. 1993.
|
|
Inquiry into the evolution of aging aims to explain why so many living things and the vast majority of animals weaken and die with age (exceptions include Hydra and the already cited jellyfish Turritopsis dohrnii, which research shows to be biologically immortal). The evolutionary origin of senescence remains one of the fundamental puzzles of biology. Gerontology specializes in the science of human aging processes. Organisms showing only asexual reproduction (e.g.
|
|
Clonal Fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning where an organism is split into fragments. Each of these fragments develop into mature, fully grown individuals that are clones of the original organism. In echinoderms, this method of reproduction is usually known as fissiparity. Due to many environmental and epigenetic differences, clones originating from the same ancestor might actually be genetically and epigenetically different.
|
|
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.
|
|
Related plants like sorghum and gamma grass are able to perform apomixis, a form of asexual reproduction that keeps the plant's DNA intact. This trait is apparently controlled by a single dominant gene, but traditional breeding has been unsuccessful in creating asexually-reproducing maize. Genetic engineering offers another route to this goal. Successful modification would allow farmers to replant harvested seeds that retain desirable traits, rather than relying on purchased seed.
|
|
Freshwater sponges reproduce both sexually and asexually, exhibiting two methods of asexual reproduction: by gemmules and by budding. Gemmules: Gemmules are elaborate, highly-resistant resting stages formed by freshwater sponges. Gemmules can be produced at any time during the growing season, but most production occurs in the autumn, triggered by seasonal changes in light and temperature. They form by migration of food-filled archaeocytes, also called amoebocytes, into discrete masses.
|
|
The replicator dynamics models heredity but not mutation, and assumes asexual reproduction for the sake of simplicity. Games are run repetitively with no terminating conditions. Results include the dynamics of changes in the population, the success of strategies, and any equilibrium states reached. Unlike in classical game theory, players do not choose their strategy and cannot change it: they are born with a strategy and their offspring inherit that same strategy.
|
|
The colonies co-ordinate their flagellar movement to create a rolling, swimming motion. Pandorina shows the beginnings of the colony polarity and differentiation seen in Volvox since the anterior cells have larger eyespots. Molecular sequencing has shown that Pandorina is paraphyletic with respect to Volvulina. Asexual reproduction is by simultaneous division of all cells of the colony to form autocolonies that are liberated by a gelatinization of the colonial envelope.
|
|
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.
|
|
Examples of gonochoric or dioecious pollination include hollies and kiwifruit. In these plants the male plant that supplies the pollen is referred to as the pollenizer. Gonochorism stands in contrast to other reproductive strategies such as asexual reproduction and hermaphroditism. The sex of an individual may also change during its lifetime – this sequential hermaphroditism can for example be found in parrotfishBester, C. Stoplight parrotfish Florida Museum of Natural History, Ichthyology Department.
|
|
Controlled reciprocal pollinations between P. occidentalis and P. orientalis resulted in good yields of germinable seed and true hybrid seedlings. Crosses of both species, as females, with P. racemosa and P. wrightii produced extremely low yields of germinable seed, but true hybrids were obtained from all interspecific combinations. Apomixis (asexual reproduction from non-fertilized seeds) appeared common in P. orientalis.Bean. Trees and Shrubs Hardy in the British Isles.
|
|
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.
|
|
This species is a highly peculiar fish in regard to its evolution and reproduction. It has been derived from hybridisation between females of Squalius pyrenaicus and males of another, unknown cyprinid species, and maintains the genomes of both parental species. Squalius alburnoides may have various numbers of these genomes (polyploidy), and may use different reproductive modes to pass them on to the offspring, including asexual reproduction, normal meiosis and hybridogenesis.
|
|
Life cycle of Balantidium coli Trophozoite and cyst stages are shown in the life cycle of Balantidium coli the causative agent of balantidiasis. In the apicomplexan life cycle the trophozoite undergoes schizogony (asexual reproduction) and develops into a schizont which contains merozoites. The trophozoite life stage of Giardia colonizes and proliferates in the small intestine. Trophozoites develop during the course of the infection into cysts which is the infectious life stage.
|
|
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.
|
|
These live off the yolk sac for about twenty-four days before settling and starting filter feeding.Reproduction of a Northumberland population of the polychaete Cirratulus cirratus Asexual reproduction by means of clones growing from the posterior of the worm have been recorded, but the taxonomic status of Cirratulus is under constant review and this report may refer to a different species.Petersen, M.E., (1999). Reproduction and development in Cirratulidae (Annelida: Polychaeta). Marine Biology, 8, 243-259.
|
|
Bryophyllum daigremontianum with plantlets on one of the leaves Chlorophytum comosum "Variegatum" in a hanging basket showing the plantlets Plantlets are young or small clones, produced on the leaf margins or the aerial stems of another plant. Many plants such as spider plants naturally create stolons with plantlets on the ends as a form of asexual reproduction. Vegetative propagules or clippings of mature plants may form plantlets. An example is mother of thousands.
|
|
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.
|
|
Pogonatum urnigerum is a dioicous plant that reproduces by spore dispersal. The spores are dispersed over a period of time by the movement of wind or the plant's peristome teeth. Annual growth increments can be found on the stem of this species of moss that resemble the rings of trees. Pogonatum urnigerum does not specialize in asexual reproduction as it lacks gemmae cups and caducous structures that would help itself to asexually reproduce.
|
|
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.
|
|
In the first intermediate host, the miracidium undergoes asexual reproduction for several weeks, which includes sporocyst formation, a few generations of rediae and the production of cercariae. The cercariae are released from the snail host into water and are also free- swimming. The cercariae penetrate a second intermediate host, or they remain in the first intermediate host, where they form metacercariae. Definitive hosts become infected by eating secondary hosts which are infected with metacercariae.
|
|
Like other Scyphozoans, Chrysaora hysoscella undergo metamorphosis as the organism develops and experiences a polyp and then medusa form. Females release planular larvae which swim to find a suitable place to settle. The planulae attach to a benthic substrate and develop into a sessile polyp which releases immature medusae through asexual reproduction called strobilation. Chrysaora hysoscella function as a male upon maturity and then develop female gametes, meaning this organism is protandrously hermaphroditic.
|
|
Ulluku (Ullucus tuberosus) tubers Tubers are enlarged structures in some plant species used as storage organs for nutrients. They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing season, and as a means of asexual reproduction. Stem tubers form thickened rhizomes (underground stems) or stolons (horizontal connections between organisms). Common plant species with stem tubers include the potato and yam.
|
|
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.
|
|
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.
|
|
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.
|
|
The capsule, which is only about 2–3 mm in length, contains the spores used in asexual reproduction and is made up of four peristome teeth. The capsule usually fruits around early summer and the green, papillose spores are spread by wind. The main contrast between T. pellucida and T. geniculta is the characteristics of the setae. In T. pellucida the setae are smooth and straight while in T. geniculta they are bent and papillose.
|
|
The organism goes through asexual reproduction phase that is called schizogony which occurs in the mononuclear phagocytic cells. In the tissue phase the macrophage cells that are infected often clog venules in organs such as the liver, spleen, lungs, and lymph nodes. It is this phase that is associated with clinical disease if the schizonts are numerous. Schizonts next form merozoites that break out of the macrophage cells and infect the red blood cells (erythrocytes).
|
|
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.
|
|
During the next 5–16 days, these sporozoites mature and divide by asexual reproduction into schizonts. Schizonts are structures that contain thousands of haploid merozoites, and rupture to release merozoites into the circulatory system. These merozoites then infect the red blood cells (erythrocytes) where they consume the hemoglobin of the red blood cells for energy and become immature, ring stage trophozoites. The trophozoites act as an intermediate stage, from which two forms can be formed.
|
|
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.
|
|
They emerge from unfertilized eggs. Phylogenetic analysis shows that the asexual species in the genus are not a monophyletic group; indicating that asexual reproduction evolved several times or that sexuality re-evolved. The asexual species have a high level of genetic diversity considering that they are clones; this may have arisen through hybridization and mutation. In at least two species, namely Bryobia kissophila and B. praetiosa, asexuality is caused by the parasitic bacterium Wolbachia.
|
|
Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment of the parent plant or a specialized reproductive structure. Many plants naturally reproduce this way, but it can also be induced artificially. Horticulturalists have developed asexual propagation techniques that use vegetative plant parts to replicate plants. Success rates and difficulty of propagation vary greatly.
|
|
Wallemia sebi has transparent hyphae, that are usually 1.5–2.5 µm wide, forming a compact mycelium. Conidiphores, the specialized stalks for asexual reproduction, are arranged in a parallel fashion and are usually unbranched. The conidiogenous cells are cylindrical and produce arthrospore-like conidia in packages of four. Conidia are cylindrical initially and soon become spherical in shape, approximately 2–2.5 µm in diameter, and form long bending chains up to 1 mm long.
|
|
The two polyps thus created then generate their missing body parts and exoskeleton. Transversal division occurs when polyps and the exoskeleton divide transversally into two parts. This means one has the basal disc (bottom) and the other has the oral disc (top); the new polyps must separately generate the missing pieces. Asexual reproduction offers the benefits of high reproductive rate, delaying senescence, and replacement of dead modules, as well as geographical distribution.
|
|
Asexual reproduction is the dominant form of propagation in the Ascomycota, and is responsible for the rapid spread of these fungi into new areas. It occurs through vegetative reproductive spores, the conidia. The conidiospores commonly contain one nucleus and are products of mitotic cell divisions and thus are sometimes called mitospores, which are genetically identical to the mycelium from which they originate. They are typically formed at the ends of specialized hyphae, the conidiophores.
|
|
According to Tanja Schwander, "Timema are indeed the oldest insects for which there is good evidence that they have been asexual for long periods of time." She heads a team of researchers who found that five Timema species (T. douglasi, T. monikense, T. shepardi, T. tahoe and T. genevievae) have used only asexual reproduction for more than 500,000 years, with T. tahoe and T. genevievae reproducing asexually for over one million years.
|
|
Some fungus chambers are shallow whereas others can be found in great depths, as deep as 2 meters. The abandoned chambers are used to deposit waste from the fungus garden and loose soil from chamber construction. The number of nest chambers tends to increase as colonies grow older. Because M. smithii queens are capable of asexual reproduction, it is believed that colonies can also grow by budding in addition to independent colony foundation.
|
|
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.
|
|
Many bacteria reproduce through binary fission, which is compared to mitosis and meiosis in this image. Unlike in multicellular organisms, increases in cell size (cell growth) and reproduction by cell division are tightly linked in unicellular organisms. Bacteria grow to a fixed size and then reproduce through binary fission, a form of asexual reproduction. Under optimal conditions, bacteria can grow and divide extremely rapidly, and bacterial populations can double as quickly as every 9.8 minutes.
|
|
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.
|
|
Asexual reproduction via zoospore is also very common and occurs in vegetative (benthic) cells. Vegetative cells produce zoosporangia – the enclosure in which spores are formed – which give rise to the zoospores. Each zoospore has a small hyaline anterior region, and at the base of this region is a ring of flagella (~150). Once emerged from the zoosporangium, a zoospore is still enveloped by a fragile vesicle, from which it is soon discharged.
