3. (15 pts total) You plan to perform an Ames Test using a histidine auxotroph w

Question

3. (15 pts total) You plan to perform an Ames Test using a histidine auxotroph with a missense mutation called hisG. Below are three experiments (E1-E3) that you will perform plus a control sample (in parentheses) to compare it with. Choose one of the results (A, B, or C) you predict for the experiment compared to the control (2 pts each). PLUS, explain why you predict this result (3 pts each). A. Fewer colonies B. Same number of colonies C. More colonies EI: A mismatch-causing mutagen (versus a water control) . Explain why: Explain why: E2: A frameshift-causing mutagen (versus a water control) cells control) hisG cells that also have a DNA methyltransferase null mutation (versus a his Explain why: E3:

Explanation / Answer

E1: Since the mutants cells harbor a mismatch mutation, if they are treated with a mutagen that causes only mismatch mutation, there is a high chance that revertants may arise. So, we can find MORE COLONIES.

E2. A frameshift causing mutagen may cause a mutation at another locus (other than His) and trans-complement the mutant phenotype. So, we can observe the same number of colonies.

E3: DNA methyltransferase is a major enzyme involved in DNA mismatch repair. If it is mutated, there is less likely chance that revertants can arise. So, we can observe FEWER COLONIES.

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