The yeast Saccharomyces cerevisiae can grow as haploid or diploid cells.

The yeast Saccharomyces cerevisiae can grow as haploid or diploid cells. You have two haploid yeast strains that each carry recessive mutations that affect regulation of the genes required for galactose metabolism. One strain has a deletion of the region of the genome on chromosome II that lies between the GAL1 and GAL10 genes (DUAS). The other strain carries a mutant allele of the GAL80 gene on chromosome XIII that produces no functional GAL80 protein.

(a) You cross these two strains together to get diploid progeny. Will expression of the GAL1 and GAL10genes in the progeny be permanently repressed, inducible in the presence of galactose, or constitutive (permanently expressed)? Why?

(b) You then induce meiosis to produce haploid progeny. What proportion of the haploid progeny will show silenced, inducible, or constitutive expression of GAL1 and GAL10?

You repeat the experiment described above, but instead of the GAL80- mutant you cross a GAL7- mutant strain to the DUAS strain (the GAL7 gene is also located on chromosome II, 5 kb away from the GAL1/GAL10 UAS sequences). Will expression of the GAL1 and GAL10 genes in the progeny be permanently repressed, inducible in the presence of galactose, or constitutive (permanently expressed)? Why?

You again induce meiosis to produce haploid progeny. In yeast, the rate of recombination is 2.5 kb/cM. What proportion of the haploid progeny will be able to grow on media where galactose is the only source of energy?