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Tetraploid Saccharomyces
Abstract
Summary: A yeast hybrid heterozygous for many alleles produces an occasional ascus in which instead of the expected 2 dominant:2 recessive segregations one finds 4 dominant:0 recessive ratios for most of the characters. The single ascospore cultures are often incapable of copulating with either mating type. Genetical analysis has revealed that such asci contain ascospores which are diploid and heterozygous for the mating type alleles and other characters. The single ascospore cultures, heterozygous for mating type, may sporulate and by characterization of their progeny the genotype of the ascospore can be determined. Other diploid cultures originating from single ascospores are homozygous for mating type. Cells from these cultures (unlike the diploid cells heterozygous for mating type) are capable of mating, and when mated with similar cells of complementary mating type produced tetraploid yeasts. Triploids were produced by mating diploids with haploids. The tetraploid segregates to produce the expected tetrad types and gametic ratios. Some sporulating cultures produced unexpected types of asci for characters controlling sugar fermentation but interpretation of their significance is not feasible since our customary control of breeding procedure does not apply in the analysis of diploid cultures which sporulate on ordinary agar slants.
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© Society for General Microbiology, 1951