Rapid genetic test for discrimination between haploid and polyploid transformants in Saccharomyces.

Spheroplast fusion induced by polyethylene glycol often occurs during transformation of yeast spheroplasts. It leads to the appearance of polyploid transformants. We have developed a method of discriminating between haploid and polyploid transformants, based on qualitative comparison of the frequency of mitotic homozygotization for a recessive marker, lys2, in diploid and polyploid hybrids of transformants crossed with a tester haploid bearing lys2.We have used this method to compare the frequency of appearance of polyploids during transformations of spheroplasts and of intact cells using lithium chloride in the strain DC5. Polyploids constitute from 15% to 74% of transformants after transformation of spheroplasts. In lithium chloride transformation polyploids arose in only one of four experiments and constituted 9% of transformants.