High frequency of a lethal gene (te) in a laboratory stock of mice

Abstract

A long-established laboratory stock was found to contain many individuals that were heterozygous for a lethal gene, called tailless-Edinburgh (te). Heterozygotes are indistinguishable from normals except by breeding tests with special tester stocks supplying brachyury (T) gametes, when tailless (Tte) progeny distinguish carrier parents from normal parents that produce only short-tailed (T +) progeny. When males are mated to tester females providing brachyury eggs, the ratio of Tte: T + progeny reflects the ratio of te: + spermatozoa. The proportion of te spermatozoa measured in this way led to the expectation that 62% of individuals in the original stock would be carriers, whereas 80% was found. Independent evidence is presented for + te males that the incidence of te in their effective spermatozoa was higher when normal eggs were fertilized in matings within the original stock than when brachyury eggs were fertilized in outcross matings to the tester stock. These observations suggest that the proportion of te spermatozoa partaking in fertilization was modified by the genotypes of the females or of their eggs.