Quantitative genetic differences between populations of Drosophila melanogaster from diverse geographic origins

Crosses were made between each seven populations of Drosophila melanogaster-three of which were laboratory populations and four were recently captured populations-and a line previously selected for low sternopleural bristle number for many generations. In each of six replicate lines from each cross, selection was practised for low sternopleural bristle number; subsequently these replicates were intercrossed and reselected. Introduction of new genetic material from four populations into the selected line was achieved, indicating the presence in these populations of particular alleles which are absent from or rare in the base populations of the selected line. Introduction of new genetic material from three populations into the selected line was not achieved. Consequently, it was possible to establish two groups of populations. In each group, the populations appear to be segregating for essentially the same alleles. Differences in gene frequency rather than the presence or absence of particular alleles are mainly responsible for the differences observed between the populations.In all, 11 populations screened for genetic differences controlling sternopleural bristle number. There are widespread genetic similarities among populations of very different geographic origin. Laboratory populations as a group are not more homogeneous than recently collected populations, although the latter are genetically more variable. Drift alone could account for the reduction of variability in the laboratory populations.