NATURALLY-OCCURRING VARIATION IN BRISTLE NUMBER AND DNA POLYMORPHISMSAT THE SCABROUS LOCUS OF DROSOPHILA-MELANOGASTER

The association between quantitative genetic variation in bristle numb er and molecular Variation at a candidate neurogenic locus, scabrous, was examined in Drosophila melanogaster. Approximately 32 percent of t he genetic Variation in abdominal bristle number (21 percent for stern opleural bristle number) among 47 second chromosomes from a natural po pulation was correlated with DNA sequence polymorphisms at this locus. Several polymorphic sites associated with large phenotypic effects oc curred at intermediate frequency. Quantitative genetic variation in na tural populations caused by alleles that have large effects at a few l oci and that segregate at intermediate frequencies conflicts with the classical infinitesimal model of the genetic basis of quantitative var iation.