Auxotrophic mutants have been induced by UV-irradiation and EMS treatment in meiotic segregants of a distiller's production strain of yeast, In complementation tests some of the mutants were allelic to adel, ade3, lys2, met13, trpl, ural and ura4 of standard strains orS. cerevisiae.Crosses were made between two spore-derived clones of the distiller's strain and haploid S. cerevisiae strains carrying several auxotrophic markers. Tetrad analysis of the mating products revealed that the spore-derived clones were disomic for six and seven chromosomes, respectively.Chromosomes III from the distiller's production strain were compared to their counterparts in standard strains ofS. cerevisiae at several loci. Cloned DNA from HIS4, LEU2 and MATloci from the standard strain were used as hybridization probes to test the nucleotide sequence homology at these loci and the silent mating type genes HAIL and HMR. Restriction site polymorphisms were not detected inside the loci but in regions adjacent to them. These could be exploited in combination with tetrad analysis to identify four different chromosomes III in the distiller's strain. Of the four chromosomes, three were lacking HML and one was lacking HMR. The data are consistent with the assumption that all loci tested are organized in the same order as in the genetically analysed standard strains.

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