Widespread Distribution of Mutant Alleles (t-Alleles) in Populations of Wild House Mice

Abstract

FOLLOWING the proof that mutant changes at one locus (t) occur rather frequently in laboratory stocks of mice kept in the balanced lethal condition¹ T/tⁿ, we turned our attention to the problem whether such mutations are to be found also in wild populations. In the laboratory we had detected such mutations only in stocks which already contained a t-allele at this locus; stocks containing T (brachyury = short tail) had been under continuous observation in the laboratory since 1932, but no occurrence of mutation to a t-allele (revealed by the tailless condition T/tⁿ) had been detected. Seven different t-alleles were detected and isolated¹ by testing the rare normal-tailed exceptions which were found after inbreeding the balanced-lethal tailless stock T/t¹. All such exceptions proved to be t/t^x, t^x being a new allele at this locus. This suggested that t^x had arisen either by recombination or rearrangement at the complex locus t (Dunn, 1954) or that t¹ had induced mutation to a new allele. The fact that the new mutants were different from t¹ and from each other and that no recombination gametes containing the normal allele (+) were found was taken as evidence against the recombination hypothesis. The locus thus appeared to be unstable in the balanced lethal laboratory stocks. A question of interest was whether there was any evidence of this in wild populations remote from the few laboratories at which t-alleles were maintained.