Identification of multiple quantitative trait loci affecting the size and shape of the mandible in mice.

A quantitative trait locus (QTL) analysis was performed on the size and shape of the mandible in F(2) mice between KK-A ( y ) and C57BL/6 J strains and the effect of the A ( y ) allele on the morphology of the mandible was analyzed. A total of 13 measurements were taken on each right mandible. By means of discriminant and canonical discriminant analyses, KK-A ( y ) males and KK males were exactly discriminated from each other. In contrast to its known effects on body weight, the A ( y ) allele reduced the overall size of the mandible. QTL analysis of the 13 measurements and on three principal components extracted from these measurements identified multiple QTLs. When F(2) a/a and F(2) A ( y )/a were analyzed separately, 11 significant main-effect QTLs were identified in F(2) a/a, whereas only two QTLs were identified in F(2) A ( y )/a. Although four significant interactions were identified, all were in F(2) a/a. The A ( y ) allele thus made the difference in the size and shape of the mandible between strains obscure. Among mandible QTLs, those on Chrs 5 (Mssq6 and Mssq7) and 15 (Mssq14) were important. Mssq6 had an effect on the height of the posterior mandible. Mssq7 had an effect on mandible length. Mssq14 had an effect on the height of the anterior and posterior mandible. Mssq7 and Mssq14 also had an effect on the overall size. Thus, mandible QTLs have distinct and characteristic sites of action. Therefore, mandible morphology will be determined largely by the combination of these QTLs.