The effect of ploidy on chemical mutagenesis in cultured chinese hamster cells

Abstract The frequency of mutations induced by ethyl methane sulfonate was compared in a pseudodiploid Chinese hamster cell strain and in a tetraploid substrain derived from it. The frequency of reverse mutations from glycine auxotrophy to glycine independence was similar in the two strains, as expected for a dominant phenotype. Forward mutation to 6‐thioguanine‐resistance was 25 fold lower in the tetraploid as compared to the diploid strain. The resistant mutants lack hypoxanthine phosphoribosyl transferase activity and their resistant phenotype is recessive in somatic cell hybrids. A combination of chromosomal segregation and mutation could account for the frequency of these recessive drug‐resistant mutants in the tetraploid population.