Analysis of hybrids obtained by rare-mating of Saccharomyces strains

Summary

Rare-mating of closely related Saccharomyces cerevisiae and S. diastaticus strains led to the formation of different hybrids. Mating-type switching and chromosome losses could be observed by means of classical genetic analysis and pulsed field gel electrophoresis of intact chromosomes. The latter was facilitated by extensive chromosome length polymorphism in both strains. When crossing the two haploid strains S. cerevisiae 41 α and S. diastaticus ATCC 28339 α, two different types of hybrids occurred. Both types showed complete addition of both parental genomes, one aα-status and the other αα-status. The αα-status could be explained by assuming a transient premutational lesion in MAT α. Usually lesions are repaired after a mating event and the α-mating type is restored. When crossing a diploid S. diastaticus strain, isogenic to the one previously mentioned, with the haploid S. cerevisiae strain, three different types of hybrids could be distinguished regarding their mating-types. It was possible to prove that the haploid S. diastaticus strain ATCC 28339 is disomic and the diploid hybrid, named 41ATCC-b, is trisomic for chromosome I. This could be shown by means of electrophoretic karyotyping of the hybrid and of the four single-spore cultures from one ascus of the hybrid.