Genetic-molecular basis for a simple Drosophila melanogaster somatic system that detects environmental mutagens.

We have developed a simple, objectively scorable test for the mutagenicity of chemical compounds which can be fed Drosophila melanogaster. The test depends upon the somatic reversion of the X chromosome, recessive eye color mutation, white-ivory (wi) to wild type (w+). Reversions are scored as clones of w+ facets in the wi eyes of eclosing adults. To increase the sensitivity, a tandem quadruplication containing four wi mutations was synthesized. Thus, in homozygous females eight wi mutations are potentially revertible. Six mutagenic compounds, all alkylating agents, all gave positive results at several concentrations tested. Molecular analysis demonstrates that the induced reversions, germinal and somatic, are associated with the loss of 2.9-kilobase DNA duplicated in the wi mutation.