"Site-selected" transposon mutagenesis of Drosophila

Despite the wide range of techniques that can be brought to bear on the study of basic processes in Drosophila, there are still deficiencies in our armory. One of these is an ability to select mutants in cases where the gene is known and has been cloned, but where we are ignorant of the associated phenotype. We describe here a solution to this problem as applied to a model system, the singed (sn) locus. Our method is a combination of classical genetics and molecular biology: sib selection plus the polymerase chain reaction. We have used the method to isolate rare individuals with P-element-induced alleles of sn merely by recognition of the DNA structures induced at the locus by transposon insertion. Phenotypic criteria were used only retrospectively to verify our diagnoses. There are obvious implications of this technique for the mutagenesis of other organisms.