STREPTOMYCIN RESISTANCE: A GENETICALLY RECESSIVE MUTATION

Abstract

Diploid cultures of Escherichia coli, strain K-12, were isolated from crosses of distinct auxotrophic mutants plated on minimal agar. Cultures heterozygous for streptomycin resistance (Sr/Ss) were recovered from crosses of parents differing in this character. Ss was found to be dominant over Sr, i.e., heterozygous cells were inhibited from forming colonies at the same levels of streptomycin as inhibited ordinary Ss haploids, although in the absence of streptomycin the heterozygotes repeatedly threw Sr haploid segregants.