PLEIOTROPIC EFFECTS OF INDIVIDUAL GENE LOCI ON MANDIBULAR MORPHOLOGY

The genotypic basis of morphological variation is largely unknown. In this study we examine patterns of pleiotropic effects on mandibular mo rphology at individual gene loci to determine whether the pleiotropic effects of individual genes are restricted to functionally and develop mentally related traits. Mandibular measurements were obtained from 48 0 mice from the F-2 generation of an intercross between the LG/J and S M/J mouse strains. DNA was also extracted from these animals, and 76 m icrosatellite loci covering the autosomes were scored. Interval mappin g was used to detect chromosomal locations with significant effects on various mandibular measurements. Sets of traits mapping to a common c hromosomal region were considered as being affected by a single quanti tative trait locus (QTL) for mandibular morphology. Thirty-seven such chromosomal, regions were identified spread throughout the autosomes. Gene effects were small to moderate with the allele derived from the L G/J strain typically leading to larger size. When dominance was presen t, the LG/J allele was typically dominant to the SM/J allele. Most loc i affected restricted functional and developmental regions of the mand ible. Of the 26 chromosomal reg ions affecting more than two traits, 5 0% affect the muscular processes of the ascending ramus, 27% affect th e alveolar processes carrying the teeth, and 23% affect the whole mand ible. Four additional locations affecting two traits had effects signi ficantly associated with alveolar regions. Pleiotropic effects are typ ically restricted to morphologically integrated complexes.