Isogamy

 ( Reproduction ) 

[[File:Isogamy.svg|thumb|Different forms of isogamy:

A) isogamy of motile cells, B) isogamy of non-motile cells, C) conjugation (isogamy in the broad sense)|270x270px]] Isogamy is a form of sexual reproduction that involves Gamete of the same morphology (indistinguishable in shape and size), and is found in most unicellular eukaryotes. Because both gametes look alike, they generally cannot be classified as male or female.

Instead, organisms that reproduce through isogamy are said to have different Mating type, most commonly noted as "+" and "−" strains.

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Etymology The etymology of isogamy derives from the Greek adjective isos (meaning equal) and the Greek verb gameo (meaning to have sex/to reproduce), eventually meaning "equal reproduction" which refers to a hypothetical initial model of equal contribution of resources by both gametes to a zygote in contrast to a later evolutional stage of anisogamy.

(2016). 9780128004265, Academic Press. . ISBN 9780128004265

The term isogamy was first used in the year 1891.

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Characteristics of isogamous species Isogamous species often have two Mating type (heterothallism), but sometimes can occur between two Ploidy individuals that are mitotic descendents (homothallism). Some isogamous species have more than two mating types, but the number is usually lower than ten. In some extremely rare cases, such as in some Basidiomycota species, a species can have thousands of mating types.

Under the strict definition of isogamy, fertilization occurs when two Gamete fuse to form a zygote. Sexual reproduction between two cells that does not involve gametes (e.g. conjugation between two Mycelium in basidiomycete fungi), is often called isogamy, although it is not technically isogametic reproduction in the strict sense.

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Evolution

As the first stage in the evolution of sexual reproduction in all known life, isogamy is thought to have evolved just once, in a single unicellular eukaryote species, the common ancestor of all eukaryotes. It is generally accepted that isogamy is an ancestral state for anisogamy.

(2008). 9780080919874, Academic Press. . ISBN 9780080919874

Isogamous reproduction evolved independently in several lineages of plants and animals into anisogamy (species with of male and female types) and subsequently into oogamy (species in which the female gamete is much larger than the male and has no ability to move). This pattern may have been driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction.Dusenbery, David B. (2009). Living at Micro Scale, Chapter 20. Harvard University Press, Cambridge, Massachusetts .

Since it appeared, isogamy has remained the norm in unicellular eukaryote species, and it is possible that isogamy is also evolutionarily stable in multicellular species.

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Occurrence

Almost all unicellular eukaryotes are isogamous.

Graham Bell (2025). 9780198569725, OUP Oxford. . ISBN 9780198569725

Among multicellular organisms, isogamy is restricted to fungi and eukaryotic algae.

(2011). 9781139500821, Cambridge University Press. . ISBN 9781139500821

Many species of green algae are isogamous. It is typical in the genera Ulva, Hydrodictyon, Tetraspora, Zygnema, Spirogyra, Ulothrix, and Chlamydomonas.

O. P. Sharma (1986). 9780074519288, Tata McGraw-Hill Education. . ISBN 9780074519288

Many fungi are also isogamous, including single-celled species such as Saccharomyces cerevisiae and Schizosaccharomyces pombe.

(2020). 9781555819583, John Wiley & Sons. . ISBN 9781555819583

In some multicellular fungi, such as Basidiomycota, sexual reproduction takes place between two Mycelium, but there is no exchange of gametes.

There are no known examples of isogamous Animal, red algae or land plants.

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See also

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Biology

• Anisogamy
• Evolution of sexual reproduction
• Gamete
• Mating in fungi
• Meiosis
• Oogamy
• Sex

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Social anthropology

• Hypergamy
• Hypogamy

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Notes

Categories: Reproduction, Germ Cells, Charophyta

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