Homothallism
Homothallic refers to the possession, within a single organism, of the resources to reproduce sexually 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. It can be contrasted to heterothallic. It is often used to categorize fungi. In yeast, heterothallic cells have mating types
a and
α. An experienced mother cell will switch mating type every cell division cycle because of the
HO allele. Sexual reproduction commonly occurs in two fundamentally different ways in fungi. These are outcrossing in which two different individuals contribute nuclei to form a zygote, and self-fertilization or selfing in which both nuclei are derived from the same individual. Among the 250 known species of aspergilli, about 36% have an identified sexual state. Among those
Aspergillus species for which a sexual cycle has been observed, the majority in nature are homothallic. Selfing in the homothallic fungus
Aspergillus nidulans involves activation of the same mating pathways characteristic of sex in outcrossing species, i.e.