The P{RS5r} transgene is generated in vivo by FLP-mediated excision of the FRT cassette in P{RS5}; this produces a "remnant" element that contains non-functional 5' portion of w upstream of a single FRT site.
An insertion of P{RS5r} can be used in conjunction with an insertion of P{RS3r} to induce a chromosomal rearrangement whose breakpoints are defined by the location of the original insertions.
FLPase-induced recombination between the FRT sites of P{RS5} leaves the 5' exon of w+mW.FRT.hs flanked on its 3' end by a FRT site oriented convergently with respect to the direction of w transcription.
