Patterns of genetic variation in Mendelian and complex traits

This review discusses the prospects for understanding the genetic basis of complex traits in humans. We take the view that work done on Drosophila mel anogaster can serve as a model for understanding complex traits in humans, and the literature on this model system, as well as on humans, is reviewed. The prospects for success in understanding the genetic basis of complex tr aits depend, in part, on the nature of the forces acting on genetic variati on. We suggest that different experimental approaches should be undertaken for traits caused by common genetic variants versus those arising from rare genetic variants.