SELF-DIPLOIDIZATION IN SACCHAROMYCES-CEREVISIAE-KAR2 HETEROKARYONS

Zygotes isolated by micromanipulation from crosses of Saccharomyces ce revisiae strains, one of which carries a kar mutation, give rise most frequently to cytoductant colonies showing the nuclear constitution of either one of the two haploid parental strains. In crosses of kar2-1 strains to wild-type, about 10% of the cytoductants of both mating typ es are homozygous autodiploids. There is evidence indicating that self -diploidization occurs by fusion between sibling nuclei in the heterok aryotic zygote. Here we describe this phenomenon and propose to take a dvantage of it for the construction of genotypically-defined diploids able to mate, and of polyploid strains, which are useful tools in gene tic and cytological studies.