MAPPING QUANTITATIVE TRAIT LOCI FOR BODY-WEIGHT ON THE X-CHROMOSOME IN MICE - I - ANALYSIS OF A RECIPROCAL F-2 POPULATION

Evidence of a large sex-linked effect accounting for 25% of the diverg ence between mouse lines selected for body weight has been described p reviously. A marker-based study was undertaken to determine the number and map positions of the putative X-linked quantitative trait loci (Q TLs). An F-2 population was generated from a reciprocal F-1 between an inbred low line derived from the low selection line and the high sele ction line. To enable inference of marker-associated QTL effects on th e X chromosome, an analytical technique was developed based on the mul tiple regression method of Haley and Knott. The analysis of data on 10 week weight indicated a single QTL of large effect situated at about 23 cM from the proximal end of the chromosome, with a peak LOD score o f 24.4. The likelihood curve showed a single well-defined peak, and ga ve a 95% confidence interval for the QTL location of 8 cM. The estimat es for the additive genotypic effects in males and females (half the d ifferences between hemizygous males and between homozygous females) we re 2.6 g in both cases, or 17% and 20% of the 10 week body weight in m ales and females respectively. Dominance effects in the females were f ound to be non-significant. No significant X-linked effect on carcass fat percentage was detected, but a single X-linked QTL appears to expl ain almost the entire X-linked body weight effect.