Segregation analysis of a sex ratio distortion locus in congenic mice

The congenic HG.CAST-(D17Mit196-D17Mit190) (HQ17(hg/hg)) mouse strain showed a significant departure on the expected 50%/50% offspring sex ratio in more than 2400 progeny (55.7% females). The entire pedigree file included data from 13 nonoverlapping purebred generations and an F-2 cross with the C57BL/6J inbred strain. Offspring sex ratio data were analyzed on the basis of 40 purebred HQ17(hg/hg) sires and 29 F-1 HQ17(hg/hg) x B6 sires under a Bayesian Binomial segregation model accounting for 4 different autosomal inheritance models of gene action (i.e., additive, dominance, recessive, and overdominance) and X-linked and Y-linked loci. For each model, the segregation effect was evaluated as a single regression coefficient for all sires or assuming 2 independent regression coefficients accounting for offspring sex ratio departures in purebred and F-1 sires, respectively. The deviance information criterion clearly favored the autosomal dominance model with different regression coefficients for the 2 groups of sires. Under this model, the dominance effect increased the percentage of female offspring by 4.3% (HQ17(hg/hg) purebred sires) and 8.2% (F-1 sires) with the highest posterior density regions ranging from 0.5% to 10.6% and from 1.3% to 14.4%, respectively. This article provides significant evidence of genetic determinism for sex ratio distortion in the HQ17(hg/hg) strain and develops new analytical tools to perform segregation studies on dichotomous traits.