Deletion-generation strategy based on the observation that when two P-element insertions are present at different sites on homologous chromosomes, upon exposure to P-transposase deletions that remove the region between the two insertions can be recovered. Resulting deletions are usually flanked by one of the starting P constructs, providing a molecular tag for subsequent breakpoint characterization; mechanism is thought to involve hybrid element insertion (HEI). Successfully used combinations of P{PZ}, P{lacW}, P{SUPor-P}, P{EP} and P{GT1} insertions. Recovered deletions whether the two P-element insertions were in the same or opposite orientations.

The resulting deletion breakpoints do not correspond exactly with the locations of the original insertions, but are usually very close. This appears to be due to a strong inherent bias of hybrid elements to insert in or near one of the original P insertions and was confirmed by the observation that there were only 2 deletions recovered in the HEI screens for which the breakpoints differed from the sites of the original P insertions at the level of polytene cytology.