P-element mutagenesis.

Mobile elements were first used as a mutagenesis tool that introduces a molecular tag in the genes of interest. This facilitated subsequent molecular cloning and eventually promoted molecular analysis of a large number of fly genes. Soon after, P-elements were modified to detect genes not only based on a mutant phenotype but rather through revealing RNA or protein expression patterns (enhancer trap, gene trap). Owing to the typically imprecise mobilization of the P-elements these enhancer trap or gene trap insertions also provided means to generate (excision) mutants. Whereas the excision mutants are valuable deletions they are induced in a random fashion and the exact breakpoints have to be determined following molecular analysis. More recently, the introduction of recombination targets (flipase recombination targets) into P-elements has provided the ability to generate precise chromosomal deletions between preselected sites. Here we will summarize the current genetic approaches to generate different type of insertional and deletion mutations using specifically designed P-elements.