Bodyweight QTL on mouse chromosomes 4 and 11 by selective genotyping: regression v. maximum likelihood

Two quantitative trait loci (QTL) for mouse bodyweight have previously been reported on mouse chromosomes (MMU) 4 and 11 from crosses of a highly fecund and large mouse strain, Inbred Quackenbush-Swiss 5 (QSi5) and C57B1/6J. QSi5 has now been crossed with CBA/CaH to produce 1128 F-2 mice to confirm the existence and effect of these QTL. In total, 226 mice from the upper and lower deciles for bodyweight were genotyped using 12 microsatellite markers covering MMU4 and MMU11. Regression and maximum likelihood based interval mapping by either including all mice (ungenotyped mice were treated as having missing genotypes) or including only selectively genotyped mice in the analyses were used to estimate the positions and effects of the QTL. The results confirmed the existence and effects of both QTL. Although all methods estimated the same QTL positions, the QTL effects were overestimated compared with the estimates using a suggested method (maximum likelihood by including all mice in the analysis). However, the overestimated QTL effects could be mathematically corrected. Since the confidence intervals of both QTL are still too large for positional cloning, an advanced intercross line is being bred for finely mapping these bodyweight QTL.