Reproduction in Cage Populations of a Polymorphism Regularly Observed in the Natural Populations of DROSOPHILA MELANOGASTER in France.

Polymorphism for both alleles of a gene ref(2)P, which is a usual trait of French natural populations of Drosophila melanogaster , can be reproduced in experimental conditions. ref(2)P is a gene for resistance to the hereditary, noncontagious Rhabdovirus sigma, responsible for CO(2) sensitivity in Drosophila melanogaster . The equilibrium frequencies observed in cages are the same as in the wild, whether sigma virus is present or not. The rapid rate of return to these equilibrium frequencies indicates that strong forces, which remain to be determined, are responsible for the maintenance of this polymorphism.