HG11
In the original intercross CAST alleles near 50 cM on MMU11 were linked with a reduction in G29, carcass ash (ASH) and carcass protein (PROT) [24]. Therefore, we measured each carcass component using chemical compositional analysis in the HGC, HG11 and HG17 strains. Originally, Carp2 was dependent on the presence of hg and no significant sex effects were detected [24]. In contrast to those results, HG11 mice displayed significant differences in growth and obesity between the sexes. In general, males demonstrated a 5% increase and females a 5% decrease in all growth-related traits (Table 4). Most of these differences, however, were not significant at a critical P < 0.005, although almost all were at a nominal P < 0.05. Following the same trend, males displayed an increase in tail length and a small suggestive increase in NA (P = 0.06), while females displayed significant decreases in NA. In support of the sex-specific QTL effects strain by sex interactions (P < 0.04) were seen for the following growth traits: 3WK, 6WK, 9WK, G26, G29 and NA (data not shown). The basis of each interaction was an increase in the males and a decrease in females.
In our analysis of the HGC, HG11 and HG17 strains, concordant results were observed measuring adiposity using chemical lipid extraction and weighing fat pad mass. The phenotypic correlation between carcass fat (FAT) as a percent of the empty carcass weight (ECW; weight of total body (including organs) minus the head and gastrointestinal tract) (%FAT) determined by chemical analysis and AI, using data from all three lines (HGC, HG11 and HG17), was 0.92. These data suggest that individual fat pad dissection is an excellent proxy for measuring whole body adiposity and provides a much more sensitive technique to measure fat accumulation in specific body regions.
HG11 females displayed slight increases in all fat pads (except MFP) and AI, although, only the 16.5% increase in AI was significant (Table 5). In contrast, HG11 males did not show a difference in fat mass leading to a significant strain by sex interaction (P = 0.008) for AI (data not shown). Identical to the results obtained using fat pad weights; female HG11 carcasses displayed an increase in %FAT (Table 6).
HG11 male carcasses had higher levels carcass ash (ASH) as a percent of ECW (%ASH) and female carcasses displayed lower levels of H2O and ASH (Table 6). Strains by sex interactions (P < 0.005) were identified for H2O, %H2O, %FAT, ASH and PROT (data not shown). If the aggregate phenotype in HG11 is due to a single locus, its function may be to disrupt energy partitioning by decreasing the deposition of lean tissue and increasing lipid accumulation in females, while having the opposite action in males. However, it may also be due to distinct sex-specific QTL with opposing action.