|
|
It reproduces by asexual reproduction only, but it is capable of growing extremely quickly, starting from small fragments and doubling in dry weight every 2.2–2.5 days. It grows from fragments that have broken off or dormant buds that have been detached from the main plant. Each node has five buds so potential for great and rapid spread is high. It also produces spores but they are genetically defective and do not produce viable offspring.
|
|
Even when a colony is sexually reproductive, a large proportion of polyps remain infertile, which demonstrates the greater importance of asexual reproduction and growth. Z. sociatus colonies do not become reproductive until they reach a certain size. They use external fertilization, and are mostly hermaphroditic, although some are male or protogynous (female and then male). Z. sociatus was found to reproduce seasonally in Panama, and synchronizes the release of gametes with extremely low tides.
|
|
Nematogens proliferate in young cephalopods, filling the kidneys. As the infection ages, perhaps as the nematogens reach a certain density, vermiform larvae mature to form rhombogens, the sexual life stage, rather than more nematogens. This sort of density-responsive reproductive cycle is reminiscent of the asexual reproduction of sporocysts or rediae in larval trematode infections of snails. As with the trematode asexual stages, a few nematogens can usually be found in older hosts.
|
|
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.
|
|
Engorged female H. longicornis, dorsal view, about 10 mm long The seasonal feeding and reproductive cycle resembles that of other ticks. The tick can reproduce sexually or by an asexual process called parthenogenesis. The latter exist in northern Japan and Russia, whereas the former exist in southern Japan, southern Korea and southern parts of the former Soviet Union. An aneuploid race capable of both sexual and asexual reproduction capability exists in China.
|
|
The rediae burst out from the sporocyst to become the next-stage larvae called cercaria. This system of asexual reproduction allows for an exponential multiplication of cercaria individuals from one miracidium. This aids the fluke in reproduction, because it enables the miracidium to capitalize on one- chance occasion of passively being eaten by a snail before the egg dies. The mature cercariae bore out of the snail body into the freshwater environment.
|
|
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 Oedogoniales are an order of filamentous freshwater green algae of the class Chlorophyceae. The order is well-defined and has several unique features, including asexual reproduction with zoospores that possess stephanokont flagella: numerous short flagella arranged in a subapical whorl. The oedogoniales have a highly specialized type of oogamy, and an elaborate method of cell division which results in the accumulation of apical caps. The order comprises one family, Oedogoniaceae, with three genera.
|
|
Aquilonastra conandae is a species of starfish from the family Asterinidae found near the Mascarene Islands in the Indian Ocean. It is known for its asexual reproduction and is fissiparous. It is a small starfish, discrete and camouflaged, and occurs in coral reefs in the surf zone of large waves. The species was described in 2006 by Australian marine biologists P. Mark O'Loughlin and Francis Winston Edric Rowe, and gets its name from Chantal Conand.
|
|
Dictyostelium discoideum is a widely used model for cooperation and the development of multicellularity. This species of amoeba are most commonly found in a haploid, single-celled state that feed independently and undergo asexual reproduction. However, when the scarcity of food sources cause individual cells to starve, roughly 10⁴ to 10⁵ cells aggregate to form a mobile, multicellular structure dubbed a "slug". In the wild, aggregates generally contain multiple genotypes, resulting in chimeric mixtures.
|
|
C. meneghiniana splits in half during asexual reproduction. The halves are separated by the distinction between the two valves for each cell. Each of the two offspring that arise as a result of cell division have one of the two valves from the parent cell. During the separation of the parent cell, the cytoplasm forms the two offspring valves that will end up complementing the inherited parent valves in the offspring once reproduction is complete.
|
|
Agave schottii is a clonal plant, meaning it has the ability to clone itself and produce genetically identical offspring vegetatively. This method of asexual reproduction is not favorable as it produces offspring with low heterozygosity, or low genetic diversity. Experimentation shows that this plant favors outbreeding with an optimal range between 10 and 100 meters (33 feet and 330 feet). The greater the proximity of cross-breeders, the lower the genetic diversity.
|
|
Asexual reproduction produces many daughter (secondary) sporocysts which are called cecariacysts, that eventually release cercariae. Unlike most digenetic trematodes, Bucephalus Polymorphus lacks a redial stage and thus emerges as a cecaria directly from the sporocyst stage. Rapid proliferation of sporocysts results in a knotted white mass of tubules, which is found primarily in the gonads of the mussel. Released from the infected mussels, cercariae attach to fish (second intermediate host), encyst, and transforms into metacercariae.
|
|
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.
|
|
The asexual, all-female whiptail species Aspidoscelis neomexicanus (center), which reproduces via parthenogenesis, is shown flanked by two sexual species having males, A. inornatus (left) and A. tigris (right), which hybridized naturally to form A. neomexicanus. Parthenogenesis (; from the Greek + Liddell, Scott, Jones. γένεσις A.II, A Greek-English Lexicon, Oxford: Clarendon Press, 1940. q.v..) is a natural form of asexual reproduction in which growth and development of embryos occur without fertilization by sperm.
|
|
A solitary bee pollinating an Allium monocot flower. The monocots (or Monocotyledons) are one of the two major groups of flowering plants (or Angiosperms), the other being the dicots (or dicotyldons). In order to reproduce they utilize various strategies such as employing forms of asexual reproduction, restricting which individuals they are sexually compatible with, or influencing how they are pollinated. Nearly all reproductive strategies that evolved in the dicots have independently evolved in monocots as well.
|
|
These centrioles have a fixed position in the cell and play an important role in asexual reproduction. The entire cell is covered in thousands of flagella which arise from basal bodies. There are several patterns of how the flagella attach to the cell at the posterior end of the rostrum. In some species the flagella attach exclusively to the rostrum while in others the flagella attach to the rostrum, as well as adhering to each other.
|
|
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.
|
|
A sporocyst that contains germinal cells forms in the snail's body cavity, and, following asexual reproduction, produces rediae. Rediae produce cercariae (the larval form of the parasite). The cercariae migrate from the snail to a crab, entering either through direct penetration or by the consumption of the snail by the crab. Often, multiple species of Paragonimus can be found coexisting in one crustacean, suggesting that metacercariae of different species do not compete with each other within the host.
|
|
Parthenogenesis is a mode of asexual reproduction in which offspring are produced by females without the genetic contribution of a male. Among all the sexual vertebrates, the only examples of true parthenogenesis, in which all- female populations reproduce without the involvement of males, are found in squamate reptiles (snakes and lizards). There are about 50 species of lizard and 1 species of snake that reproduce solely through parthenogenesis (obligate parthenogenesis).Vitt, Laurie J., and Janalee P. Caldwell.
|
|
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.
|
|
Flies attracted to the moss carry its spores to fresh herbivore dung, which is the favoured habitat of the species of this genus. In many mosses, e.g., Ulota phyllantha, green vegetative structures called gemmae are produced on leaves or branches, which can break off and form new plants without the need to go through the cycle of fertilization. This is a means of asexual reproduction, and the genetically identical units can lead to the formation of clonal populations.
|
|
Liberation of gametes into the sea is linked to the phase of the moon and other factors. After fertilisation, the planula larvae form part of the plankton and eventually settle on the seabed and undergo metamorphosis into polyps. In some instances, M. auretenra has been observed to retain the gametes on its mesenteries and pseudo-brood the larvae briefly before liberating them into the sea. M. auretenra also reproduces readily by fragmentation, a form of asexual reproduction.
|
|
While inside the snail, the miracidia undergo several asexual reproduction and the larvae eventually become cercariae. The cercariae form exits the snail and is free swimming in water, in search for a fitting fish host. They burrow inside the fish or frog host, and the cercariae encyst and continue its next larval stage, known as "metacercariae", which are the yellow grubs. The grubs can live within the host for several years until eaten by a bird host.
|
|
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.
|
|
Carbon dating has found that these plants range from approximately 120–330 years of age and this research also found that populations are heavily skewed towards older plants, meaning there has been little or no replacement in these populations since the introduction of grazing animals in the 1860s. This however is not the only reason for small populations. The plant has an ancient history of asexual reproduction along with habitat disturbance which both have affected the setting of seed.
|
|
Many ascomycete species have only been observed undergoing asexual reproduction (called anamorphic species), but analysis of molecular data has often been able to identify their closest teleomorphs in the Ascomycota. Because the products of meiosis are retained within the sac-like ascus, ascomycetes have been used for elucidating principles of genetics and heredity (e.g., Neurospora crassa). Members of the Basidiomycota, commonly known as the club fungi or basidiomycetes, produce meiospores called basidiospores on club-like stalks called basidia.
|
|
Prasinococcus have a firm cell wall lacking scales and also lack flagella. The mitochondrial lobe and chloroplast outer membrane both protrude into the pyrenoid matrix which is considered characteristic of the genus. The cell wall has a protruding circular collar which is surrounded by holes which penetrate the cell wall. Its method of asexual reproduction is also considered characteristic - after cell division one daughter cell remains within the original cell wall while the other is extruded.
|
|
Blooms have been noted in contaminated environments due to excess augmentation of ammonia from industrial waste and are now being associated with the drop in biodiversity in such water bodies. Both sexual and asexual reproduction are possible for species within this genus. In addition, mitosis is well defined in Tetraspora species; particularly investigated in T. gelatinosa. Cell division involves elaborate arrangement of microtubules, basal body complexes and involve the use of structures like phycoplasts and protoplast.
|
|
In some crops, particularly apples, the rootstocks are vegetatively propagated so the entire graft can be clonal if the scion and rootstock are both clones. Apomixis (including apospory and diplospory) is a type of reproduction that does not involve fertilization. In flowering plants, unfertilized seeds are produced, or plantlets that grow instead of flowers. Hawkweed (Hieracium), dandelion (Taraxacum), some citrus (Citrus) and many grasses such as Kentucky bluegrass (Poa pratensis) all use this form of asexual reproduction.
|
|
Its primary nutrients are the sugars xylose, arabinose, glucose, sucrose, ribitol, xylitol and L-arabinitol. It cannot assimilate maltose or lactose; however, it is able to assimilate urea, asparagine, potassium nitrate and ammonium nitrate. The optimal temperature for growth is and the fungus is generally considered to be mesophilic, although it can grow at higher temperatures (up to ) as well. Asexual reproduction manifests in one of two forms: the Scedosporium type (the most common type) and the Graphium type.
|
|
Additionally, they have the ability to split into smaller colonies via asexual reproduction. X are capable of infecting other organisms and mimicking their prey's DNA and memories. They do this by infecting the organism's nervous system where they then start reproducing at an exponential rate, killing the host creature in the process. Once that is accomplished, the X absorb the DNA of their host and are then able to use it to mimic their prey perfectly.
|
|
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.
|
|
The life cycles of Schistosoma japonicum and Schistosoma mansoni are very similar. In brief, eggs of the parasite are released in the feces and if they come in contact with water they hatch into free-swimming larva, called miracidia. The larva then has to infect a snail of the genus Oncomelania such as species of Oncomelania hupensis within one or two days. Inside the snail, the larva undergo asexual reproduction through a series of stages called sporocysts.
|
|
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.
