THE NATURE OF QUANTITATIVE GENETIC-VARIATION REVISITED - LESSONS FROMDROSOPHILA BRISTLES

Most characters that distinguish one individual from another, like hei ght or weight, vary continuously in populations. Continuous variation of these 'quantitative' traits is due to the simultaneous segregation of multiple quantitative trait loci (QTLs) as well as environmental in fluences. A major challenge in human medicine, animal and plant breedi ng and evolutionary genetics is to identify QTLs and determine their g enetic properties. Studies of the classic quantitative traits, abdomin al and sternopleural bristle numbers of Drosophila, have shown that: ( 1) many loci have small effects on bristle number, but a few have larg e effects and cause most of the genetic variation; (2) 'candidate' loc i involved in bristle development often have large quantitative effect s on bristle number; and (3) alleles at QTLs affecting bristle number have variable degrees of dominance, interact with each other, and affe ct other quantitative traits, including fitness. Lessons learned from this model system will be applicable to studies of the genetic basis o f quantitative variation in other species.