Transgenic construct used in an enhancer-blocking assay to analyze boundary domain elements from the bithorax complex. Derived from P{wRW+we}; an approximately 2.8kb AflII fragment from the regulatory region downstream of the Abd-B gene (encompassing the hypersensitive sites HS1 and HS2) has been inserted between the w enhancer and w transcription unit. The AflII fragment contains Fab-8 (boundary) and iab-8PRE (silencer) sequences.