|
|
A colony starts when a larva settles on a suitable surface and undergoes metamorphosis into an ancestrula. This forms daughter zooids by budding and the colony grows by asexual reproduction. In common with other bryozoans, Electra pilosa filter feeds with the aid of a crown of tentacles known as a lophophore with which it sieves particles from the water. It probably feeds on such things as flagellates, phytoplankton, bacteria, small pieces of algal debris and algal spores.
|
|
Some liverworts are capable of asexual reproduction; in bryophytes in general "it would almost be true to say that vegetative reproduction is the rule and not the exception." For example, in Riccia, when the older parts of the forked thalli die, the younger tips become separate individuals. Some thallose liverworts such as Marchantia polymorpha and Lunularia cruciata produce small disc-shaped gemmae in shallow cups.Smith, AJE (1989) The Liverworts of Britain and Ireland, Cambridge University Press, Cambridge.
|
|
Aphids are among the most destructive insect pests on cultivated plants in temperate regions. In addition to weakening the plant by sucking sap, they act as vectors for plant viruses and disfigure ornamental plants with deposits of honeydew and the subsequent growth of sooty moulds. Because of their ability to rapidly increase in numbers by asexual reproduction and telescopic development, they are a highly successful group of organisms from an ecological standpoint. Control of aphids is not easy.
|
|
The yeast Saccharomyces cerevisiae reproducing by budding Some cells divide by budding (for example baker's yeast), resulting in a "mother" and a "daughter" cell that is initially smaller than the parent. Budding is also known on a multicellular level; an animal example is the hydra, which reproduces by budding. The buds grow into fully matured individuals which eventually break away from the parent organism. Internal budding is a process of asexual reproduction, favoured by parasites such as Toxoplasma gondii.
|
|
As bilaterians, platyhelminthes are triploblastic, but have no internal body cavity (are acoelomate), and lack specialized circulatory and respiratory organs, so gas exchange is by simple diffusion. This limits the thickness of the body, so they are either microscopic or are flat and ribbon- or leaf- shaped, and vulnerable to fluid loss. The body is filled with mesenchyme, a connective tissue that can regenerate injured tissues and permits asexual reproduction. The nervous system is concentrated at the head end.
|
|
Parthenogenesis is a form of asexual reproduction in which growth and development of embryos occur without fertilisation. Technically, parthenogenesis is not a behaviour, however, sexual behaviours may be involved. Whip-tailed lizard females have the ability to reproduce through parthenogenesis and as such males are rare and sexual breeding non-standard. Females engage in "pseudocopulation" to stimulate ovulation, with their behaviour following their hormonal cycles; during low levels of oestrogen, these (female) lizards engage in "masculine" sexual roles.
|
|
Tan and pink tipped variation The giant Caribbean sea anemone's primary mating season is reported to be in late May; however, they may continue to reproduce at a low levels throughout the year. This anemone is generally dioecious but occasionally hermaphroditic. It has a 1:1 to sex ratio (males to females) with no evidence of brooding or of asexual reproduction or division furrowing. The giant Caribbean sea anemone's reproduction scheme has been defined as oviparous → planktonic → lecithotrophic.
|
|
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).
|
|
Among bacteria, individual organisms are vulnerable and can easily die, but on the level of the colony, bacteria can live indefinitely. The two daughter bacteria resulting from cell division of a parent bacterium can be regarded as unique individuals or as members of a biologically "immortal" colony. The two daughter cells can be regarded as "rejuvenated" copies of the parent cell because damaged macromolecules have been split between the two cells and diluted. See asexual reproduction.
|
|
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.
|
|
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.
|
|
Astroides calycularis is a colonial coral, consisting of a group of polyps, each of which sits in a stony cup known as a calyx. The colonies are in diameter and high and each polyp is about in diameter. The polyps are yellow or orange, each with a fringe of about thirty very short tentacles surrounding a slit-shaped mouth. The colony grows by asexual reproduction, new polyps budding off existing polyps and secreting their own calices.
|
|
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.
|
|
Because the algae live in the vacuoles of the cells, they are protected from the digestive enzymes of the Hydra. During long period of darkness, such as storms or blooms that block sunlight, algae loss starts from the tentacles, hypostome and growth region. But when light conditions return the algae undergo a rapid multiplication and can repopulate the host in approximately two days. Chlorella undergo asexual reproduction which is in correlation with the division of the host.
|
|
In biology, the question of the individual is related to the definition of an organism, which is an important question in biology and philosophy of biology, despite there having been little work devoted explicitly to this question. An individual organism is not the only kind of individual that is considered as a "unit of selection". Genes, genomes, or groups may function as individual units. Asexual reproduction occurs in some colonial organisms so that the individuals are genetically identical.
|
|
A form of asexual reproduction related to parthenogenesis is gynogenesis. Here, offspring are produced by the same mechanism as in parthenogenesis, but with the requirement that the egg merely be stimulated by the presence of sperm in order to develop. However, the sperm cell does not contribute any genetic material to the offspring. Since gynogenetic species are all female, activation of their eggs requires mating with males of a closely related species for the needed stimulus.
|
|
There are a few ways that reproduction occurs within plant life, and one way is through parthenogenesis. Parthenogenesis is defined as "a form of asexual reproduction in which genetically identical offspring (clones) are produced". Another form of reproduction is through cross-fertilization, which is defined as "fertilization in which the egg and sperm are produced by different individuals", and in plants this occurs in the ovule. Once an ovule is fertilized within the plant this becomes what is known as a seed.
|
|
If created, a "female sperm" cell could fertilize an egg cell, a procedure that, among other potential applications, might enable female same-sex couples to produce a child who would be the biological offspring of their two mothers. It is also claimed that production of female sperm may stimulate a woman to be both the mother and father (similar to asexual reproduction) of an offspring produced by her own sperm. Many queries, both ethical and moral, arise over these arguments.
|
|
Many species go through schizogamy, where the atoke uses asexual reproduction to produce buds from its posterior end. Each bud develops into an epitoke and, once fully formed, will then break off from the atoke and become free-swimming. Many genetically identical epitokes are formed in this way, thus allowing a higher chance of finding a mate of the same species and subsequent passing of genes to the next generation. Atokes may then live through another season to form more epitokes.
|
|
Herland is a utopian novel from 1915, written by feminist Charlotte Perkins Gilman. The book describes an isolated society composed entirely of women, who reproduce via parthenogenesis (asexual reproduction). The result is an ideal social order: free of war, conflict, and domination. It was first published in monthly installments as a serial in 1915 in The Forerunner, a magazine edited and written by Gilman between 1909 and 1916, with its sequel, With Her in Ourland beginning immediately thereafter in the January 1916 issue.
|
|
There is no larval form and a single embryo develops in each individual in the aggregate. This later becomes detached from the aggregate and becomes a solitary individual ready to undergo asexual reproduction by budding again. The animal's rapid growth and this alternation of generations means that the population can build up rapidly when there is a plentiful food supply such as a bloom of phytoplankton. The salps themselves are eaten by fish, turtles, birds, jellyfish, heteropods, siphonophores and ctenophores.
|
|
In cell biology, ways in which fragmentation is useful for a cell: DNA cloning and apoptosis. DNA cloning is important in asexual reproduction or creation of identical DNA molecules, and can be performed spontaneously by the cell or intentionally by laboratory researchers. Apoptosis is the programmed destruction of cells, and the DNA molecules within them, and is a highly regulated process. These two ways in which fragmentation is used in cellular processes describe normal cellular functions and common laboratory procedures performed with cells.
|
|
DNA cloning can be performed spontaneously by the cell for reproductive purposes. This is a form of asexual reproduction where an organism splits into fragments and then each of these fragments develop into mature, fully grown individuals that are clones of the original organism (See reproductive fragmentation). DNA cloning can also be performed intentionally by laboratory researchers. Here, DNA fragmentation is a molecular genetic technique that permits researchers to use recombinant DNA technology to prepare large numbers of identical DNA molecules.
|
|
P. fusiformis has a full life cycle of approximately 5–7 days and reproduces asexually. The reproduction phase creates 1 or 2 zoospores which grow inside of the parent's cell wall until they become new cells. Observed in the laboratory under culture, asexual reproduction begins when the protoplast contracts away from the parental cell wall. In P. fusiformis, the protoplasm contracts near the middle of the cell forming two lobes, as opposed to Pyrocystis lunula, which forms crescent moon-like shapes while dividing.
|
|
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.
|
|
Saccharomyces cerevisiae reproducing by budding Budding is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. The small bulb-like projection coming out from the yeast cell is called a bud. Since the reproduction is asexual, the newly created organism is a clone and excepting mutations is genetically identical to the parent organism. Organisms such as hydra use regenerative cells for reproduction in the process of budding.
|
|
In hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and, when fully mature, detach from the parent body and become new independent individuals. Internal budding or endodyogeny is a process of asexual reproduction, favored by parasites such as Toxoplasma gondii. It involves an unusual process in which two daughter cells are produced inside a mother cell, which is then consumed by the offspring prior to their separation.
|
|
Sea urchins are constantly replacing spines lost through damage. Sea stars and sea lilies readily lose and regenerate their arms. In most cases, a single severed arm cannot grow into a new starfish in the absence of at least part of the disc.See last paragraph in review above Analysis However, in a few species a single arm can survive and develop into a complete individual and in some species, the arms are intentionally detached for the purpose of asexual reproduction.
|
|
Cloudina was originally classified in 1972 as a member of the Cribricyathea, a class known from the Early Cambrian. Glaessner (1976) accepted this classification and also proposed that Cloudina was similar to the annelid worms, particularly serpulid polychaetes. However, Hahn & Pflug (1985) and Conway Morris et al.. (1990) doubted both Germs' and Glaessner's suggested relationships, and were unwilling to classify it to anything more than its own family, Cloudinidae. Some specimens of Cloudina hartmannae display budding, which implies asexual reproduction.
|
|
These in turn undergo further asexual reproduction, ultimately yielding large numbers of the second free-living stage, the cercaria (pl. cercariae). Free-swimming cercariae leave the snail host and move through the aquatic or marine environment, often using a whip- like tail, though a tremendous diversity of tail morphology is seen. Cercariae are infective to the second host in the life cycle, and infection may occur passively (e.g., a fish consumes a cercaria) or actively (the cercaria penetrates the fish).
|
|
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.
|
|
When the fungus germinates, it produces different kinds of esterases, including cutinase, which help the fungus to penetrate the plant cell wall. The disease can also affect other adjacent healthy fruits when distributed by wind or insect activity. Some species of Syncephalis can reduce the asexual reproduction of R. stolonifer and therefore may delay or even prevent the post-harvest disease caused by this fungus. Fengycin, which is an anti-fungal complex, also induces the fungal cell death via necrosis and apoptosis.
|
|
Reproducing sexually allows the species to disperse to new locations in a way it could not do if it relied entirely on asexual reproduction. The lifespan is at least four years. During its second and third years, when it is actively growing and its arm length is either about 15 or 22 mm, N. belcheri can reproduce by fragmentation. A furrow appears on the disc which gradually deepens, and the two sides of the starfish pull away from each other.
|
|
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.
|
|
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.
|
|
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.
|
|
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.
|
|
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.
