Transgenic construct used to study interactions between insulator sequences. Consists of an FRT cassette containing the w eye enhancer, followed by followed by an 825bp DNA fragment containing the white-abutting resident insulator (Wari) in the forward orientation, the y transcription unit, a loxP cassette containing Wari in the reverse orientation and mini-w gene. The endogenous Wari insulator at the 3' end of the w gene is intact.