Hybridization and cytoduction among yeast cells of the same mating type

Summary Use of a selective system for cytoduction in Saccharomyces cerevisiae allowed us to monitor hybrid formation and to clone the haploid nuclei of cells which have participated in illegitimate matings: a × a, × . Our approach has made it possible to select nuclei with mating-type switches and mutations within the MAT locus. It was shown that matings in × crosses often proceed through nonheritable genetic changes located within chromosome III. We suggest that these non-heritable genetic changes are due to premutational lesions, expressed phenotypically as transient -matingtype. After a mating event these lesions are either repaired or converted to true mutations within the MAT locus.