CANDIDATE QUANTITATIVE TRAIT LOCI AND NATURALLY-OCCURRING PHENOTYPIC VARIATION FOR BRISTLE NUMBER IN DROSOPHILA-MELANOGASTER - THE DELTA-HAIRLESS GENE REGION

Delta (Dl) and Hairless (H) are two chromosome 3 candidate neurogenic loci that might contribute to naturally occurring quantitative variati on for sensory bristle number. To evaluate this hypothesis, we assesse d quantitative genetic variation in abdominal and sternopleural bristl e numbers among homozygous isogenic third chromosomes sampled from nat ure and substituted into the Samarkand (Sam) inbred chromosome 1 and 2 background; among homozygous lines in which the wild-derived Dl-H gen e region was introgressed into the Sam chromosome 3 background; and am ong Dl-H region introgression lines as heterozygotes against the Sam w ild-type strain and derivatives of Sam into which mutant Dl and H alle les had been introgressed. Variation among the Dl-H region introgressi on lines accounted for 36% (8.3%) of the total chromosome 3 among line variance in abdominal (sternopleural) bristle number and for 53% of t he chromosome 3 sex X line variance in abdominal bristle number. Natur ally occurring alleles in the Dl-H region failed to complement a Dl mu tant allele for female abdominal bristle number and sternopleural bris tle number in both sexes, and an H mutant allele for both bristle trai ts in males and females. These results are consistent with the hypothe sis that naturally occurring alleles at Dl and H contribute to quantit ative genetic variation in sensory bristle number.