|
|
They can reproduce both sexually and asexually, though asexual reproduction is much more common and occurs through a process called fragmentation. Although Elkhorn coral dominated the Caribbean in the early 1980s, the species has since dramatically declined in numbers. Scientists have estimated that between 1980 and 2006, when it was listed in the Endangered Species Act (ESA), the population declined by around 97%. This decline was due to a variety of factors, including disease, algae growth, climate change, ocean acidification, and human activity.
|
|
After the asexual reproduction stage cercaria (another free-swimming larva) are generated in large quantities, which then leave (shed into the environment) the snail and must infect a suitable vertebrate host. Once the cercaria penetrates the skin of the host it loses its tail and becomes a schistosomule. The worms then migrate through the circulation ending at the mesenteric veins where they mate and start laying eggs. Each pair deposits around 1500-3500 eggs per day in the vessels of the intestinal wall.
|
|
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.
|
|
The name comes from the Greek word for dust, κόνις kónis.Conidium in the Collins Dictionary They are also called mitospores due to the way they are generated through the cellular process of mitosis. The two new haploid cells are genetically identical to the haploid parent, and can develop into new organisms if conditions are favorable, and serve in biological dispersal. Asexual reproduction in ascomycetes (the phylum Ascomycota) is by the formation of conidia, which are borne on specialized stalks called conidiophores.
|
|
Cladosporium sphaerospermum is a radiotrophic fungus belonging to the genus Cladosporium and was described in 1886 by Albert Julius Otto Penzig from the decaying leaves and branches of Citrus. It is a dematiaceous (darkly- pigmented) fungus characterized by slow growth and largely asexual reproduction. Cladosporium sphaerospermum consists of a complex of poorly morphologically differentiated, "cryptic" species that share many physiological and ecological attributes. In older literature, all of these sibling species were classified as C. sphaerospermum despite their unique nature.
|
|
Another form of asexual reproduction takes place, possibly in response to stress, when gemmules form as rounded stubby outgrowths from the branches. These become detached and float away and, being adhesive, stick to objects they may encounter and found a new colony. Experimentally, gemmule production has been triggered by a sudden change in temperature of 5 °C (9 °F), lack of aeration of the water or an over-abundance of food. Each colony of Obelia longissima is either male or female.
|
|
Gene conversion - the process during which homologous sequences are made identical also falls under genetic recombination. Genetic recombination and recombinational DNA repair also occurs in bacteria and archaea, which use asexual reproduction. Recombination can be artificially induced in laboratory (in vitro) settings, producing recombinant DNA for purposes including vaccine development. V(D)J recombination in organisms with an adaptive immune system is a type of site- specific genetic recombination that helps immune cells rapidly diversify to recognize and adapt to new pathogens.
|
|
L. janetae has 8 gonads which are shaped like lances and arranged in pairs extending from the centre of the calyx to the base of the arms. They give the organism an orange/pink colour when reproductively active. The scientists who originally identified L. janetae have speculated that this species may also be capable of asexual reproduction. This had not been shown for any Stauromedusan at the time the paper was written, although it has subsequently been suggested for Haliclystus antarcticus.
|
|
Each flower is white with bright yellow-pink anthers. The plant produces capsules of abundant seeds but also reproduces vegetatively. When it does reproduce sexually, it often self-pollinates. Bensoniella is not endangered but it is a species of some concern for several reasons, including lack of genetic diversity in part due to its habit of self-pollination and asexual reproduction, its relatively narrow tolerance of habitats, its small range of distribution, habitat destruction due to logging, grazing, and road- building, and erosion.
|
|
Sanderia malayensis has a complex life cycle with a number of types of asexual reproduction. New polyps can bud off existing polyps, with a moveable stolon developing at the same time on the opposite side of the mother polyp. These stolons may develop a knobbed end, curl up and attach themselves to the substrate, before detaching from the mother polyp and developing into a new polyp. Strobilation of the polyp may occur with ephyrae being formed which separate from the mother polyp.
|
|
Fragmentation in multicellular organisms is a form of asexual reproduction in which an organism is split into fragments. Each of these fragments develop into matured organism, full grown individuals that are genetically and morphologically identical to their parents. The splitting may or may not be intentional – it may or may not occur due to man-made or natural damage by the environment or predators. This kind of organism may develop specific organs or zones that may be shed or easily broken off.
|
|
The yeast cell's life cycle: Yeasts, like all fungi, may have asexual and sexual reproductive cycles. The most common mode of vegetative growth in yeast is asexual reproduction by budding, where a small bud (also known as a bleb or daughter cell) is formed on the parent cell. The nucleus of the parent cell splits into a daughter nucleus and migrates into the daughter cell. The bud then continues to grow until it separates from the parent cell, forming a new cell.
|
|
Bdelloids are of interest in the study of the evolution of sex because a male has never been observed, and females reproduce exclusively by parthenogenesis, a form of asexual reproduction where embryos grow and develop without the need for fertilization; this is akin to the apomixis seen in some plants. Each individual has paired gonads. Despite having been asexual for millions of years, they have diversified into more than 450 species and are fairly similar to other sexually reproducing rotifer species.
|
|
The rotifers that were consistently kept hydrated fared worse than those desiccated and rehydrated. Bdelloidea have evolved a unique mechanism to help overcome one of the major perils of asexual reproduction. According to the Red Queen hypothesis of co-evolution, obligate asexuals will be driven extinct by rapidly changing parasites and pathogens, because they cannot change their genotypes quickly enough to keep up in this never-ending race. In populations of bdelloid rotifers, however, many parasites are destroyed during periods of extended desiccation.
|
|
Haemoproteus ilanpapernai The infective stage is the sporozoite which is present in the salivary glands of the vector. Once the vector bites a new host, the sporozoites enter the blood stream and invade endothelial cells of blood vessels within various tissues including those of the lung, liver and spleen. Within the endothelial cells, the sporozoites undergo asexual reproduction becoming schizonts. These in turn produce numerous merozoites which penetrate the erythrocytes and mature into either female gametocytes (macrogametocytes) or male gametocytes (microgametocytes).
|
|
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.
|
|
L. guildingi sometimes exhibits autotomy, shedding one or more of its arms. In a study on Hawaii, it was found that autotomy happens less frequently than in the related species, Linckia multifora, also found in these waters. In time the arm will regenerate and in both species, the detached arms, known as "comets", are capable of moving about independently and themselves developing into new individuals, a form of asexual reproduction. The process is quite slow, it taking 6 months for the madreporite to appear.
|
|
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.
|
|
Mosses belonging to the class of Polytrichopsida are known for several defining characteristics such as stem leaves with unistratose lamina, numerous lamellae, a costa, stereids, guide cells, and hydroids. Polytrichopsida mosses also have a strong conducting strand composed of hydroids (water conduction) and leptoids (conduction of sugar and other nutrients), leaf traces, and stereids. Due to the lack of gemmae producing structures in the majority of mosses that belong to this class, Polytrichopsida mosses reproduce sexually by spore dispersal. However, asexual reproduction by fragmentation is possible.
|
|
Polymorphism refers to the occurrence of structurally and functionally more than two different types of individuals within the same organism. It is a characteristic feature of Cnidarians, particularly the polyp and medusa forms, or of zooids within colonial organisms like those in Hydrozoa. In Hydrozoans, colonial individuals arising from individuals zooids will take on separate tasks. For example, in Obelia there are feeding individuals, the gastrozooids; the individuals capable of asexual reproduction only, the gonozooids, blastostyles and free-living or sexually reproducing individuals, the medusae.
|
|
In the 1930s, water hyacinth was introduced into China as a feed, ornamental plant and sewage control plant, and it was widely planted in the south as an animal feed. Beginning in the 1980s, with the rapid development of China's inland industry, the eutrophication of inland waters has intensified. With the help of its efficient asexual reproduction and environmental adaptation mechanisms, water hyacinth has begun to spread widely in the river basin. The flood-water blue eyes blocked the river and hindered the internal water traffic.
|
|
The productive life of the plants can extend to up to eight decades, with two fruit harvests per year. The successful conservation of the Agraz requires familiarity with its reproductive biology. This is a clonal plant that produces genetically identical individuals through vegetative reproduction, whose genetic structure is complex, with a mix of plants that arise from sexual and asexual reproduction; it is therefore advisable, in addition to field collection, to keep the seeds of a few plants, for a greater representation of genetic variability.
|
|
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.
|
|
However, in karyorelicteans, the macronuclei are unable to divide. Instead, they must be produced by division and differentiation of a micronucleus every time, even during asexual reproduction. Because of their non-dividing somatic macronuclei, the karyorelicteans were thought to represent an intermediate evolutionary stage between the hypothetical ancestor of ciliates that did not have nuclear dualism, and the other more "advanced" ciliates which had both nuclear dualism and macronuclei that could divide by amitosis. The name of the group therefore makes reference to their supposedly "primitive" nuclei.
|
|
During asexual reproduction of Astrephomene, rotation of daughter protoplasts occurs in conjunction with the movement of basal bodies during successive cell divisions, ending with the anterior end of all cells of the daughter colony outside after the first nuclear and cytoplasmic division.Yamashita S, Arakaki Y, Kawai-Toyooka H, Noga A, Hirono M, Nozaki H. Alternative evolution of a spheroidal colony in volvocine algae: developmentalanalysis of embryogenesis in Astrephomene (Volvocales, Chlorophyta). BMC Evol Biol. 2016 Nov 9;16(1):243. PubMed PMID: 27829356; PubMed Central PMCID: PMC5103382.
|
|
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.
|
|
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.
|
|
Meristem tissue makes the process of asexual reproduction possible. It is normally found in stems, leaves, and tips of stems and roots and consists of undifferentiated cells that are constantly dividing allowing for plant growth and give rise to plant tissue systems. The meristem tissue's ability to continuously divide allows for vegetative propagation to occur. Another important ability that allows for vegetative propagation is the ability to develop adventitious roots which arise from other vegetative parts of the plants such as the stem or leaves.
|
|
Inset shows the surrounding, black poplars growing on sandy loam on the bank of a kolk, with the detail area marked. In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, fungi and protozoa. Bacterial spores are not part of a sexual cycle but are resistant structures used for survival under unfavourable conditions.
|
|
A study estimated that one group of colonies in a patch measuring produced 800,000 statoblasts. Cupuladriid Bryozoa are capable of both sexual and asexual reproduction. The sexually reproducing colonies (aclonal) are the result of a larval cupuladriid growing into an adult stage whereas the asexual colonies(clonal) are a result of a fragment of a colony of cupuladriids growing into its own colony. The different forms of reproduction in cupuladriids are achieved through a variety of methods depending on the morphology and classification of the zooid.
|
|
The primary mating systems in plants are outcrossing (cross-fertilisation), autogamy (self-fertilisation) and apomixis (asexual reproduction without fertilization, but only when arising by modification of sexual function). Mixed mating systems, in which plants use two or even all three mating systems, are not uncommon. A number of models have been used to describe the parameters of plant mating systems. The basic model is the mixed mating model, which is based on the assumption that every fertilisation is either self-fertilisation or completely random cross-fertilisation.
|
|
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.
|
|
Aquatic plants are phylogenetically well dispersed across the angiosperms, with at least 50 independent origins, although they comprise less than 2% of the angiosperm species. Archefructus represents one of the oldest, most complete angiosperm fossils which is around 125 million years old. These plants require special adaptations for living submerged in water or floating at the surface. Although most aquatic plants can reproduce by flowering and setting seeds, many have also evolved to have extensive asexual reproduction by means of rhizomes, turions, and fragments in general.
