Why Is An Ames Test Sometimes Called A Reverse Mutation Assay?

Why Is An Ames Test Sometimes Called A Reverse Mutation Assay? This is to say that when a mutagenic event occurs, base substitutions or frameshifts within the gene can cause a reversion to amino acid prototrophy. This is the reverse mutation. Why is the Ames test considered a reversion test? Induction of new mutations replacing