X-RAY-INDUCED MUTATION TO 6-THIOGUANINE RESISTANCE IN CULTURED HUMAN DIPLOID FIBROBLASTS

X-ray induced mutation to 6-thioguanine (6TG)-resistance was studied in early passage cultures of human diploid fibroblasts. The appearance of phenotypic induced mutants in irradiated cell populations was linearly related to the number of post-irradiation cell doublings and to the duration of the growth period prior to mutant selection; the maximum yield of X-ray induced mutants was observed when cells surviving radiation had completed 3-4 doublings (6-7 days growth) in non-selective medium. The maximum induced mutation frequency was linearly related to X-ray dose and the mutation rate was estimated to be 3.1 .cntdot. 10-7 mutations/viable cell per rad. X-ray induced mutations in cultured human diploid fibroblasts were compared with established cell cultures and with theoretical predictions of X-ray mutation rates in human germ cells.