Genetic analysis of extended life span in Drosophila melanogaster - II. Replication of the backcross test and molecular characterization of the N14 Locus

We are interested in localizing chromosomal regions that extend life span i n Drosophila. Using stocks artificially selected for long life by Luckinbil l and his colleagues, we have identified marker loci that are highly diverg ent in allelic frequencies between replicated long-lived lines and controls (Curtsinger et al., 1998). Several of the most divergent loci have been fo und to be associated with effects on life span in segregating backcross pop ulations. Here we report an independent replication of the backcross test f or the N14 marker locus, previously reported to extend male life spans by 1 2 days. The life span effect successfully replicates in males. N14 accounts for 30% of the total selection response in males. Life span extension occu rs by a decrease in age-specific mortality rates at all ages, and is not at tributable to modification of the slope of the age-specific mortality curve . The effect in females is small or nonexistent. Sequencing of the N14 locu s shows that it is non-coding and not obviously regulatory, suggesting that the phenotypic effect arises from linkage disequilibrium with another locu s or loci that directly affect life span. N14 DNA hybridizes to 63F/64A on the left arm of chromosome 3. The location is consistent with previous whol e-chromosome substitution studies, and suggests new candidate genes for lif e span extension in Drosophila, including ras2.