You are screening three new pesticides for potential mutagenicity using the Ames test. Two his- strains resulting from either a frameshift or a transition mutation were used and produced the following results (number of revertant colonies): Strain 1
Transition Mutant Control (no chemical) Transition Mutant + Chemical Transition Mutant + Chemical + Rat Liver Enzymes
Pesticide#1 21 180 19
Pesticide#2 18 19 17
Pesticide#3 25 265 270
Strain 2 Framshift Mutant Control (no chemical) Framshift Mutant + Chemical Framshift Mutant + Chemical + Rat Liver Enzymes
Pesticide#1 5 4 5
Pesticide#2 7 5 93
Pesticide#3 6 9 7

Required:
What type of mutations, if any, do the three pesticides induce?

- Pesticide 1: Induces transition mutations. Rat liver enzymes convert it into a nonmutagenic product. Does not induce frameshift mutations.

- Pesticide 2: Does not induce transition mutations. Rat liver enzymes convert it into frameshift mutagen.  

- Pesticide 3: Induces transition mutations. Rat liver enzymes don't have ability to convert compounds into mutagens. Does not induce frameshift mutations.

Explanation:

The Ames test is a technique widely used to evaluate the mutagenic potential of a particular chemical compound. The Ames test uses Salmonella typhimurium strains with a defective mutation that makes them unable to synthesize histidine. When the mutation is reversed, then the revertant strains can grow on a medium lacking histidine. A positive test shows that the chemical is mutagenic because its activity is associated with the reversed mutation and thereby the mutant gene regains its function. In humans, as well as in other mammals, many chemicals don't have mutagenic effects themselves but they may become converted into mutagens when are metabolized by the body. For that reason, rat liver enzymes are added to replicate the metabolic effects of the chemical compound being tested. Nowadays, current tests can express recombinant human proteins instead of rat liver enzymes, thereby enabling a better correlation between mutagenic activity and human metabolic processes.

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