Transgenic construct used to study insulator function. Contains divergently transcribed w^+mC and y^+t7.7 marker genes. The y sequence includes the wing and body enhancers upstream of the promoter, and the bristle enhancer in intron 1. An FRT cassette containing a Fab-8 insulator fragment and GMR regulatory sequences (5 copies of the gl binding site) have been inserted in between the y body enhancer and y promoter, at a position corresponding to 200bp proximal to the site of the gypsy element insertion found in the y² allele.