Practice question

Ames test developed by Bruce Ames rapidly screens chemical mutagenicity using auxotrophic Salmonella typhimurium strains carrying defined his mutations requiring histidine for growth. Compound incubated with bacteria in presence of rat liver S9 microsomal fraction providing cytochrome P450 mediated metabolic activation converts promutagens to active metabolites. Mutagenic activity causes reversion to histidine prototrophy allowing colony growth on minimal plates, with revertant count proportional to mutagenic potency. Correlation with carcinogenicity established assay as frontline environmental genotoxin monitor. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.