Sex-of-offspring-specific transmission ratio distortion on mouse chromosome X

During our study of the DDK syndrome, we observed sex ratio distortion in f avor of males among the offspring of Fl backcrosses between the C57BL/6 and DDE; strains. We also observed significant and rf producible transmission ratio distortion in favor of the inheritance of DDK alleles at loci on chro mosome Xamong female offspring but not among male offspring in (C57BL/6 X D DK) F-1 X C57BL/6 and (C57BL/ 6-Pgk 1(a) x DDK) F-1 X C57BL/6 backcrosses. The observed transmission ratio distortion is maximum at DXMit210 in the ce ntral region of chromosome X and decreases progressively at proximal and di stal loci, in a manner consistent with the predictions of a single distorte d locus model. DXMit210 is closely linked to two distortion-controlling loc i (Dcsx1 and Dcsx2) described previously in interspecific backcrosses. Our analysis suggests that the female-offspring-specific transmission ratio dis tortion we observe is likely to be the result of the death of embryos of pa rticular genotypic combinations. In addition, we confirm the previous sugge stion that the transmission ratio distortion observed on chromosome X in in terspecific back-crosses is also the result of loss of embryos.