In the Ames test, what types of mutations are used to test for chemical mutagens?

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The Ames test uses bacterial strains that carry specific mutations in the histidine biosynthesis pathway, such as hisS1 and hisG46. These mutations result in the inability of the bacteria to produce histidine, unless a mutation occurs that restores the function of the pathway. The test chemical is added to the bacteria and if it causes mutations that restore the function of the histidine pathway, the bacteria will be able to grow on a histidine-deficient medium, resulting in a positive result for mutagenicity. Therefore, the mutations tested for are his^- to his⁺.

In the Ames Test, What Types of Mutations Are Used