Efficient and dispersed local P element transposition from Drosophila females

We have investigated how Drosophila P element insertions are distributed in the chromosomal region near their starting site. A single P element residing in the euchromatin of minichromosome Dp1187 was mobilized following a cross to the delta 2-3 (99B) strain, and progeny bearing transpositions were identified with a minimum of bias by performing Southern blots on progeny. Approximately 1-2% of all progeny minichromosomes contained new insertions. Many of these "local transpositions" landed very close to or within the starting P element; however, nearly 1% of all progeny chromosomes contained new insertions 1-180 kb from the donor element. More local insertions were observed in the progeny of females than from male parents, and most occurred in a preferred orientation relative to the starting element. These observations suggested that donor elements are frequently excised and reinserted locally without ever dissociating from a transposition complex. The high frequency and diverse distribution of local transpositions recovered from females suggested that the efficiency of insertional mutagenesis can be significantly enhanced by using a starting P element(s) located near the target of interest.