Ploidy of a mutant Saccharomyces cerevisiae defective in homologous recombination

The ploidy of a mutant of Saccharomyces cerevisiae defective in recombination (Rec-) has been determined using tetrad analysis and flowing fluorometry. Evidence is obtained that the effect of the Rec- phenotype, i.e. the increase of the stability of plasmids with 2 mkm DNA ori replication in the yeast cirO cells is not the result of the diploidy in cells of the Rec- mutant developed in the process of transformation.