Progressive resistance against the male recombination factor 31.1 MRF acquired by Drosophila melanogaster.

A genetically abnormal but structurally normal second chromosome (31.1 MRF) which induces recombination in the male sex, was introduced by outcrossing into the cytoplasm of a normal strain. In this new combination, male recombination frequency induced by females dropped from 3.81% to 0.17% within 10 generations, indicating a gradual acquisition of resistance against the activities of the 31.1 MRF.