Rate of induced forward mutation at 3 genetic loci in Salmonella typhimurium

The rate of forward mutation to 8-azaguanine, 5-fluorouracil and azetidine carboxylic acid resistance was measured in Salmonella typhimurium following treatment with 18 chemical mutagens. Although the absolute frequency of both spontaneous and chemically-induced mutation was different at the markers scored, the 3 selection systems were found to be equisensitive: each system produced a statistically significant response at approximately the same mutagen concentration. This result suggests that in Salmonella the target size present in a given forward mutation assay is sufficiently large to approximate the level of mutation occurring elsewhere in the chromosome in sections of DNA of similar size.