[Genetic express-test for distinguishing between haploids and autodiploids in the yeast Saccharomyces]

Some originally haploid strains of yeast Peterhof breeding stocks obtained in tetrad analysis of diploids turned out to be spontaneous autodiploids after storage. They produced polyploid hybrids, as shown by tetrad analysis. An express-test for discrimination between haploids and autodiploids, based on the frequency of mitotic homozygotisation for a recessive marker has been developed. It is 10-100 times higher in heterozygous diploids than in duplex triploids. Tester strains bearing selective recessive lys2, sup1 or sup2 marker have been obtained. The hybrids of the tester strains and those to be tested were plated on media selective for mitotic segregants homozygous for lys2 (medium with alpha-aminoadipic acid and lysine) or sup1, sup2 (medium without adenine, while the hybrid was homozygous for ochre nonsense ade1-6 suppressible by either sup1 or sup2); UV-induced mitotic homozygotisation was scored. By our method, we have shown that spontaneous autodiploids constitute 70% of strains under investigation in Peterhof breeding stocks.