GENETIC INTERACTIONS BETWEEN NATURALLY-OCCURRING ALLELES AT QUANTITATIVE TRAIT LOCI AND MUTANT ALLELES AT CANDIDATE LOCI AFFECTING BRISTLE NUMBER IN DROSOPHILA-MELANOGASTER

Previously, we mapped quantitative trait loci (QTL) affecting response to short-term selection for abdominal bristle number to seven suggest ive regions that contain loci involved in bristle development and/or t hat have adult bristle number mutant phenotypes, and are thus candidat es for bristle number QTL in natural populations. To test the hypothes is that the factors contributing to selection response genetically int eract with these candidate loci, high and low chromosomes from selecti on lines were crossed to chromosomes containing wild-type or mutant al leles at the candidate loci, and the numbers of bristles were recorded in trans heterozygotes. Quantitative failure to complement, detected as a significant selection linecross effect by analysis of variance, can be interpreted as evidence for allelism or epistasis between the f actors on selected chromosomes and the candidate loci. Mutations at so me candidate loci (bb, emc, h, D1, Hairless) showed strong interaction s with selected chromosomes, whereas others interacted weakly (ASC, ab d, Scr) or not at all (N, mab, E(spl)). These results support the hypo thesis that some candidate loci, initially identified through mutation s of large effect on bristle number, either harbor or are close member s in the same genetic pathway as variants that contribute to standing variation in bristle number.