Isogamous

Isogamy is a form of sexual reproduction in which the gametes produced by different mating types are morphologically indistinguishable. In isogamous species, the two gametes are typically similar in size and appearance, and fertilization depends on compatibility rather than visible differences in gamete form. This contrasts with anisogamy, where gametes differ in size, and with oogamy, where a large, non-motile egg fuses with a small, motile sperm.

In many isogamous organisms, mating-type identity is genetically determined and maintained by biochemical signaling rather than by distinct sexes. Gametes may be motile and pair up in response to pheromones or other cues that indicate compatibility. After fusion, a zygote forms and can give rise to offspring through various life cycle pathways, which may include haploid or diploid stages depending on the lineage.

Isogamy occurs in a variety of organisms, notably among some green algae such as Chlamydomonas reinhardtii, as well as in several fungi and other protists. In fungi, two mating types that produce morphologically similar gametes engage in fusion to complete sexual reproduction. The isogamous mode is often described as ancestral to the evolution of anisogamy and oogamy in lineages where differential gamete investment later arose.

Overall, the term isogamy emphasizes the lack of morphological differentiation between gametes, with compatibility and signaling playing key roles in fertilization.