Transgenic construct used to study sequences required for Polycomb response element (PRE) silencing in vivo. Contains a w[+] minigene in which a 260bp subfragment of the iab-7PRE, with mutations in the PCC-binding element (PBE) (mutations are in the downstream flanking motifs of pho protein binding sites 4 and 5), has been inserted between the w enhancer and w transcription unit.