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Mating types are molecular mechanisms that regulate compatibility in sexually reproducing eukaryotes. They occur in isogamous and anisogamous species. Depending on the group, different mating types are often referred to by numbers, letters, or simply "+" and "-" instead of "male" and "female", that refer to "sexes" or differences in size between gametes. Syngamy can only take place between gametes carrying different mating types.
Reproduction regulated by mating types is especially prevalent in fungi. Ascomycetes usually have two mating types referred to as "Mat 1-1" and "Mat 1-2" or in the case of yeast as "a" and "α" (alpha). Mating type genes in ascomycetes are called idiomorphs rather than alleles due to the uncertainty of the origin by common descent. The proteins they encode are transcription factors that regulate both the early and late stages of the sexual cycle. Heterothallic ascomycetes produce gametes that present a single Mat idiomorph and syngamy will only be possible between gametes carrying complementary mating types. On the other hand, homothallic ascomycetes produce gametes that can fuse with every other gamete in the population (including its own mitotic descendants) most often because each haploid contains the two alternate forms of the Mat locus in its genome. Basidiomycetes on the other hand can have thousands of different mating types.
The adaptive function of mating type in the ascomycete Neurospora crassa is discussed in the article Neurospora crassa. That matings in N. crassa are restricted to interaction of strains of opposite mating type may be an adaptation to promote some degree of outcrossing. Outcrossing, through complementation, could provide the benefit of masking recessive deleterious mutations in genes that function in the dikaryon and/or diploid stage of the life cycle.
- C.J. Alexopolous, Charles W. Mims, M. Blackwell, Introductory Mycology, 4th ed. (John Wiley and Sons, Hoboken NJ, 2004) ISBN 0-471-52229-5
- "From Mating Types to Sexes." In: Bachtrog D, Mank JE, Peichel CL, Kirkpatrick M, Otto SP, et al. (2014) Sex Determination: Why So Many Ways of Doing It? PLoS Biol 12(7): e1001899. doi:10.1371/journal.pbio.1001899