Chapter 12, Problem 37P

In an experiment employing the methods of the Ames test, two ${\text{his}}^{\text{-}}$ strains of Salmonella are used. Strain A contains a base substitution mutation, and Strain B contains a frameshift mutation. Four plates are prepared to test the mutagenicity of the compound ethyl methanesulfonate (EMS). Plate $\text{1}$ is a control plate with Strain A and $\text{S9}$ extract but no EMS. Plate $2$ is also a control plate and contains Strain B and $\text{S9}$ extract but no EMS. Plate $\text{3}$ contains Strain A along with $\text{S9}$ extract and EMS, and Plate $\text{4}$ contains Strain B, $\text{S9}$ extract, and EMS.

a. Characterize the expected distribution of colony growth on the four plates. Defend your growth prediction for each plate.

b. What event is being detected by growth of a colony on any of the four plates?

c. Why is the $\text{S9}$ extract added to each of the plates?

d. Suppose the compound being tested was proflavin instead of EMS. Would this change the Ames test results? Explain why or why not.