Mating types occur in eukaryotes that undergo sexual reproduction via isogamy. Since the gametes of different mating types look alike, they are often referred to by numbers, letters, or simply "+" and "-" instead of "male" and "female." Mating (fertilization or conjugation) can only take place between different mating types.
Isogamic reproduction via mating types is especially prevalent in fungi. Ascomycetes usually have two mating types referred to as "+" and "-" or in the case of yeast as "a" and "α" (alpha). Basidiomycetes on the other hand can have thousands of different mating types.
Nothing in the morphology reveals that the cells or hyphae are either "+" or "-" but they are distinguished as being two forms of the same species. Mating types differ genetically by having two or more distinct alleles at a mating-type region in their genome. These genes typically code for cell surface components that are important in the interaction between different mating types. This interaction between different components is necessary to have sexual reproduction.
- Each mating type can signal its presence to others, (the "female" signals the "male" first by definition). This is done using pheromones, steroids, or carotenoids.
- In addition to "male" and "female," there may also be a distinction between strong and weak (e.g. strong female). In saccharomyces, there is a very complex system of mating type alternation from alpha to a through genetic recombination.
- C.J. Alexopolous, Charles W. Mims, M. Blackwell, Introductory Mycology, 4th ed. (John Wiley and Sons, Hoboken NJ, 2004) ISBN 0-471-52229-5