1. Describe one advantage and one disadvantage of doing a mutant screen in a sim
ID: 52308 • Letter: 1
Question
1. Describe one advantage and one disadvantage of doing a mutant screen in a simple monoploid organism like haploid yeast.
2. For the following yeast strains describe what nutrient supplements would be required for growth on a minimal medium. a. MATa ura3 leu2 b. MAT his4 leu1 c. MATa/ ura3/URA3 his4/HIS4 leu1/LEU1 leu2/LEU2 d. MATa/ ura3/URA3 his4/HIS4 leu1/leu1
3. You have isolated a new recessive tryptophan-requiring mutation in a MAT yeast strain. You cross this mutant to a MATa trp4 trp5 strain. What can you conclude if the diploid requires tryptophan for growth? What can you conclude if the diploid does not require tryptophan for growth?
4. In reference to the yeast mutant screen being done in class, it is common to find sectored colonies that are half or one-quarter mutant and the remaining portion being wild type. (The drawing below represents an example of this with black being growth and white begin no growth.) Assuming these types of colonies are derived from a single haploid cell give an explanation of how this might occur. (Hint - think in terms of mutagenesis, DNA replication, and DNA repair.)
5. Mutations in the ADE2 gene result in the buildup of a red pigment derived from 5’-phosphoribosyl-5-aminoimidizole. Mutations in the ADE6 gene do not turn red. If you created an ade2 ade6 double mutant yeast strain, what color would you expect it be. (The pathway diagram on page 4 of the Yeast Mutagenesis handout may be helpful.)
6. In past years in BI 513, ade2 mutants were found that turned pink, but could still grow without an adenine supplement. Propose an explanation for how this could be. (Assume that the assignment of the mutation to ADE2 is correct.)
Explanation / Answer
1. Advantages:
Haploid cells easily express the mutant phenotype though the mutation is recessive.
Easy identification of the mutant gene is possible.
Disadvantages:
It is difficult to perform the analysis though a recessive mutation is lethal.
3. If the mutant requires tryptophan:
The other strain also has a mutation in the trp gene.
The trp gene in the other strain is non-functional.
The mutation is dominant.
If the mutant does not requires tryptophan:
The mutation is recessive.
5. The resulting mutants would express pale red color colonies.
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