Genetic analysis of thetw73haplotype of the mouse using deletion mutations: evidence for a parasitic lethal mutation

Abstract

Matings between mice bearing the dominant deletion Thp and mice segregating for the tw73 haplotype failed to produce the expected viable tailless (Thp/tw73) progeny. Histological analysis of litters from Thp / + × + /tw73 matings revealed an abnormal class of embryos which failed to implant normally between days 6·5 and 7·5 of gestation, and were indistinguishable from tw73/tw73 homozygotes. Thp homozygotes displayed a different lethal phenotype, failing to successfully make the transition from morula to blastocyst at day 3·5. These studies indicate that the mutation responsible for the tw73 implantation defect maps within the Thp deletion. Since tw73 is viable with another deletion, Torl, the tw73 defect must occur in the region of non-overlap between Thp and TOrl. The possibility that the tw73-associated implantation defect is a parasitic lethal mutation (p), mapping to the proximal part of the tw73 chromosome, is discussed.