|
|
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.
|
|
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.
|
|
Further asexual reproduction takes place, with each zooid producing several buds until there is a small, roughly circular encrusting cluster of zooids, white or brownish-white in colour, with the ancestrula at the centre. On flat surfaces the colony is regular and lacy in appearance but on uneven surfaces, it is more irregular and may form lobes. Some colonies are also spherical. Each individual zooid bears a lophophore, the characteristic feeding apparatus of bryozoans, with fifteen or sixteen ciliated tentacles, used to filter phytoplankton.
|
|
Brooding anemone (Epiactis prolifera) with developing young Unlike other cnidarians, anemones (and other anthozoans) entirely lack the free-swimming medusal stage of their lifecycle; the polyp produces eggs and sperm, and the fertilized egg develops into a planula larva which develops directly into another polyp. Both sexual and asexual reproduction can occur. The sexes in sea anemones are separate in some species, while other species are sequential hermaphrodites, changing sex at some stage in their life. The gonads are strips of tissue within the mesenteries.
|
|
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.
|
|
Eggs shed in water release free-swimming larval forms that are infective to the intermediate host, in which asexual reproduction occurs. A species that exemplifies the remarkable life history of the trematodes is the bird fluke, Leucochloridium paradoxum. The definitive hosts, in which the parasite reproduces, are various woodland birds, while the hosts in which the parasite multiplies (intermediate host) are various species of snail. The adult parasite in the bird's gut produces eggs and these eventually end up on the ground in the bird's faeces.
|
|
Some studies suggest that populations of D. pulicaria in lakes in North America reproduce using the expected pattern of cyclic parthenogenesis while other populations in smaller ponds have shifted toward obligate parthenogenesis. The number of offspring produced through asexual reproduction is heavily influenced by the environmental conditions experienced by an individual. For instance, females in a high-food environment with a longer photoperiod tend to have more offspring. Environmental cues, such as food level, photoperiod, and temperature, significantly influence the reproduction of D. pulicaria.
|
|
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.
|
|
A Calamites rhizoid Calamites reproduced by means of spores, which were produced in small sacs organized into cones. They are also known to have possessed massive underground rhizomes, which allowed for the production of clones of one tree. This is the only group of trees of their period known to have a clonal habit. This type of asexual reproduction would allow them to spread quickly into new territory, and help to anchor them firmly in the unstable ground along rivers and in newly deposited delta sediments.
|
|
An unusual aspect of P. surinamensis is that the species reproduces parthenogenetically, a form of asexual reproduction in which embryos develop from unfertilized eggs. P. surinamensis reproduce by thelytokous parthenogenesis, a type of parthenogenesis in which offspring are almost exclusively female clones. Thelytokous parthenesis is known in about 1% of known animal species. Optional thelkytokous parthenogenesis occurs in several cockroach species when females are isolated from males, including in the common domestic pests Blatta orientalis, Blattella germanica, and Periplaneta americana, but in P. surinamensis it is obligatory parthenogenesis, its sole means of reproduction.
|
|
The basidia (spore-bearing cells) are ellipsoid to roughly spherical in shape, not or rarely stalked, and typically 15–21 µm wide. They contain two to four septa that divide it into compartments; the septa are most frequently diagonal or vertical. Asexual reproduction in T. mesenterica is carried out through the formation of spores called conidia, which arise from conidiophores—specialized hyphal cells that are morphologically distinct from the somatic hyphae. The conidiophores are densely branched and normally abundant in the hymenium; young specimens may be entirely conidial.
|
|
Colochirus robustus, commonly known as the robust sea cucumber or the yellow sea cucumber, is a species of sea cucumber in the family Cucumariidae. It is found in shallow seas in tropical parts of the central Indo-Pacific region. C. robustus belongs to the class Holothuroidea, a group of echinoderms called sea cucumbers and known for unusual behavior including evisceration, asexual reproduction, and regeneration. The robust sea cucumber has a soft body and lacks a spine, but it does have an endoskeleton consisting of microscopic spicules, or ossicles, made of calcium carbonate.
|
|
Allorecognition phenomena have been recognized in bacterial self-identity and social recognition systems, kin discrimination in social amoebae, fungal mating types, fungal vegetative incompatibility, plant self-incompatibility systems, colonial marine invertebrates (such as corals, sponges, hydroids, bryozoans, and ascidians), and of course, vertebrates. The manner in which allorecognition manifests itself in these different systems varies greatly. Bacteria, for instance, secrete bacteriocins, proteinaceous toxins specifically targeted against members of their own species. Colonies of marine invertebrates, each representing a single genotype, expand across the ocean floor by asexual reproduction.
|
|
Seagrasses are flowering species, but they can reproduce both sexually and asexually. Reproducing sexually increases genetic variation, which can enhance a plant's ability to adapt to a changing environment, but asexual reproduction requires less effort and is what Z. muelleri typically uses to maintain its population. When reproducing sexually, the plant's flowers form an inflorescence that is enclosed in a spathe (a large sheathing bract that encloses flower clusters in certain plant species). Each shoot can have up to 6 spathes, which contain 4-12 pairs of male and female flowers.
|
|
Gynogenesis, a form of parthenogenesis, is a system of asexual reproduction that requires the presence of sperm without the actual contribution of its DNA for completion. The paternal DNA dissolves or is destroyed before it can fuse with the eggEncyclopedia of Insects, edited by Vincent H. Resh, et al., Elsevier Science & Technology, 2009. . The egg cell of the organism is able to develop, unfertilized, into an adult using only maternal genetic material. Gynogenesis is often termed “sperm parasitism” in reference to the somewhat pointless role of male gametes.
|
|
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.
|
|
Unusually, the male gonopore opens on the dorsal surface of the animal, above the pharynx, while the female reproductive system lacks any of the usual ducts and related structures found in other flatworms. The sperm is nonmobile and lacks flagella or cilia. Asexual reproduction by paratomy is common, and it usually leads to a chain of organisms (zooids), hence the name, from Latin catenula, small chain. Members of the symbiotic genus Paracatenula lack a digestive tract, and instead harbor intracellular chemoautotrophic bacterial symbionts that are assumed to provide their nutrition.
|
|
Many colonial sea squirts are also capable of asexual reproduction, although the means of doing so are highly variable between different families. In the simplest forms, the members of the colony are linked only by rootlike projections from their undersides known as stolons. Buds containing food storage cells can develop within the stolons and, when sufficiently separated from the 'parent', may grow into a new adult individual. In other species, the postabdomen can elongate and break up into a string of separate buds, which can eventually form a new colony.
|
|
Metarhizium anisopliae, formerly known as Entomophthora anisopliae (basionym), is a fungus that grows naturally in soils throughout the world and causes disease in various insects by acting as a parasitoid. Ilya I. Mechnikov named it after the insect species from which it was originally isolated – the beetle Anisoplia austriaca. It is a mitosporic fungus with asexual reproduction, which was formerly classified in the form class Hyphomycetes of the phylum Deuteromycota (also often called Fungi Imperfecti). According to Paul Stamets, it could be the answer to prevent colony collapse disorder and catastrophic famine.
|
|
E. lineata has a simple internal structure and is unusual among sea anemones in that it can divide by transverse fission. This type of asexual reproduction can be achieved through either physal pinching or polarity reversal. In physal pinching, a constriction occurs at the aboral (physal) end of the anemone and the fragment then "pinches" off, at which point the fragment regenerates to form a fully functional adult polyp. During polarity reversal, oral structures form at the aboral end of the anemone resulting in an animal with two oral ends.
|
|
This ribbon worm is a detritivore and grazer. It is rather fragile, and any attempt to collect it is likely to end with the worm breaking in pieces. However, it is able to regenerate itself from any fragment that is at least half as long as the worm's diameter; each piece can develop into a complete new worm in three to four weeks. In fact this appears to be a form of asexual reproduction, the worm dividing along pre-arranged fracture lines; tiny pieces may form cysts, with the new worms developing inside these.
|
|
During an infestation there are usually 3 to 6 galls per leaf, but up to 65 have been observed on a single leaf. The adult wasps emerge from the galls after growing inside for 3–4 months. In temperate areas there may be 2-3 generations of adults in a year but in the tropics there can be as many as 6 generations. The females can reproduce asexually by thelytokous reproduction and live for up to 7 days, males are rare and the asexual reproduction allows L. invasa to rapidly increase its population size.
|
|
The embryos have yolks from which they derive nourishment while they are brooded inside the colonial tunic. When they hatch, after about two weeks, the larvae have a short free-living stage lasting up to a few hours, before undergoing metamorphosis into a zooid ready to found a new colony. The new colony grows by asexual reproduction, with new zooids budding off existing ones. A fragment of a colony may become detached (perhaps by "dripping" off a floating structure), adhere to a new substrate and found a new colony.
|
|
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.
|
|
Step labeled number 4 indicates karyogamy's place in the context of the life cycle of the fungus Taphrina. Haploid organisms such as fungi, yeast, and algae can have complex cell cycles, in which the choice between sexual or asexual reproduction is fluid, and often influenced by the environment. Some organisms, in addition to their usual haploid state, can also exist as diploid for a short time, allowing genetic recombination to occur. Karyogamy can occur within either mode of reproduction: during the sexual cycle or in somatic (non-reproductive) cells.
|
|
Individual colonies grow by asexual reproduction of polyps. Corals also breed sexually by spawning: polyps of the same species release gametes simultaneously overnight, often around a full moon. Fertilized eggs form planulae, a mobile early form of the coral polyp which when mature settles to form a new colony. Although some corals are able to catch plankton and small fish using stinging cells on their tentacles, most corals obtain the majority of their energy and nutrients from photosynthetic unicellular dinoflagellates of the genus Symbiodinium that live within their tissues.
|
|
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.
|
|
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.
|
|
Although K.E. Hirn was the first to publish concerning Odeogoniales, it is not clear as to whether he was the first to discover this new genus. First named Oedogoniaceen (German), Hirn used his knowledge of the Latin language to describe and name the green algal genus; oedos meaning swelling/tumor, and gonos meaning offspring/seed. This name was meant to describe the morphology during sexual and asexual reproduction which he saw and described within his publication, “Monographie und iconographie der Oedogoniaceen”. Hirn, K.E. 1900: Monographie und iconographie der Oedogoniaceen.
|
|
A = Branched morphotype with pseudotentacles (arrows show vesicles) B = Smooth disc morphotype There are a range of different morphotypes of this sea anemone. Some are smooth discs, some are similar to branching corals and others to dead coral rock covered by algae, resembling these models not only in shape, but also in colour. Some individuals are solitary and others form aggregations of similar morphotypes. The aggregations include a range of different-sized individuals and are likely to be clones formed by asexual reproduction, possibly by fragmentation when the sea anemone moves across the substrate.
|
|
Botryllus schlosseri is used as a model organism. Clones have been maintained in continuous laboratory culture for several decades, with new adults developing from buds that form from the body wall of existing adults. Under typical culture conditions, asexual reproduction occurs on an approximately two week cycle, during which a new bud will grow and begin to actively feed, while the adult it emerged from regresses and is eventually re-absorbed. When sexually productive, these Botryllus are known to produce,"yellowish-white or pale orange tadpole larva" exhibiting an oval outline.
