1. In this Ames test, we used S. typhimurium strain TA 1535 which has a base pai
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Question
1.In this Ames test, we used S. typhimurium strain TA 1535 which has a base pair substitution in the hisG gene making the cells auxotrophic for histidine. Would this strain be useful in detecting frameshift mutations induced by a test compound? Why or why not?
2.Can you think of any test substances that might give a false positive result on an Ames test plate?
3.In the Ames test, a few colonies may appear on the negative control plate (with no potential mutagen added). Why is this?
Explanation / Answer
1. Yes. The organism that has either a frameshift mutation or a point mutation could be used to identify the carcinogen. This is because the carcinogens could act either by replacing a GC by an AT in the gene sequence (point mutation), or it would act by adding or deleting a single base pair (frameshift mutation).
2. Yes. A compound that is capable of inducing genotoxic mode of action could induce a frameshift mutation or a point mutation reverting the autoxotrophs back to their wild form, even though they are not potential carcinogens.
3. This could be because of the natural revertion through spontaneous mutation. Organisms during their multiplication are capable of undergo mutation. But the ratio of mutation is very minimal that one in a million or a trillion cells would undergo natural mutation. If such a mutation occurs in the histidine gene, there is a chance for the reversion of the auxotrophic strains to the wild strains.
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