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Homothallic refers to the possession, within a single organism, of the resources to reproduce sexually; [1] i.e., having male and female reproductive structures on the same thallus. The opposite sexual functions are performed by different cells of a single mycelium. [2] It can be contrasted to heterothallic. It is often used to categorize fungi.
Heterothallic species have sexes that reside in different individuals. The term is applied particularly to distinguish heterothallic fungi , which require two compatible partners to produce sexual spores, from homothallic ones, which are capable of sexual reproduction from a single organism.
Homothallic species are able to mate with themselves, while in heterothallic species only isolates of opposite mating types can mate. Mating between isogamous fungi may consist only of a transfer of a nucleus from one cell to another. Vegetative incompatibility within species often prevents a fungal isolate from mating with another isolate.
Those fungi that need a partner to mate are referred to as heterothallic (self-sterile), and those fungi not needing a partner are referred to as homothallic (self-fertile). A study of DNA sequences of mating type loci from different heterothallic and homothallic species in the genus Cochliobolus suggests that homothallism can be derived from ...
A homothallic strain of Closterium forms selfing zygospores via the conjugation of two sister gametangial cells derived from one vegetative cell. [8] Conjugation in the homothallic strain occurs mainly at low cell density and is regulated by an ortholog of a heterothallic sex-specific pheromone.
Heterothallic matings are initiated by fusion of haploid cells (gametes) from two strains of opposite mating type. This contrasts with homothallic strains that appear to express both mating types. [7] Mating is initiated by gametogenesis that produces small, motile gametes that fuse to form a small binucleate cell. The volume of the binucleate ...
These fungi are said to be homothallic, versus the normal heterothallic species with mating types. Others are secondarily homothallic, in that two compatible nuclei following meiosis migrate into each basidiospore, which is then dispersed as a pre-existing dikaryon. Often such species form only two spores per basidium, but that too varies.
Because heterothallic species necessarily undergo some degree of outcrossing they may benefit from a higher efficiency of selection because of higher effective recombination rates. In contrast, pseudohomothallic and homothallic species do not outcross (or rarely) and do not experience these benefits: in homothallics a reduced efficiency of ...