Genetics of secondarily homothallic basidiomycetes

Abstract

The random migration of meiotic products to give binucleate spores in secondarily homothallic basidiomycetes gives frequencies of nuclear association which have not previously been recognised. For a single segregating factor in two-spored species, the probability of a basidiospore receiving unlike nuclei is twice that of it receiving like nuclei. Consequently random spore progenies can be expected to yield genotypic ratios of 1:4: 1 with the heteroallelic class predominating. If eight nuclei are present in the basidia of four-spored species then random migration would favour unlike over like pairing in the proportion 4:3; this would give a genotypic ratio of 3: 8:3. Extrapolations are made for two and n factors, and the expected phenotypic ratios for mating-type factors, auxotrophic markers and sporophore characters are derived. Second division segregation and chromosome mapping are also considered. Random nuclear migration in secondarily homothallic basidiomycetes favours heteroallelism and provides a simple explanation for the regularly observed preponderance of isolates heteroallelic for mating-type. © 1980 The Genetical Society of Great Britain.