Transgenic construct used in a systematic quantitative comparison of Polycomb/Trithorax response elements (PREs) and sequence variants at identical genomic locations. Generated in vivo by integration of donor plasmid sequence into the attP site present in the P{w3'.y+.attP} element. As a result of the integration event, a 1.6kb vg PRE fragment, with a deletion of the GAGA motif found in the first 106bp, is inserted directly upstream of a reconstituted w[+] reporter.