Which DNA is moved is determined by sequences at the ends of the targets. Target specificity is determined by the transposase synthesized from a gene in the element. Fly embryos are microinjected with intact P elements and YFG flanked by target ends. Resulting flies have a single copy of YFG integrated into the chromosome. P element transformation is used to test whether isolated genes will complement known mutations.
Homologous recombination is used to insert payloads into larger vectors.