Contents 1 Evolution 2 Biological types 2.1 With motile cells 2.2 With non-motile cells 2.3 Conjugation 3 See also 3.1 Biology 3.2 Social anthropology 4 Notes and references

Evolution[edit] It appears that isogamy was the first stage of sexual reproduction. In several lineages (plants, animals), this form of reproduction independently evolved to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is very much larger than the male and has no ability to move. There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction.[1] In Ascomycetes, anisogamy (sexes) evolved from isogamy before mating types.[2][not in citation given]

Biological types[edit] With motile cells[edit] There are several types of isogamy. Both gametes may be flagellated and thus motile. This type occurs for example in algae such as some but not all species of Chlamydomonas. With non-motile cells[edit] In another type, neither of the gametes is flagellated. This is the case for example in the mating of yeast. Yeast mating types are commonly noted as "a" and "α" (alpha) instead of "+" and "-". Conjugation[edit] Another, more complex form, is conjugation (similar to the exchange of genetic material through a bridge in bacterial conjugation, but involving reproduction). This occurs in some the green algae, the Zygnematophyceae, e.g., Spirogyra. These algae grow as filaments of cells. When two filaments of opposing mating types come close together, the cells form conjugation tubes between the filaments. Once the tubes are formed, one cell balls up and crawls through the tube into the other cell to fuse with it, forming a zygote. In ciliates, cell fission may follow self-fertilization (autogamy), or it may follow conjugation (exchange of nuclei). In zygomycetes fungi, two hyphae of opposing mating types form special structures called gametangia where the hyphae touch. The gametangia then fuse into a zygosporangium. In other fungi, cells from two hyphae with opposing mating types fuse, but only the cytoplasm is fused (plasmogamy). The two nuclei do not fuse, leading to the formation of a dikaryon cell that gives rise to a mycelium consisting of dikaryons. Karyogamy (fusion of nuclei) then eventually occurs in sporangia, and leads to the formation of diploid cells (zygotes) that immediately undergo meiosis to form spores. Spirogyra conjugation In many cases, isogamous fertilization is used by organisms that can also reproduce asexually through binary fission, budding, or asexual spore formation. The switch to sexual reproduction mode is often triggered by a change from favorable to unfavorable growing conditions.[3] Fertilization often leads to the formation of a thick-walled zygotic resting spore that can withstand harsh environments and will germinate once growing conditions turn favorable again.

See also[edit] Biology[edit] Anisogamy Evolution of sexual reproduction Gamete Mating in fungi Meiosis Oogamy Sex Social anthropology[edit] Hypergamy Hypogamy

Notes and references[edit] ^ Dusenbery, David B. (2009). Living at Micro Scale, Chapter 20. Harvard University Press, Cambridge, Mass. ISBN 978-0-674-03116-6. ^ Beukeboom, L. and Perrin, N. (2014). The Evolution of Sex Determination. Oxford University Press, p. 10 [1]. Online resources, [2]. ^ Bernstein, H; Bernstein, C; Michod, RE (2011). "Meiosis as an Evolutionary Adaptation for DNA Repair". In Inna Kruman. DNA Repair. InTech. ISBN 978-953-307-697-3.  Sa Geng; Peter De Hoff; James G. Umen (July 8, 2014). "Evolution of Sexes from an Ancestral Mating-Type Specification Parthway". PLOS Biology. doi:10.137/journal.pbio.10001904.  v t e Sex Biological terms Sexual dimorphism Male Female Sexual differentiation Feminization Virilization Sex-determination system XY ZW XO Temperature-dependent Haplodiploidy Heterogametic sex Homogametic sex Sex chromosome X chromosome Y chromosome Testis-determining factor Hermaphrodite Sequential hermaphroditism Intersex Sexual reproduction Evolution of sexual reproduction Anisogamy Isogamy Germ cell Reproductive system Sex organ Meiosis Gametogenesis Spermatogenesis Oogenesis Gamete spermatozoon ovum Fertilization External Internal Sexual selection Plant reproduction Fungal reproduction Sexual reproduction in animals Sexual intercourse Human reproduction Sexuality Plant sexuality Animal sexuality Human sexuality Mechanics Differentiation Activity Sex portal Biology portal Retrieved from "" Categories: ReproductionGerm cellsCharophytaHidden categories: Articles needing additional references from December 2009All articles needing additional referencesAll articles with failed verificationArticles with failed verification from May 2017

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