Quantitative trait loci affecting growth in high growth (hg) mice

A genome-wide scan was performed in order to identify Quantitative Trait Lo ci (QTL) associated with growth in a population segregating high growth (hg ), a partially recessive mutation that enhances growth rate and body size i n the mouse. A sample of 262 hg/hg mice was selected from a C57BL/6J-hg/hg X CAST/EiJ F-2 cross and typed with 79 SSLP markers distributed across the genome. Eight significant loci were identified through interval mapping. Lo ci on Chromosomes (Chrs) 2 and 8 affected the growth rate of F-2 mice. Loci on Chr 2 and 11 affected growth rate and carcass lean mass (protein and as h). A locus on Chr 9 modified femur length and another one in Chr 17 affect ed both carcass lean mass and femur length, but none of these had significa nt effects on growth rate. Loci on Chrs 5 and 9 modified carcass fat conten t. Additive effects were positive for C57BL/6J alleles, except for the two loci affecting carcass fatness. Typing of selected markers in 274 +/+ F-2 m ice revealed significant interactions between hg and other growth QTL, whic h were detected as changes in gene action (additive or dominant) and in all ele substitution effects. Knowledge about interactions between loci, especi ally when major genes are involved, will help in the identification of posi tional candidate genes and in the understanding of the complex genetic regu lation of growth rate and body size in mammals.