[Non-Mendelian inheritance of the Un(s) mutant gene in mice]

The phenotypic expression of the mutation Uns (gene Pax-1) were studied in the progeny of heterozygous mice. In all crosses, the sex ratio close to 1:1 was observed in the progeny. However, among sons and daughters the segregation for the mutant character depended on the variant of the cross variant. When the Uns/+ mice were intercrossed, the ratio of mutant to normal females was 3:1, while the corresponding ratio among males was 0.9:1. Studying preimplantation development in vitro and postimplantation development in vivo revealed no significant mortality in embryos obtained by crossing heterozygous mice. Ultrastructural analysis revealed no distortions in synapsis and desynapsis of axial elements of the autosomal chromosomes in Uns/+ mice. The segregation found seems to result either from different fertilizing ability of normal sperm and sperm carrying the Uns mutation or, which is more probable, from the genetic imprinting of the gene Uns.