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

Abstract

SummaryMatings between mice bearing the dominant deletionThpand mice segregating for thetw73haplotype failed to produce the expected viable tailless (Thp/tw73) progeny. Histological analysis of litters fromThp/ + × + /tw73matings revealed an abnormal class of embryos which failed to implant normally between days 6·5 and 7·5 of gestation, and were indistinguishable fromtw73/tw73homozygotes.Thphomozygotes 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 thetw73implantation defect maps within theThpdeletion. Sincetw73is viable with another deletion,Torl, thetw73defect must occur in the region of non-overlap betweenThpandTOrl. The possibility that thetw73-associated implantation defect is a parasitic lethal mutation (p), mapping to the proximal part of thetw73chromosome, is discussed.