“Bent-Tail,” A Dominant, Sex-Linked Mutation in the Mouse

Abstract

A single Bent-tail (Bn) male in a litter of 7 from a mating between a normal Namru strain female and a bald (hrba) male was used in genetic tests for Bn. The expression of Bn in Bn/bn females was more variable than in Bent-tail males and ranged from a single, very slight bend to extreme cases in which the tail was curled and pressed against the body. Penetrance in females was at least 95% and in males 100%. Tail length was normal in heterozygous females but approx. half length in Bent-tail males and in Bn/Bn females. Bn/bn females did not differ from normal females in rate of growth, but approx. 50% of Bent-tail males and all Bn/Bn females were smaller at birth and matured more slowly than normal mice. Genetic tests indicated that Bent-tail was a dominant, sex-linked mutation and that Bent-tail males were homozygous (Bn/O), with Bn located in the non-homologous segment of the X-chromosome. A significant deviation between observed and theoretical ratios in litters from ma tings between Bn/bn females and Bent-tail males, with the normal class comprising 50% of the population, was ascribed to a lethal effect of Bent-tail in the male or homozygous female. The mean litter size for different types of matings indicated that Bn/bn females were less fertile than bn/bn females, and Bn/Bn females less fertile than Bn/bn females.