The genetic basis of load and inbreeding depression has important implications for the evolution of mating systems and management of rare and endangered species. Yet the best data available consider viability load at the level of whole chromosomes in Drosophila. The Principal Investigator proposes to measure the load attributable to small (ca. 10 centiMorgan) chromosome segments in the plant Brassica campestris. Maximum likelihood methods to map QTL onto short chromosomal regions marked by restriction fragment length polymorphism (RFLP) will be employed.By determining the degree to which small QTL bearing chromosome segments contribute to load by overdominance, dominance, or epistasis, the researchers can begin to infer the distribution of effects for loci contributing to genetic load and inbreeding depression. Most previous studies have examined single fitness components in one environment, precluding the possibility of overdominance induced by pleiotropy among fitness components or genotype x environment interaction. This research project will measure viability and fecundity in both field and greenhouse to give more accurate estimates of overdominance. This study represents the next step towards resolving the basis of genetic load at the gene level by combining molecular and quantitative genetics.
