Quantitative Trait Loci for Early- and Late-Developing Skull Characters in Mice: A Test of the Genetic Independence Model of Morphological Integration.

Quantitative genetical theory suggests that characters existing in developmentally or functionally integrated groups are expected to be genetically correlated because they share a common inheritance. The genetic independence model for the cause of this genetic integration predicts that pleiotropic effects of single genes are mostly restricted to the characters in these integrated groups. We tested this model by estimating the additive and dominance effects of quantitative trait loci (QTLs) affecting early- (cranial vault) and late-developing (face) skeletal characters in F2 house mice originally derived from a cross of the Large and Small inbred strains. Interval mapping procedures were used that resulted in the identification of 26 QTLs on 17 of the 19 autosomes that significantly affected these characters. Additive, but not dominance, genotypic effects of many of these QTLs predominantly affected either the cranial vault or face characters, which supports the genetic independence model. Only two QTLs had positive pleiotropic effects on one group of characters but negative pleiotropic effects on the other (antagonistic pleiotropy).