Cell fusion (plasmogamy or syngamy) is a stage in the Amoebozoa sexual cycle.
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When a tick ingests the piroplasms, the parasites undergo syngamy in the gut and can move to hemolymph. The motile kinetes can infect the salivary glands. From this, sporogony occurs to create sporozoites to continue the life cycle.
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Elphidium exhibits an alternation of generation in its life cycle. The megalosperic forms alternates with microspheric forms. The microspheric forms are developed by the conjugation or syngamy. It means there is always an alternations of asexual (microspheric) and sexual (megalospheric) generation in Elphidium.
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Microbial eukaryotes can be either haploid or diploid, and some organisms have multiple cell nuclei.See coenocyte. Unicellular eukaryotes usually reproduce asexually by mitosis under favorable conditions. However, under stressful conditions such as nutrient limitations and other conditions associated with DNA damage, they tend to reproduce sexually by meiosis and syngamy.
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Some relatively unusual forms of reproduction are: Gynogenesis: A sperm stimulates the egg to develop without fertilisation or syngamy. The sperm may enter the egg. Hybridogenesis: One genome is eliminated to produce haploid eggs. Canina meiosis: (sometimes called "permanent odd polyploidy") one genome is transmitted in the Mendelian fashion, others are transmitted clonally.
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If the protists reproduce asexually, they do so through binary fission, multiple fission, budding, and fragmentation. If the protists reproduce sexually, they do so through a syngamy process where there is a fusion of the gametes. If this occurs in an individual it is recognized as autogamy. If this occurs between individuals, it is known as conjugation.
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Isogametes of two different individuals fuse in pairs to form zygotes. These are then develops into microspheric form. The life cycle of Elphidium may be summarized as follows: the microspheric forms produce amoebulae by asexual fission which develops into megalospheric forms. The megalospheric forms produce flagellated isogametes which after syngamy produce zygotes that develop into microspheric forms.
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The gametes conjugate outside in open sea to produce zygotes and the B form then develops and matures during the second summer. Lister (1895) observed Elphidium in two different forms as megalospheric form (sexual form) and microsperic form (asexual form). The megalosperic form was developed from the microsperic form. The gametes which gives rise to microspheric form by syngamy.
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The haploid gametes (daughter cells produced after meiosis) were discovered in 2014. The haploid trypomastigote-like gametes can interact with each other via their flagella and undergo cell fusion (the process is called syngamy). Thus, in addition to binary fission, T. brucei can multiply by sexual reproduction. Trypanosomes belong to the supergroup Excavata and are one of the earliest diverging lineages among eukaryotes.
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Each amoebula secretes the proloculum, formsrhizopodia, then it grows and forms other chambers of the shell to become a megalospheric forms. The megalospheric form reproduces sexually by syngamy or conjugation. During sexual reproduction in megalospheric forms, nucleus first breaks up into many small nuclei and the cytoplasm collects around each of these nuclei. The nuclei divide twice giving rise to a large haploid and known as isogametes.
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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.
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Eukaryotic pathogens are often capable of sexual interaction by a process involving meiosis and syngamy. Meiosis involves the intimate pairing of homologous chromosomes and recombination between them. Examples of eukaryotic pathogens capable of sex include the protozoan parasites Plasmodium falciparum, Toxoplasma gondii, Trypanosoma brucei, Giardia intestinalis, and the fungi Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans. Viruses may also undergo sexual interaction when two or more viral genomes enter the same host cell.
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In this specialized region, diploid and haploid nuclei can both be found, but the exact mechanism of diploidization is poorly understood (Brück and Schnetter 1997). This means that in Bryopsis diploidization to produce microthalli is not dependent on syngamy, it can happen within the macrothallus. This can be disadvantageous due to the loss of genetic exchange, but it is advantageous because the direct development of microthalli does not depend on mating so new microthalli can be produced relatively quickly.
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In Paramecium tetraurelia, vitality declines over the course of successive asexual cell divisions by binary fission. Clonal aging is associated with a dramatic increase in DNA damage. When paramecia that have experienced clonal aging undergo meiosis, either during conjugation or automixis, the old macronucleus disintegrates and a new macronucleus is formed by replication of the micronuclear DNA that had just experienced meiosis followed by syngamy. These paramecia are rejuvenated in the sense of having a restored clonal lifespan.
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After being fertilised, the ovary starts to swell and develop into the fruit. With multi-seeded fruits, multiple grains of pollen are necessary for syngamy with each ovule. The growth of the pollen tube is controlled by the vegetative (or tube) cytoplasm. Hydrolytic enzymes are secreted by the pollen tube that digest the female tissue as the tube grows down the stigma and style; the digested tissue is used as a nutrient source for the pollen tube as it grows.
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Sexual phenomena have not been directly observed in Amoeba, although sexual exchange of genetic material is known to occur in other Amoebozoan groups. Most amoebozoans appear capable of performing syngamy, recombination and ploidy reduction through a standard meiotic process. The “asexual” model organism Amoeba proteus has most of the proteins associated with sexual processes. In cases where organisms are forcibly divided, the portion that retains the nucleus will often survive and form a new cell and cytoplasm, while the other portion dies.
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Sex may also be derived from another prokaryotic process. A comprehensive theory called "origin of sex as vaccination" proposes that eukaryan sex-as-syngamy (fusion sex) arose from prokaryan unilateral sex-as-infection, when infected hosts began swapping nuclearised genomes containing coevolved, vertically transmitted symbionts that provided protection against horizontal superinfection by other, more virulent symbionts. Consequently, sex-as-meiosis (fission sex) would evolve as a host strategy for uncoupling from (and thereby render impotent) the acquired symbiotic/parasitic genes.
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One sperm fertilizes the egg cell and the other sperm combines with the two polar nuclei of the large central cell of the megagametophyte. The haploid sperm and haploid egg combine to form a diploid zygote, the process being called syngamy, while the other sperm and the two haploid polar nuclei of the large central cell of the megagametophyte form a triploid nucleus (triple fusion). Some plants may form polyploid nuclei. The large cell of the gametophyte will then develop into the endosperm, a nutrient-rich tissue which provides nourishment to the developing embryo.
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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.
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It has been estimated that there may be 75 distinct lineages of eukaryotes. Most of these lineages are protists. The known eukaryote genome sizes vary from 8.2 megabases (Mb) in Babesia bovis to 112,000–220,050 Mb in the dinoflagellate Prorocentrum micans, showing that the genome of the ancestral eukaryote has undergone considerable variation during its evolution. The last common ancestor of all eukaryotes is believed to have been a phagotrophic protist with a nucleus, at least one centriole and cilium, facultatively aerobic mitochondria, sex (meiosis and syngamy), a dormant cyst with a cell wall of chitin and/or cellulose and peroxisomes.
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