The yeast Saccharomyces cerevisiae can grow as haploid or di

The yeast Saccharomyces cerevisiae can grow as haploid or diploid cells. You have two haploid yeast strains that each carry mutations that make them unable to grow when galactose is the sole available source of energy. One strain has a deletion of the entire region of the genome between the GAL1 and GAL10 genes (DUAS). The other strain carries a mutant allele of GAL2 that produces no functional GAL2 protein. You cross these two strains together to get diploid progeny. Will these diploid cells be able to grow on media where galactose is the only source of energy?

You then induce meiosis to produce haploid progeny. Will any of the haploid progeny be able to grow on media where galactose is the only source of energy? Explain.

Solution

GAL2 protein is non-essential i.e. the mutant not having GAL2 will survive in normal concentration of galactose but will not grow in low concentration of galactose. So the diploid will have all genes except truncated Gal2 and will grow in good concentration of galactose and the haploid progeny will never get a functional Gal 2 but those containing rest of the Gal genes (DUAS) will survive in media containing only Galactose in good concentration.