Chapter 11, Problem 28P

In an Ames test using ${\text{his}}^{\text{-}}$ Salmonella bacteria a researcher determines that adding a test compound plus the $\text{S9}$ extract produces a large number of ${\text{his}}^{\text{+}}$ revertants, but mixing the ${\text{his}}^{\text{-}}$ strain plus the test compound without adding $\text{S9}$ does not produces an elevated number of ${\text{his}}^{\text{+}}$ revertants.

a. What is the reason for the different experimental results described?

b. Is the test compound still considered to be a potential mutagen? Explain why or why not.