Fig. 5. P element replacement. (A) Two P elements, an acceptor element, containing marker 1 (orange), and a donor element, containing transgenic insert (red) and marker 2 (yellow), are brought together. (B) In the presence of P transposase, the acceptor element might excise. (C) This excision might promote double-stranded gap repair through homologous recombination between the 10-20 bp footprints (pink) of the 31 bp inverted terminal repeats at the acceptor site (blue) and the similar sequence at the donor site (green). (D) This results in the integration of the donor element into the acceptor locus.