Transgenic construct used in a pairing-sensitive repression (PSR) assay. Contains a 2.9 kb XbaI-PstI fragment from upstream of ph-p (nucleotides 72,935 to 70,027 of AE003423), followed by the w+mC minigene, the lacZ coding region and a 2.3 kb XhoI-BamHI fragment from upstream of ph-d (nucleotides 60,771 to 58,448 of AE003423). The distance between the ph-p and ph-d sequences in this construct roughly mimics the separation and relative orientation of these two fragments in the genome.