The wood-inhabiting Ascomycetes and Basidiomycetes are either homothallic or heterothallic (Ryvarden and Gilbertson 1993). Homothallic fungi are self-fertile, that is no second mating type is required for sexual reproduction. Fertilization takes place at the same mycelium. Many Ascomycetes and about 10% of the Basidiomycetes belong to this type. Heterothallism includes both bipolar and tetrapolar fungi. In bipolar (uni-factorial) species, incompatibility is controlled by a series of multiple alleles at one locus. Any dikaryon has two alleles that segregate at the the basidiospores have one allele and half the other. Compatible matings occur between monokaryons with different mating type factors. The inbreeding level is 50%. The outbreeding level inpopulations of bipolar polypores is over 90%. In tetrapolar (bifactorial) species, incompatibility is controlled by two se-ries of multiple alleles at two loci on different chromosomes. The twopairs segregate independently at meiosi...
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