heterothallism
Heterothallism is a mating system found in some fungi and algae where an individual thallus is unable to produce viable offspring through self-fertilization and requires mating with a compatible thallus of the opposite mating type. This contrasts with homothallism, where an individual thallus can undergo self-fertilization and produce viable offspring. The genetic basis for heterothallism typically involves one or more genes that control mating type. In many fungi, these are referred to as mating-type loci (MAT loci).
There are two primary forms of heterothallism: primary and secondary. Primary heterothallism, also known as unisexual
The evolutionary advantage of heterothallism is thought to lie in promoting outcrossing and increasing genetic diversity