DECELERATION OF AGE-SPECIFIC MORTALITY-RATES IN CHROMOSOMAL HOMOZYGOTES AND HETEROZYGOTES OF DROSOPHILA-MELANOGASTER

Age-specific mortality trajectories were estimated in mixed-sex cohort s of D. melanogaster. We studied 22,000 flies that were either second- chromosome homozygotes or heterozygotes with a randomized genetic back ground. Broad-sense heritabilities for longevity were estimated to be 6% for males and 9% for females. Heterozygotes lived longer than homoz ygotes on average, but there were exceptions to the usual heterotic pa ttern; in several crosses parental homozygotes had average life spans as long as that of their F-1, heterozygotes. Estimated age-specific mo rtality rates were found to decelerate at advanced ages in both homozy gotes and heterozygotes. The mortality models that best fit the data a re the logistic model and the two-stage Gompertz model, both of which produce mortality trajectories that level off at advanced ages. Old-ag e mortality deceleration is not peculiar to inbred Drosophila.