The Effects on Individual Loci on Mandibular Morphology 

Victor Ekuta and James Cheverud

Department of Anatomy and Neurobiology, Washington University School of Medicine

  

Individual differences in most phenotypic traits are affected by genes at many different loci and the environment. In this study we tested hypotheses about the influence of individual genetic loci on the variation found in mouse mandibular morphology. The mouse mandible has long served as a model for investigating complex phenotypes and consequently, much is known about its developmental and functional properties. Furthermore, mandibular traits tend to be moderately heritable. Mandibular measurements were obtained from the F₁₀ generation of an advanced intercross line (AIL) produced by intercrossing two inbred mouse strains, Small(SM/J) and Large (LG/J), followed by eight rounds of random mating. The effects of QTLs on mandibular measurements were determined by interval mapping where the contributions of individual parts of the genome to the individual differences in each trait were evaluated using a LPR score (log probability ratio score). Chromosomal locations with LPR scores greater than 10 were considered statistically significant and marked as likely QTLs. Many QTL were detected for most traits at various intervals spread throughout the autosomes. Pleiotropy – where one locus has effects on more than one phenotypic trait – was suggested by the fact that QTL discovered for different traits were sometimes at similar locations in the genome. The results of this study provide further evidence that individual differences in complex phenotypes are due to the action of genes at many loci and environmental effects. Currently, we are comparing these results with results obtained by studies of previous generations in this experiment to determine whether QTL found in the different generations are found in the same location and also identify the genes that reside in the QTL intervals.