Transposons of Drosophila (P elements)

P element of Drosophila consists mainly of 31 bp (base pairs) terminal inverted repeats enclosing a 3 kilobase protein coding region, coding for transposase and a repressor of transposition. Many P elements carrying internal deletions are also found, where the transposase derived from other complete P elements help their mobilization.

In these deleted P elements, foreign gene can be inserted to give recombinant P element, which can be microinjected into the fertilized egg, along with normal P element (helper P to supply transposase). The inserted gene is transposed onto an embryonic chromosome.