|
|
Bryophyllum daigremontianum (Kalanchoe daigremontiana) Vegetative propagation is a type of asexual reproduction found in plants where new individuals are formed without the production of seeds or spores and thus without syngamy or meiosis. Examples of vegetative reproduction include the formation of miniaturized plants called plantlets on specialized leaves, for example in kalanchoe (Bryophyllum daigremontianum) and many produce new plants from rhizomes or stolon (for example in strawberry). Other plants reproduce by forming bulbs or tubers (for example tulip bulbs and Dahlia tubers). Some plants produce adventitious shoots and may form a clonal colony.
|
|
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.
|
|
Bdelloid rotifers reproduce exclusively asexually, and all individuals in the class Bdelloidea are females. Asexuality evolved in these animals millions of years ago and has persisted since. There is evidence to suggest that asexual reproduction has allowed the animals to evolve new proteins through the Meselson effect that have allowed them to survive better in periods of dehydration. Molecular evidence strongly suggests that several species of the stick insect genus Timema have used only asexual (parthenogenetic) reproduction for millions of years, the longest period known for any insect.
|
|
Ronald Fisher also suggested that sex might facilitate the spread of advantageous genes by allowing them to better escape their genetic surroundings, if they should arise on a chromosome with deleterious genes. Supporters of these theories respond to the balance argument that the individuals produced by sexual and asexual reproduction may differ in other respects too – which may influence the persistence of sexuality. For example, in the heterogamous water fleas of the genus Cladocera, sexual offspring form eggs which are better able to survive the winter versus those the fleas produce asexually.
|
|
These secondary, replicative spores are globose and elongate in physiology. Once the spore has been discharged, all subsequent developmental events are triggered, including germination. Sporangial germination, either through secondary spore formation or vegetative germ tube formation, seems to be increasingly dependent on the time elapsed since discharge, rather than on the external environmental factors, however these external factors do still play a role. The spores formed by C. coronatus during asexual reproduction are globose, villose and multiplicative in some isolates, and have at least seven nuclei per spore.
|
|
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.
|
|
The eyes of certain cavefish and salamanders are vestigial, as they no longer allow the organism to see, and are remnants of their ancestors' functional eyes. Animals that reproduce without sex (via asexual reproduction) generally lose their sexual traits, such as the ability to locate/recognize the opposite sex and copulation behavior.CJ van der Kooi & T Schwander 2014. On the fate of sexual traits under asexuality Biological Reviews 89:805-819 Boas and pythons have vestigial pelvis remnants, which are externally visible as two small pelvic spurs on each side of the cloaca.
|
|
In 2003, the mode of asexual reproduction in the bdelloid rotifers was wholly unknown. One theory of how obligate parthenogenesis arose in bdelloid rotifers was that parthenogenic lineages lost the ability to respond to sex-inducing signal, which is why these lineages retained their asexuality. The obligate parthenogenetic strains of bdelloid rotifers produce a sex-inducing signal but have lost the ability to respond to that signal. It was later discovered that the inability to respond to sex-inducing signals in obligate parthenogens was caused by simple Mendelian inheritance of the gene op.
|
|
Embryonated Microphallus eggs are ingested from sediment and hatch in the snail's gut, penetrate the intestine, and migrate to the gonads and digestive gland. Following successful establishment, the parasite then undergoes asexual reproduction, replacing much of the host's reproductive tissue and digestive gland, which results in complete sterilization of the snail. The first visible parasite developmental stages (blastocercariae) are detectable after approximately 75 days post- exposure and metacercariae are common by 90 days post-exposure at 16 °C in the lab. The life cycle is completed when snails containing metacercariae are consumed by waterfowl.
|
|
Metarhizium brunneum, is the re-instated name of a group of reassigned Metarhizium isolates, previously grouped in the species "Metarhizium anisopliae var. anisopliae": based on a multigene phylogenetic approach using near-complete sequences from nuclear DNA. It is a mitosporic fungus with asexual reproduction, which was formerly classified in the form class Hyphomycetes of the form phylum Deuteromycota (also often called Fungi Imperfecti). M. brunneum has been isolated from Coleoptera, Lepidoptera, Diptera and soil samples, but a commercially developed isolate (below) has proved virulent against Hemiptera and Thysanoptera.
|
|
Flowers appear on pineapple grass in summer on structures called racemes. The plant is dioecious, meaning it has separate male and female flowers. Like other species of Astelia, which grow in areas that are moist and humid, the ovary is full of mucilage, which is thought to function in pollen transmittance.Kocyan, A. and Endress, P.K. (2001) "Floral structure and development and systematic aspects of some 'lower' Asparagales" Plant Systematics and Evolution 229(3-4): 187-216 Humans can facilitate asexual reproduction by breaking apart mature clumps and planting them separately.
|
|
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.
|
|
A list of the known unisexual vertebrates, pp. 19-23 in: Evolution and Ecology of Unisexual Vertebrates. R.M. Dawley and J.P. Bogart (eds.) Bulletin 466, New York State Museum, Albany, New York Other usually sexual species may occasionally reproduce parthenogenetically; the Komodo dragon and hammerhead and blacktip sharks are recent additions to the known list of spontaneous parthenogenetic vertebrates. As with all types of asexual reproduction, there are both costs (low genetic diversity and therefore susceptibility to adverse mutations that might occur) and benefits (reproduction without the need for a male) associated with parthenogenesis.
|
|
Riitta Johanna Mappes (born 13 October 1965 in Valkeakoski, Finland) is a Finnish evolutionary ecologist. In her research, Mappes focuses on interspecific interactions, especially the evolution of warning signals and mimicry in chemically defended prey, as well as on the evolution of bacterial virulence and the evolution of sexual and asexual reproduction. In 2003 The Academy of Finland awarded Mappes the 'Young Dynamic Researcher Award' for her research merits, especially for developing and using the ‘novel world method’ in studying the evolution of aposematism. Mappes earned her MSc degree in 1991 and her PhD in 1994 from the University of Jyväskylä, Finland.
|
|
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.
|
|
Asexual reproduction may proceed along two different routes: 1) the entire content of the cell divides into elongated, uninucleate spores (known as sporangiospores or endospores) with the cell wall breaking apart to release the spores or 2) the entire content of the cell divides to produce teardrop-shaped, motile amoeboid cells that disperse for a short time, then encyst and produce spores from the cyst (called cystospores).Lichtenstein, J. L. 1917a. Sur un Amoebidium a commensalisme interne du rectum des larves d' Anax imperator Leach: Amoebidium fasciculatum n. sp. Archives de Zoologie Expérimentale et Générale 56: 49-62.
|
|
These may be genetic, related to the genomes, or the interaction between nuclear and cytoplasmic factors, as will be discussed in the corresponding section. Nevertheless, it is important to note that in plants, hybridization is a stimulus for the creation of new species – the contrary to the situation in animals. Although the hybrid may be sterile, it can continue to multiply in the wild by asexual reproduction, whether vegetative propagation or apomixis or the production of seeds. Indeed, interspecific hybridization can be associated with polyploidia and, in this way, the origin of new species that are called allopolyploids.
|
|
The large, multinucleate foraminferan is characteristic for its lack of test and named for the network of connecting pseudopodia surrounding its central body mass. The organism has unique bidirectional cytoplasmic streaming throughout the anastomosing pseudopodia that is some of the fastest reported organelle transport observed. Reticulomyxa was first described in 1949 and is commonly used as a model organism for the unique transport of organelles throughout the cytoplasm of pseudopodia by cytoskeletal mechanisms. Only asexual reproduction of this genus has been observed in culture, but the genome possesses genes related to meiosis suggesting it is capable of sexually reproductive life stages.
|
|
Some brittle stars, such as the six-armed members of the family Ophiactidae, exhibit fissiparity (division through fission), with the disk splitting in half. Regrowth of both the lost part of the disk and the arms occur which yields an animal with three large arms and three small arms during the period of growth. The West Indian brittle star, Ophiocomella ophiactoides, frequently undergoes asexual reproduction by fission of the disk with subsequent regeneration of the arms. In both summer and winter, large numbers of individuals with three long arms and three short arms can be found.
|
|
Through her genesis based attributes Lilith can literally give birth to countless races beyond those of the demonic lilim; ranging from humans to mutants and mystical beasts, etc.Marvel Appendix She can just as easily revitalize any of her fallen brood through the act of rebirthing any when after they die. She does so either through natural copulative procreation, consuming prior offspring, conjuring them out of nothingness, conversion of other species or through asexual reproduction. Her power also enables her to transmigrate living souls consumed into new entities, respawning them as any given species she desires at a later date in time.
|
|
Even such massive corals as Montastraea annularis have been shown to be capable of forming new colonies after fragmentation. This process is used in the reef aquarium hobby to increase stock without the necessity to harvest corals from the wild. Under adverse conditions, certain species of coral resort to another type of asexual reproduction in the form of "polyp bail-out", which may allow polyps to survive even though the parent colony dies. It involves the growth of the coenosarc to seal off the polyps, detachment of the polyps and their settlement on the seabed to initiate new colonies.
|
|
Sexual maturity is reached at a length of around and an age of 8-9 years, though mature males as small as long have been recorded from the Maldives, suggesting regional variation in maturation size. On the Great Barrier Reef, males live to 14 years and females to 19 years; the maximum lifespan of this shark may be upwards of 25 years. In 2008, a whitetip reef shark produced a single pup through possibly asexual means at the Nyiregyhaza Centre in Hungary; previous instances of asexual reproduction in sharks have been reported in the bonnethead (Sphyrna tiburo) and the blacktip shark (Carcharhinus limbatus).
|
|
Some species in this genus used to live in areas of white water in the Yacyretá Rapids, Paraná River, feeding on the algae that grow attached to the rocks on the bottom. The water in the area is saturated with oxygen, from the fast-moving waters. Aylacostoma is a parthenogenic species: the population consists of only females, which increase in number by asexual reproduction. The females give birth to a small number of larvae, no more than three, that are born very well developed, so they have the physical strength needed to attach to a rock and resist the strong current.
|
|
Realistic models for human societies ask for a bisexual mode of reproduction whereas in the definition of an RDBP one simply speaks of a law of reproduction. However the notion of an average reproduction rate per individual (Bruss 1984) for bisexual processes shows that for all relevant questions for the long-term behavior of human societies it is justified for simplicity to assume asexual reproduction. This is why certain limiting results of Klebaner (1984) and Jagers & Klebaner (2000) bear over to RDBPs. Models for the development of a human society in time must allow for interdependence between the different components.
|
|
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 majority of female scale insects remain in one place as adults, with newly hatched nymphs, known as "crawlers", being the only mobile life stage, apart from the short-lived males. The reproductive strategies of many species include at least some amount of asexual reproduction by parthenogenesis. Some scale insects are serious commercial pests, notably the cottony cushion scale (Icerya purchasi) on Citrus fruit trees; they are difficult to control as the scale and waxy covering protect them effectively from contact insecticides. Some species are used for biological control of pest plants such as the prickly pear, Opuntia.
