Isolation of monosomics in yeast.

Tetraploid cultures of Saccharomyces cerevisiae triplex (A/A/A/a) at several loci were sporulated. All the diploid spores are expected to be homozygous (A/A) or heterozygous (A/a) and, hence, to have the dominant phenotype. Cells lacking one of the chromosomes (monosomics) may show the recessive phenotype (a/-). Therefore, spores that grew on complete medium but failed to grow on the relevant synthetic single-omission media were presumed to be monosomic. These isolates were further characterized by sporulation, and several stable monosomics were established.