A Third Lethal in the T (Brachy) Series in the House Mouse

Abstract

Congenital absence of the tail in a strain of mice first isolated by Do-brovolskaia-Zawadskaia and Kobozieff (1932) has been shown (Chesley and Dunn, 1936) to be due to interaction between the dominant gene for Brachyury T (Dobrovolskaia-Zawadskaia, et al., 1934; Chesley 1935) and a recessive allele I. This strain, known as Line A, breeds true to tailless-ness because of a balanced lethal condition. The genetic composition of tailless animals of this line is TDI; the homozygotes TT die at 10-11 days after fertilization; t°t° embryos die shortly after implantation (6th-7th day) and only the compounds Tto survive. T and to show no crossing-over and are probably alleles. In a second tailless line,' also isolated by Dobrovolskaia-Zawadskaia and Kobozieff (1932) and designated as Line 29, a similar situation has now been found. Data in support of this statement are given in table 1. The strain breeds true to taillessness and produces small litters (Exp. 1). Crosses of tailless animals from this line by normal-tailed animals produced normal and short-tailed (Brachy) progeny (Exp. 2), indicating that Line-29 tailless is heterozygous for Brachyury (T). As in crosses of Line-A tailless, the ratios from Line-29 tailless females approximate 1 normal: 1 Brachy; those from tailless males indicate a marked excess of normals (Exp. 3). All F, normals when tested by Brachy (T+) transmitted taillessness, 474 PROC. N. A. S.