Quantitative inheritance and divergence inDrosophila populations.

Divergent sub-populations were obtained following relaxation of artificial selection for short wing in a population ofDrosophila melanogaster. Different results were obtained by relaxing the selection pressure in lines resulting from different selection procedures. The divergence was actually observed between lines derived by reciprocal crosses between vestigial and wild-type heterozygotes belonging to the same selection line. There was a difference in phenotypic variability in the two sub-lines from the start, which might be responsible for the differential response to natural selection. No difference in reproductive fitness has been detected between the divergent lines. The results can not be easily understood in the framework of an additive polygenic model; it is suggested that some complex interaction may be involved, acting on the developmental processes. It seems, however, safe to suggest that the divergence observed is determined by factors which are present in the FM line.