|
|
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.
|
|
Acorn worms are dioecious, having separate biological sexes, although at least some species are also capable of asexual reproduction. They have paired gonads, which lie close to the pharynx and release the gametes through a small pore near to the gill slits. The female lays a large number of eggs embedded in a gelatinous mass of mucus, which are then externally fertilized by the male before water currents break up the mass and disperse the individual eggs. Acorn worm life cycle by M. Singh In most species, the eggs hatch into planktonic larvae with elongated bodies covered in cilia.
|
|
The Guardians of the Universe, fearing the ruthlessly and violently powerful Martians, genetically split the Martian race into two distinct species, white and green, preventing the asexual reproduction. They also gave these two new races an instinctive fear of fire to prevent either group from ever accessing their full potential, and altered their powers so one race could never completely overcome the other. The timeframe for this genetic tampering was given as 20,000 years ago, contemporary with the early life of Vandal Savage on Earth, in JLA series 2 #86. While the Green Martians were peaceful philosophers, the White Martians were savage warriors.
|
|
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.
|
|
This seaweed reproduces by spore- producing asexual reproduction. The fronds produce tetraspores in concentric bands a millimetre () or so wide, alternately on the upper and lower surfaces of the fronds, closely situated between bands of hairs. The sporangia within the sori mature at differing rates, so that the mature sorus contains spores at very different stages of development. The species has been investigated for use as a bioindicator of heavy metal contamination; it concentrated iron and manganese by several orders of magnitude and was also successful in detecting other metals such as cadmium and zinc at trace concentrations.
|
|
At times of stress, another form of asexual reproduction takes place that may allow some of the polyps to survive even though the parent colony dies. This has been termed "polyp bail-out" and involves growth of the coenosarc (the living tissue covering the skeleton) to isolate the polyp, detachment of the polyp, and settlement of the polyp on the seabed followed by its attachment and growth of a new skeleton. In the laboratory, about 5% of these polyps survived to found a new colony. This coral exhibits a high growth rate, high reproductive output and short life-span.
|
|
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.
|
|
Once the baby sharks are born, they are not taken care of by the parents in any way. Usually, a litter consists of 12 to 15 pups, except for the great hammerhead, which gives birth to litters of 20 to 40 pups. These baby sharks huddle together and swim toward warmer water until they are old enough and large enough to survive on their own. In 2007, the bonnethead shark was found to be capable of asexual reproduction via automictic parthenogenesis, in which a female's ovum fuses with a polar body to form a zygote without the need for a male.
|
|
As such, there are over 80 species of unisex reptiles (mostly lizards but including a single snake species), amphibians and fishes in nature for which males are no longer a part of the reproductive process. A female will produce an ovum with a full set (two sets of genes) provided solely by the mother. Thus, a male is not needed to provide sperm to fertilize the egg. This form of asexual reproduction is thought in some cases to be a serious threat to biodiversity for the subsequent lack of gene variation and potentially decreased fitness of the offspring.
|
|
Seedlings develop two structures or axes of growth, one that develops upward out of the soil, called stems, and structures that develop downward which are called roots. The roots are modified to have root hairs and branch indiscriminately with cells that take in water and nutrients, while the stems are modified to move water and nutrients to and from the leaves and flowers. Stems have nodes with buds where leaves and flowers arise at specific locations, while roots do not. Plants use under ground stems to multiply their numbers by asexual reproduction and to survive from one year to the next, usually over a period of dormancy.
|
|
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.
|
|
Examining non-model organisms can provide novel insights into the mechanisms underlying the "diversity of fascinating morphological innovations" that have enabled the abundance of life on planet Earth. In animals and plants, the "innovations" that cannot be examined in common model organisms include mimicry, mutualism, parasitism, and asexual reproduction. De novo transcriptome assembly is often the preferred method to studying non-model organisms, since it is cheaper and easier than building a genome, and reference-based methods are not possible without an existing genome. The transcriptomes of these organisms can thus reveal novel proteins and their isoforms that are implicated in such unique biological phenomena.
|
|
Though in most species at least part of the disc is needed for complete regeneration, in a few species of sea stars, a single severed arm can grow into a complete individual over a period of several months. In at least some of these species, they actively use this as a method of asexual reproduction. A fracture develops on the lower surface of the arm and the arm pulls itself free from the body which holds onto the substrate during the process. During the period of regrowth, they have a few tiny arms and one large arm, thus often being referred to as "comets".
|
|
Bdelloid rotifers are aquatic organisms and when their habitat dries up, they have the capability of going into a dormant state known as cryptobiosis to survive desiccation. They can remain in this state for periods of several years and when circumstances improve, they can revitalise in a few hours and continue with their normal activities. No male bdelloid rotifers have ever been found and it is believed that all bdelloid rotifers reproduce solely by means of asexual reproduction through the process of parthenogenesis. Molecular studies have shown that all bdelloid rotifers are descended from a common ancestor which lost its ability to reproduce sexually about 80 million years ago.
|
|
Anthopleura stellula is unusual among sea anemones in that it can divide by transverse fission. This is not a common method of asexual reproduction among these sea anemones but tends to occur as a reaction to stress, such as when an anemone is experiencing a lowering of the salinity. The fission involves the animal forming a transverse constriction before dividing in two, the oral portion growing a new pedal disc and the basal portion growing a new oral disc and pharynx. There are a few other sea anemones such as Gonactinia prolifera that can divide in this way, and all are rather small, primitive sea anemones with simple internal structures.
|
|
285x285pxThis species is found wild and cultivated in sandy-loamy soils of pH 4.34–5.01 with low cation-exchange capacity and high metal content. The vegetation type preferred is lowland and premontane, neotropical jungle where conditions of soil, precipitation and humidity are appropriate for its development. Despite being a monoecious species and prone to floral polygamy, Ilex guayusa appears to yield little fertile material, so it relies mostly on asexual reproduction (basal shoots, sprouts and suckers). In its initial growth stages, Ilex guayusa behaves as an understory species, becoming a shrub with spreading branches when it receives higher amounts of light, eventually becoming a tree.
|
|
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.
|
|
In order to increase the amount of successful sexual and asexual reproduction events, the species require hard surfaces within water depths ranging from the mean high water line to about 30 meters. In 2009, the United States government enacted the American Recovery and Reinvestment Act, which provided funding for coral conservation through the National Oceanic and Atmospheric Administration (NOAA) department. This funding allowed for the creation of a network of coral nurseries throughout the waters off the coast of southern Florida and the U.S. Virgin Islands for the recovery of Elkhorn coral. The nurseries have proven helpful in conducting genetic research in the facilitation of overall reef growth and restoration.
|
|
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.
|
|
Because bone vampires are extinct on their home planet of Doohan 6 and are capable of asexual reproduction, the crew releases Mr. Peppy into Doohan 6's wilderness to restore the species. Shortly after releasing Mr. Peppy, the crew learns from Doohan 6's locals that the bones of their livestock had been devoured by bone vampires, which led them to hunt the species to near-extinction. The planet's former bone vampire hunter Angus McZongo goes out to hunt Mr. Peppy when he seemingly breaks his vegetarian diet learned from Fry by attacking the planet's livestock. However, Fry decides to kill Mr. Peppy himself after he apparently attacks and injures Leela.
|
|
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.
|
|
They are nevertheless evident by the bump- like elevated areas along the cortical surface. Their abundance is conspicuous when the thallus is sectioned and examined under a dissecting microscope. Pycnidia in V. nylanderi are abundantly fertile as seen by conidia (conidium singular), which “are specialized, non-motile fungal spores,” that appear to function as re-establishing the lichen with an “appropriate photobiont,” a form of asexual reproduction,Bungartz, F. 2002. Morphology and anatomy of conidia-producing structures, Lichen Flora of the Greater Sonoran Desert 1: 35–40 in contrast to “sterile pycnidia (conidia not evident) in V. leopardina. Conidia may also to function as “male gametes (spermatia)”Sanders, W. B. 2014.
|
|
The space between the skin and gut is filled with mesenchyme, also known as parenchyma, a connective tissue made of cells and reinforced by collagen fibers that act as a type of skeleton, providing attachment points for muscles. The mesenchyme contains all the internal organs and allows the passage of oxygen, nutrients and waste products. It consists of two main types of cell: fixed cells, some of which have fluid-filled vacuoles; and stem cells, which can transform into any other type of cell, and are used in regenerating tissues after injury or asexual reproduction. Most platyhelminths have no anus and regurgitate undigested material through the mouth.
|
|
Microphallus turgidus exclusively uses the snail Potamopyrgus antipodarum as the first intermediate host, a shrimp as the secondary intermediate host, and the final hosts are typically waterfowl. Embryonated Microphallus turgidus eggs are ingested from sediment and hatch in the snail's gut, penetrate the intestine, and migrate to the gonads and digestive gland. Following successful establishment, the parasite then undergoes asexual reproduction, replacing much of the host's reproductive tissue and digestive gland, which results in complete sterilization of the snail. The first visible parasite developmental stages (blastocercariae) are detectable after approximately 75 days post- exposure and metacercariae are common by 90 days post-exposure at 16 °C in the lab.
|
|
A major drawback of sexual recombination is the separation of complexes of alleles that have adapted together. Study of Daphnia pulex, a microcrustacean that has the ability to reproduce sexually and asexually based upon which is advantageous at particular evolutionary time points, allows for direct quantification and comparison of recombination rates in mobile genetic elements in sexual and asexual lineages. This species of Daphnia's asexual lineage is rather young in an evolutionary time perspective and rapidly go extinct. It is hypothesized that this rapid extinction is caused by a loss of heterozygosity caused by asexual reproduction as well as gene conversion exposing them to pre-existing deleterious mutations.
|
|
However, these may have evolved well before the last common ancestor of eukaryotes given that meiosis is performed using the same proteins in all eukaryotes, perhaps stretching to as far back as the hypothesized RNA world. Cell organelles probably originated from free-living cyanobacteria (symbiogenesis) possibly after the evolution of phagocytosis (engulfing other cells) with the removal of the rigid cell wall which was only necessary for asexual reproduction. Mitochondria had already evolved in the Great Oxygenation Event, but plastids used in plants for namely photosynthesis are thought to have appeared about 1.6–1.5 Gya. Histones likely appeared during the Boring Billion to help organize and package the increasing amount of DNA in eukaryotic cells into nucleosomes.
|
|
All ciliates, including karyorelicteans, possess two different kinds of nucleus, which separate the functions of gene expression and sexual recombination. The macronuclei, or somatic nuclei, are the site of transcription, while the smaller micronuclei, or germline nuclei, are only active during sexual reproduction, where they first undergo meiosis to form gametic nuclei, which are exchanged when two mating cells conjugate. Two gametic nuclei fuse to form a zygotic nucleus, which divides by mitosis into two daughter nuclei, one of which develops into a new micronucleus and the other into a macronucleus; the old macronucleus typically disintegrates (see main article). In most ciliates, a macronucleus can divide during asexual reproduction to form new daughter macronuclei, through a process called amitosis.
