Molecular study of the germinal reversions induced at the white-ivory locus in Drosophila melanogaster.

The white-ivory somatic mutation test of Drosophila melanogaster is based on the reversion of the X-linked eye colour recessive mutation white-ivory to wild-type. Although the exact mechanism of white-ivory reversion is not quite understood, it has been suggested that such reversion, both in somatic and germ-line cells, could be due to the precise excision of the tandemly duplicated 2.96 kb DNA fragment characteristic of the white-ivory mutation. We have attempted to confirm this hypothesis analysing, at the molecular level, different germinal revertants induced by chemical treatment with three well known alkylating agents: ethyl methanesulphonate, methyl methanesulphonate and N-nitroso-N-ethylurea. The molecular analysis of these germ-line revertants, using Southern blot hybridization and polymerase chain reaction techniques, shows that such reversions are associated with the deletion of the 2.96 kb tandemly duplicated DNA sequence of the white-ivory locus.