Evolution of mating types
The biological importance of the existence of functional anisogamy lies in the fact that it ensures that zygotes are not formed by combination of mutually related cells, in the extreme case gametes produced by a single individual (autogamy) but, where possible, by cells derived from different individuals (alogamy). However, the advantages of alogamy are not entirely apparent at first glance, especially the advantages for the individual. It can be advantageous for a population or the species as a whole if unrelated individuals can mate together. It holds more or less for most of the models that explain the existence of sexual reproduction as a mechanism increasing the evolutionary potential of the species that the favorable effect of sexual reproduction increases with increasing genetic difference of the mating individuals. However, for the individual, the inability to mate with the members of the same mating type is a limiting factor and thus generally disadvantageous. Thus, it is necessary to explain why individuals do not emerge in the population that would be capable of mating with all the members of their species, without respect to their mating type.