Genetics Question

Question 1: (6 points)

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 (deltaUAS). The other strain carries a mutant allele of the GAL80 gene on chromosome XIII that produces no functional GAL80 protein.

 

(a) Which of the following correctly describe GAL80?

(a) GAL80 is a transcriptional activator.
(b) GAL80 is a trans-acting factor in the regulation of the GAL structural proteins.
(c) GAL80 is allosterically regulated by galactose.
(d) GAL80 masks the activation domain of GAL4.
(e) GAL80 is an enzyme involved in the catabolism of galactose.

 

(b) Which of the following correctly describe UAS?

(a) UAS is a cis-acting regulatory DNA sequence.
(b) UAS is bound by the DNA-binding domain of GAL4.
(c) UAS is a trans-acting factor that silences GAL gene expression.
(d) UAS is allosterically regulated by binding galactose.
(e) UAS is used in the enhancer of multiple GAL genes to result in coordinated induction.

 

(c) You cross these two strains together to get diploid progeny. Write down the diploid genotype.  Expression of the GAL1 and GAL10 genes in the progeny will be

__________

 

You then induce meiosis to produce haploid progeny. Write down the haploid progeny genotypes.

 

(d) What proportion of the haploid progeny (expressed as a decimal) will have permanently repressed expression of GAL1 and GAL10?  ____________

 

(e) What proportion of the haploid progeny (expressed as a decimal) will have inducible expression of GAL1 and GAL10 in the presence of galactose?  ____________

 

(f) What proportion of the haploid progeny (expressed as a decimal) will have contstitutive expression of GAL1 and GAL10?   ____________

 

 

Genetics Question 2:

(6 points)

You repeat the experiment described in the previous question, but instead of the GAL80- mutant you cross a GAL7- mutant strain that produces no functional GAL7 protein to the deltaUAS strain. The GAL7 gene is also located on chromosome II, 5 kb away from the GAL1/GAL10 UAS sequences.

 

(a) Which of the following correctly describe GAL7?

(a) GAL7 is a transcriptional activator.
(b) GAL7 is a trans-acting factor in the regulation of the GAL structural proteins.
(c) GAL7 is allosterically regulated by galactose.
(d) GAL7 is a cis-acting enhancer element that promotes coordintated induction of the GAL genes.
(e) GAL7 is an enzyme involved in the catabolism of galactose.

 

(b) You cross these two strains together to get diploid progeny. Write down the diploid genotype.  Expression of the GAL1 and GAL10 genes in the progeny will be 

__________

 

(c) You again induce meiosis to produce haploid progeny. In yeast, the rate of recombination is 2.5 kb/cM. Write down the progeny genotypes. What proportion of the haploid progeny (expressed as a decimal) will be able to grow on media where galactose is the only source of energy?  ____________ 

 

(d) Which of the following haploid genotypes can grow on media where galactose is the only source of energy?

(a) deltaUAS, GAL7+
(b) deltaUAS, GAL7
(c) UAS+, GAL7+
(d) UAS+, GAL7

Genetics Question 3:

(3 points)

Use the model below of the Drosophila sex determination regulatory cascade to answer the following questions about how mutations in genes in this pathway will affect the expression of sex.

 

 

 

 

 

 

 

 

What would you predict to be the somatic sexual phenotype (female or male) of a Drosophila fruit fly that carries the following mutations?

(a) homozygous for a deletion mutation that removes the Sex-lethal gene

Female

[  ]

Male

[  ]

 

 

b) homozygous for a deletion mutation that removes the Transformer gene

Female

[  ]

Male

[ ]

c) homozygous for a mutation in the Transformer gene that removes the 5′ (upstream) stop codon.

Female

[  ]

Male

[ ]

 

 

 

 

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