Evidence of a large sex-linked effect accounting for 25% of the
divergence between mouse lines
selected for body weight has been described previously. A marker-based
study
was undertaken to
determine the number and map positions of the putative X-linked quantitative
trait loci (QTLs).
An F2 population was generated from a reciprocal F1
between an inbred low line derived from the
low selection line and the high selection line. To enable inference of
marker-associated QTL effects
on the X chromosome, an analytical technique was developed based on
the multiple 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 of 24·4. The likelihood curve showed a single well-defined
peak, and gave a 95% confidence
interval for the QTL location of 8 cM. The estimates for the additive
genotypic effects in males
and females (half the differences between hemizygous males and between
homozygous females)
were 2·6 g in both cases, or 17% and 20% of the 10 week body weight
in
males and females
respectively. Dominance effects in the females were found to be non-significant.
No significant X-linked effect on carcass fat percentage was detected,
but
a single X-linked QTL appears to explain
almost the entire X-linked body weight effect.
Mapping quantitative trait loci for body weight on the X
chromosome in mice. I. Analysis of a reciprocal F2 population
