Isogamy is a form of

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote th ...

that involves gametes of the same morphology (indistinguishable in shape and size), found in most unicellular eukaryotes. Because both gametes look alike, they generally cannot be classified as

male Male (Mars symbol, symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot sexual reproduction, repro ...

female Female (symbol: ♀) is the sex of an organism that produces the large non-motile ova (egg cells), the type of gamete (sex cell) that fuses with the male gamete during sexual reproduction. A female has larger gametes than a male. Females a ...

. Instead, organisms undergoing isogamy are said to have different mating types, most commonly noted as "+" and "−" strains.

Etymology

The literal meaning of isogamy is "equal marriage" which refers to equal contribution of resources by both gametes to a zygote. The term isogamous was first used in the year 1887.

Characteristics of isogamous species

Isogamous species often have two mating types. Some isogamous species have more than two mating types, but the number is usually lower than ten. In some extremely rare cases a species can have thousands of mating types. In all cases,

fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Pro ...

occurs when gametes of two different mating types fuse to form a

zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicell ...

Evolution

It is generally accepted that isogamy is an ancestral state for anisogamy and that isogamy was the first stage in the evolution of

. Isogamous reproduction evolved independently in several lineages of plants and animals to anisogamous species with

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...

s of male and

types and subsequently to oogamous species in which the female gamete is very 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

. Isogamy is the norm in unicellular eukaryote species, although it is possible that isogamy is evolutionarily stable in multicellular species.

Occurrence

Almost all unicellular eukaryotes are isogamous. Among multicellular organisms, isogamy is restricted to

fungi A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...

such as

baker's yeast Baker's yeast is the common name for the strains of yeast commonly used in baking bread and other bakery products, serving as a leavening agent which causes the bread to rise (expand and become lighter and softer) by converting the fermentable ...

and

algae Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from ...

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

Ulothrix ''Ulothrix'' is a genus of green algae in the family Ulotrichaceae. ''Ulothrix'' is a genus of non-branching filamentous green algae, generally found in fresh and marine water. Its cells are normally as broad as they are long, and they thrive in ...

'', and ''

Chlamydomonas ''Chlamydomonas'' is a genus of green algae consisting of about 150 speciesSmith, G.M. 1955 ''Cryptogamic Botany Volume 1. Algae and Fungi'' McGraw-Hill Book Company Inc of unicellular flagellates, found in stagnant water and on damp soil, ...

''. Many fungi are isogamous.

Notes and references

* {{Sex (biology) Reproduction Germ cells Charophyta

Etymology

Characteristics of isogamous species

Evolution

Occurrence

See also

Biology

Social anthropology

Notes and references