Transgenic construct containing direct FRT sites flanking a non-functional rearranged w gene (the 3' portion is fused upstream of the promoter plus 5' portion). The construct also carries a v^+t1.8 marker outside of the FRT sites. In the presence of FLP recombinase, the w sequence is excised onto an extrachromosomal episome and the normal 5'-3' organization is restored. The episomal w reporter contains a 670bp w eye enhancer upstream of the w promoter and coding sequence, with a 5.5kb intronless y gene (including wing and body enhancers) inserted in between the w enhancer and promoter sequence.