title: Fluctuation analyses of spontaneous mutations to 6-thioguanine resistance in Chinese hamster ovary cells in culture.
abstract: Fluctuation analyses of the spontaneous appearance of 6-thioguanine (TG)-resistant mutants in cultured Chinese hamster ovary (CHO) cells were performed to investigate (1) whether the resistance is induced by the selective agent or is the result of a mutation which occurs prior to the TG selection and (2) to estimate the spontaneous mutation rate at the hypoxanthine--guanine phosphoribosyl transferase (hgprt) locus. The potential problem of phenotypic delay was minimized by allowing an adequate expression time through maintenance of the cultures in a division-arrested, viable state. The results demonstrate that the TG-resistant (TGr) cells arise randomly in the cultures, independently of the selective agent, which is consistent with spontaneous mutations. The average values for mutation rate +/- standard deviation, based on 4 independent determinations and 2 methods of calculation, are 3.4 +/- 1.2 X 10(-7) (median method) and 5.1 +/- 1.8 X 10(-7) (mean method) mutants/cell/generation.
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004351:Drug Resistance; D005260:Female; D005787:Gene Frequency; D008433:Mathematics; D009154:Mutation; D010053:Ovary; D013866:Thioguanine / Q000494:pharmacology*
chemical_list: D013866:Thioguanine