POLYGENIC MUTATION IN DROSOPHILA-MELANOGASTER - GENETIC INTERACTIONS BETWEEN SELECTION LINES AND CANDIDATE QUANTITATIVE TRAIT LOCI

We have investigated genetic interactions between spontaneous mutation s affecting abdominal and sternopleural bristle number that have accum ulated in 12 long-term selection lines derived from an inbred strain, and mutations at 14 candidate bristle number quantitative trait loci. The quantitative test for complementation was to cross the selection l ines to an inbred wild-type strain (the control cross) and to a deriva tive of the control strain into which the mutant allele at the candida te locus to be tested was substituted (the tester strain). Genetic int eractions between spontaneous mutations affecting bristle number and t he candidate locus mutations were common, and in several cases the int eraction effects were different in males and females. Analyses of vari ance of the (tester - control) differences among and within groups of replicate lines selected in the same direction for the same trait show ed significant group effects for several candidate loci. Genetically, the interactions could be caused by allelism of, and/or epistasis betw een, spontaneous mutations in the selection lines and the candidate lo cus mutations. It is possible that much of the response to selection w as from new mutations at candidate bristle number quantitative trait l oci, and that for some of these loci, mutation rates were high.