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

Question

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.

A. Will these diploid cells be able to grow on media where galactose is the only source of energy?

B. 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.

Explanation / Answer

A) These diploid cells can grow in the presence of galactose

Strain A has no GAL1 and GAL10 but has GAL2 protein and Strain 2 has no GAL2 but has GAL1 and GAL10 genes. When these two haploids were crossed, we will get a diploid with functional GAL1, GAL10 and GAL2 genes. Thus, they can survive in only galactose media.

B) Yes, haploid progeny can grow in the presence of galactose only media.

Because during meiosis, recombination/crossing over events occur, which can result in the formation of haploid with functional GAL1, GAL10 and GAL2 proteins.

For example if crossing over occurs between the sequence between chromosome GAL1 and GAL10 of Strain A to sequence between GAL1 and GAL10 of strain B. The resulting haploid will have functional GAL1 and GAL10 proteins along with functional GAL2. Thus the haploid can grow in the presence of galactose only media

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