Comparative Frequency of Dominant and Recessive Markers for Drug Resistance in Chinese Hamster Cells

Summary

Resistance to vinblastine sulfate (VEL) is expressed as a dominant characteristic in Chinese hamster cells, whereas resistance to cytosine arabinoside (ara-C) is recessive. A differential in the expression of these markers would accordingly be expected at the phenotypic level. Direct determinations showed that the background incidence of spontaneous resistance to VEL was similar to that for ara-C in both diploid and tetraploid cell populations. Exposure to nitrosoguanidine (MNNG) increased the incidence of both VEL and ara-C resistance, and the doseresponse curves obtained with rising concentrations of mutagen were coincident or parallel, irrespective of ploidy level. The expression of spontaneous or induced variation thus seemed independent of the dominant or recessive nature of the markers studied. These findings suggest that resistance to VEL and to ara-C may arise by nonchromosomal changes.