Genetic heterogeneity among the founders of laboratory populations of Drosophila melanogaster : V. Sternopleural and abdominal chaetae in the same strains.

1. Single inseminated females of Drosophila melanogaster derived from the same population led to discrete strains for both Sternopleural and abdominal chaeta number in agreement with other work, which indicates that the wild populations have genes polymorphic for these traits. Variability varied significantly between strains for Sternopleural but not abdominal chaeta number. 2. Overall, the data show a weak correlation between the two traits. Considering this by strain, the correlations go from negative (but not significantly < 0) to positive (but significantly > 0). Therefore just as the rate of response to directional selection has been shown to be extremely rapid when based on strains extreme in the direction of the required selection response, it seems that a similar process may be useful for directional selection based on two traits simultaneously, by using only those strains showing a positive correlation.