In addition to the large number of MMU2 QTL, the presence of hg adds complexity by either eliciting interactions with the same QTL or by inducing the expression of novel QTL. The 2P unique region (Region I) contains an hg modifier with large effects on growth and smaller effects on obesity (Table 3). In contrast, interactions between 2PM/2M QTL and hg primarily affect fat deposition (Table 3). As illustrated in Figure 4 the 2M donor region exhibits strong sex effects on the rate of lipid storage, dependent on background. In control mice, HGC females have a higher AI than males, while the opposite is seen in B6C mice. Interestingly, the 2M hg modifier QTL abolished the hg induced sexual dimorphism in adiposity (Figure 4). Although these results provide insight into the nature of hg modifier QTL, it should be noted, that the actual number and precise location of loci is still unclear.