![Isogamy](https://upload.wikimedia.org/wikipedia/commons/d/d5/Isogamy.svg)
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 tha ...
that involves
gametes of the same
morphology
Morphology, from the Greek and meaning "study of shape", may refer to:
Disciplines
*Morphology (archaeology), study of the shapes or forms of artifacts
*Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
(indistinguishable in shape and size), found in most
unicellular eukaryotes.
Because both gametes look alike, they generally cannot be classified as
male
Male (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 reproduce sexually without access to ...
or
female
Female (Venus symbol, symbol: ♀) is the sex of an organism that produces the large non-motile ovum, ova (egg cells), the type of gamete (sex cell) that fuses with the Sperm, male gamete during sexual reproduction.
A female has larger gamet ...
. Instead, organisms undergoing isogamy are said to have different
mating types
In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. ''Fertilization'' is the fusion of two gametes. ''Copulation'' is the union of the sex organs of two sexually reproduc ...
, 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. Proce ...
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 multicellula ...
.
Evolution
It is generally accepted that isogamy is an ancestral state for anisogamy
and that isogamy was the first stage in the evolution 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 tha ...
. Isogamous reproduction evolved independently in several lineages of plants and animals to
anisogamous
Different forms of anisogamy: A) anisogamy of motile cells, B) egg_cell.html"_;"title="oogamy_(egg_cell">oogamy_(egg_cell_and_sperm_cell),_C)_anisogamy_of_non-motile_cells_(egg_cell_and_spermatia)..html" ;"title="egg_cell_and_sperm_cell.html" ;" ...
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 t ...
s of male and
female
Female (Venus symbol, symbol: ♀) is the sex of an organism that produces the large non-motile ovum, ova (egg cells), the type of gamete (sex cell) that fuses with the Sperm, male gamete during sexual reproduction.
A female has larger gamet ...
types and subsequently to
oogamous
Oogamy is an extreme form of anisogamy where the gametes differ in both size and form.
In oogamy the large female gamete (also known as ovum) is immobile, while the small male gamete (also known as sperm) is mobile. Oogamy is a common form of an ...
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
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 tha ...
.
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 ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
such as
baker's yeast and
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
. Many species of green algae are isogamous. It is typical in the genera ''
Ulva
Ulva (; gd, Ulbha) is a small island in the Inner Hebrides of Scotland, off the west coast of Mull. It is separated from Mull by a narrow strait, and connected to the neighbouring island of Gometra by a bridge. Much of the island is formed from ...
'', ''
Hydrodictyon
The water net (genus ''Hydrodictyon'') is a taxon of freshwater green algae in the family Hydrodictyaceae. ''Hydrodictyon'' does well in clean, eutrophic water, and has become a nuisance in New Zealand, where it has been recently introduced. Th ...
'', ''
Tetraspora
''Tetraspora'' is a genus of green algae in the family Tetrasporaceae of the order Chlamydomonadales, division Chlorophyta. Species of ''Tetraspora'' are unicellular green algae that exist in arrangements of four and consist of cells being packa ...
'', ''
Zygnema
''Zygnema'' is a genus of freshwater filamentous thalloid alga
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multi ...
'', ''
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 i ...
'', 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.
See also
Biology
*
Anisogamy
Different forms of anisogamy: A) anisogamy of motile cells, B) egg_cell.html"_;"title="oogamy_(egg_cell">oogamy_(egg_cell_and_sperm_cell),_C)_anisogamy_of_non-motile_cells_(egg_cell_and_spermatia)..html" ;"title="egg_cell_and_sperm_cell.html" ;" ...
*
Evolution of sexual reproduction
Sexual reproduction is an adaptive feature which is common to almost all multicellular organisms and various unicellular organisms, with some organisms being incapable of asexual reproduction. Currently the adaptive advantage of sexual reprodu ...
*
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 t ...
*
Mating in fungi
Mating in fungi is a complex process governed by mating types. Research on Fungus, fungal mating has focused on several model species with different behaviour. Not all fungi reproduce sexually and many that do are isogamy, isogamous; thus, for man ...
*
Meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
*
Oogamy
Oogamy is an extreme form of anisogamy where the gametes differ in both size and form.
In oogamy the large female gamete (also known as ovum) is immobile, while the small male gamete (also known as sperm) is mobile. Oogamy is a common form of a ...
*
Sex
Sex is the trait that determines whether a sexually reproducing animal or plant produces male or female gametes. Male plants and animals produce smaller mobile gametes (spermatozoa, sperm, pollen), while females produce larger ones (ova, oft ...
Social anthropology
*
Hypergamy
*
Hypogamy
Hypergamy (colloquially referred to as "marrying up") is a term used in social science for the act or practice of a person marrying a spouse of higher caste or social status than themselves.
The antonym "hypogamy" refers to the inverse: marry ...
Notes and references
*
{{Sex (biology)
Reproduction
Germ cells
Charophyta