|
|
On board the Prometheus, Hawking discovers the entire crew brutally murdered and the ship infested with large, hostile creatures. Retrieving the ship's science logs, Hawking discovers that Project Firestart was a genetic engineering program that sought to create a mining species resistant to extreme cold and low oxygen levels by combining the DNA of oxen with a new species of fungi discovered in asteroids around Titan. Hawking further learns that one of the scientists on the project, Dr. Annar, secretly altered the DNA of the mining creatures in an attempt to create a race of super soldiers. The plan backfired, as Annar's creations proved to be mindlessly hostile and capable of asexual reproduction.
|
|
Many felt the existence of microorganisms was evidence in support of spontaneous generation, since microorganisms seemed too simplistic for sexual reproduction, and asexual reproduction through cell division had not yet been observed. Van Leeuwenhoek took issue with the ideas common at the time that fleas and lice could spontaneously result from putrefaction, and that frogs could likewise arise from slime. Using a broad range of experiments ranging from sealed and open meat incubation and the close study of insect reproduction he became, by the 1680s, convinced that spontaneous generation was incorrect. The first experimental evidence against spontaneous generation came in 1668 when Francesco Redi showed that no maggots appeared in meat when flies were prevented from laying eggs.
|
|
Asexual reproduction compels genomes to be inherited as indivisible blocks so that once the least mutated genomes in an asexual population begin to carry at least one deleterious mutation, no genomes with fewer such mutations can be expected to be found in future generations (except as a result of back mutation). This results in an eventual accumulation of mutations known as genetic load. In theory, the genetic load carried by asexual populations eventually becomes so great that the population goes extinct. Also, laboratory experiments have confirmed the existence of ratchet and the consequent extinction of populations in many organisms (under intense drift and when recombinations are not allowed) including RNA viruses, bacteria, and eukaryotes.
|
|
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.
|
|
Antennaria soliceps is a rare species of flowering plant in the daisy family known by the common name Charleston Mountain pussytoes. It has been found only on Mount Charleston in Clark County in the southern part of the US state of Nevada.Biota of North America Program 2014 county distribution map Antennaria soliceps is a small plant rarely growing more than 2 inches (5 cm) from the ground, spreading by means of horizontal stems running along the surface of the ground. All known plants discovered to date are female, the species apparently relying exclusively on asexual reproduction. It grows on talus slopes near the tree line in the mountains, 3000–3400 meters (10,000–11,300 feet) above sea level.
|
|
Lifecycle of Toxoplasma gondii More detailed diagram. The feces of infected cats infects rodents hunted by cats, which rodents are more likely to be eaten by cats; it also infects animals bred for meat, which is a vector depending on how the meat is treated The lifecycle of T. gondii may be broadly summarized into two components: a sexual component that occurs only within cats (felids, wild or domestic), and an asexual component that can occur within virtually all warm-blooded animals, including humans, cats, and birds. Because T. gondii can sexually reproduce only within cats, cats are therefore the definitive host of T. gondii. All other hosts – in which only asexual reproduction can occur – are intermediate hosts.
|
|
The story is set in the year 3394, a thousand years after mankind flees from Earth after it was destroyed by a race of shapeshifting aliens – the , aboard hundreds of massive spaceships created from the remains of the planet. One such ship is the Sidonia, which has developed its own human culture closely based on that of Japan where human cloning, asexual reproduction, and human genetic engineering, such as granting humans photosynthesis, are commonplace. It is also revealed that the top echelons of this society have secretly been granted immortality. With a population of over 500,000 people, Sidonia is possibly the last human settlement remaining as the fates of the other ships are unknown.
|
|
In Down syndrome, the gene expression on chromosome 21 has increased 50%, and this results in significant health and mental disabilities (1 in 800 human live births have Down syndrome). Prokaryotes reproduce through asexual reproduction, usually by binary fission. The bacterial chromosome is present only in one copy per cell, but there can still be variation in gene dosage due to DNA replication which starts at the origin of replication and ends at the termination site. The genes that are closer to the origin site would be replicated first and would consequently be present in two copies in the cell for a longer time than the genes that are closer to the termination site.
|
|
Another mechanism typically observed in facultative parthenote reptiles is terminal fusion, in which a haploid polar body produced as a byproduct of normal female meiosis fuses with the egg cell to form a diploid nucleus, much as a haploid sperm cell fuses its nucleus with that of an egg cell to form a diploid genome during sexual reproduction. This method of parthenogenesis produces offspring that are homozygous at nearly all genetic loci, and inherit approximately half of their mother's genetic diversity. This form of parthenogenesis can produce male as well as WW- genotype females. Because the meiosis process proceeds normally in species employing this mechanism, they are capable of both sexual and asexual reproduction, as in the Komodo dragon and several species of snakes.
|
|
For example, the Amazonian frog Pristimantis ockendeni is actually at least three different species that diverged over 5 million years ago. Stabilizing selection has been invoked as a force maintaining similarity in species complexes, especially they adaptat to special environments, such as a host in the case of symbionts or extreme environments, constrains possible directions of evolution: in such cases, strongly divergent selection is not to be expected. Also, asexual reproduction, such as through apomixis in plants, may separate lineages without producing a great degree of morphological differentiation. Possible processes explaining similarity of species in a species complex: a – morphological stasis b – hybrid speciation A species complex is usually a group that has one common ancestor (a monophyletic group), but closer examination can sometimes disprove that.
|
|
This is one hypothesized reason for males having two penises instead of one: as each hemipenis is associated with one testis and only one side can be used during mating, having a second hemipenis functions as a "backup" and ensures that mating can continue even if one side were to run out of sperm. It is important to distinguish between cryptic female choice and facultative parthenogenesis, a form of asexual reproduction. Due to the female's ability to get pregnant long after she has been in contact with a male, it is difficult to distinguish between the two in ambiguous cases. In such circumstances, molecular testing techniques can be used to identify whether her offspring share all or some of their genetic make-up with their mother.
|
|
Lichen substances are primarily three terpenoid compounds, T3, zeorin and (-)-16 α-hydroxykaurane; bougeanic acid and salazinic acid occasionally present. Vermilacinia paleoderma is distinguished from V. procera by the surface of the branches having crater-like depressions in contrast to a relatively even surface of V. procera and by producing abundant fertile blackened pycnidia in contrast to mostly sterile pycnidia in V. procera. The black banding and spot patterns in V. procera may be related to morphogenesis of the pycnidia as reported in subgenus Cylindricaria for sterile pycnidia in V. leopardina, in contrast to abundant fertile pycnidia in V. nylanderi. The brittle thallus of V. procera cracking transversely, appearing to fracture off sections of the thallus, would seem to constitute asexual reproduction by fragmentation.
|
|
Some reptiles use the ZW sex-determination system, which produces either males (with ZZ sex chromosomes) or females (with ZW or WW sex chromosomes). Until 2010, it was thought that the ZW chromosome system used by reptiles was incapable of producing viable WW offspring, but a (ZW) female boa constrictor was discovered to have produced viable female offspring with WW chromosomes. The female boa could have chosen any number of male partners (and had successfully in the past) but on these occasions she reproduced asexually, creating 22 female babies with WW sex-chromosomes. Polyembryony is a widespread form of asexual reproduction in animals, whereby the fertilized egg or a later stage of embryonic development splits to form genetically identical clones.
|
|
Because sex combines genes from two individuals, sexually reproducing populations can more easily combine advantageous genes than can asexual populations. If, in a sexual population, two different advantageous alleles arise at different loci on a chromosome in different members of the population, a chromosome containing the two advantageous alleles can be produced within a few generations by recombination. However, should the same two alleles arise in different members of an asexual population, the only way that one chromosome can develop the other allele is to independently gain the same mutation, which would take much longer. Several studies have addressed counterarguments, and the question of whether this model is sufficiently robust to explain the predominance of sexual versus asexual reproduction remains.
|
|
In all parthenogenetic reptile species studied to date, chromosomal evidence supports the theory that parthenogenesis arose through a hybridization event, although members of the genus Lepidophyma may be exceptions to this rule. The original hybridization event is believed to occur between two related species and is often followed by backcrossing to either parent species to create triploid parthenogenetic offspring. As no crosses of two sexual species in captivity have ever produced parthenogenetic offspring, it is unclear how a hybridization event would actually lead to asexual reproduction. It is possible that parthenogenesis evolved as a way of overcoming sterility due to improper chromosomal pairing and segregation during meiosis in hybrids, and that rare hybrid individuals that could premeiotically duplicate their chromosomes could escape hybrid sterility by reproducing through parthenogenesis.
|
|
Over 1,000 cultivars have been chosen for particular characteristics, which are propagated by asexual reproduction most often by grafting, but some cultivars can also be propagated by budding, cuttings, tissue culture, or layering. Some cultivars are not in cultivation in the Western world or have been lost over the generations, but many new cultivars are developed each decade. Cultivars are chosen for phenotypical aspects such as leaf shape and size (shallowly to deeply lobed, some also palmately compound), leaf color (ranging from chartreuse through dark green or from orange to red, to dark purple, others variegated with various patterns of white and pink), bark texture and color, and growth pattern. Most cultivars are less vigorous and smaller than is typical for the species, but are more interesting than the relatively mundane species.
|
|
By mid-March 1837, barely six months after his return to England, Darwin was speculating in his Red Notebook on the possibility that "one species does change into another" to explain the geographical distribution of living species such as the rheas, and extinct ones such as the strange extinct mammal Macrauchenia, which resembled a giant guanaco, a llama relative. His thoughts on lifespan, asexual reproduction and sexual reproduction developed in his "B" notebook around mid-July on to variation in offspring "to adapt & alter the race to changing world" explaining the Galápagos tortoises, mockingbirds and rheas. He sketched branching descent, then a genealogical branching of a single evolutionary tree, in which "It is absurd to talk of one animal being higher than another", discarding Lamarck's independent lineages progressing to higher forms.
|
|
Aphids alternate between asexual reproduction in the Summer, i.e., when the environment is favorable and there is plenty of food, and sexually in the Fall when the organism is stressed by its environment. This has the biological advantage of ensuring identical copies of the parent will be well suited to take advantage of the favorable conditions, and variation in offspring in a stressful environment in hopes some of the offspring will find the environment favorable, even when the parents do not. The entire social construct in the novel is therefore an extrapolation of this idea onto a human culture, where successful female clans (female, because only they can produce offspring) can take advantage of their sociological niches by producing exact copies, and unsuccessful females produce variable offspring sexually.
|
|
This made Hwang the first, unknowingly, to successfully perform the process of parthenogenesis to create a human embryon and, ultimately, a human parthenogenetic stem cell line. Matchaki recreated Woo-Suk's experiment in 2019 with seven successful human parthenogenetic stem cell lines thereby proving single-gender asexual reproduction as a viable option in humans. Helen Spurway, a geneticist specializing in the reproductive biology of the guppy, Lebistes reticulatus, claimed, in 1955, that parthenogenesis, which occurs in the guppy in nature, may also occur (though very rarely) in the human species, leading to so-called "virgin births". This created some sensation among her colleagues and the lay public alike.TIME magazine, November 28, 1955; Editorial in The Lancet, 2: 967 (1955) Sometimes an embryo may begin to divide without fertilisation but it cannot fully develop on its own, so while it may create some skin and nerve cells, it cannot create others (such as skeletal muscle) and becomes a type of benign tumor called an ovarian teratoma.
|
|