Transgenic construct used to study functional interactions between two insulators. Consists of the y wing enhancer, an FRT cassette containing the w eye enhancer, the y body enhancer, a 825bp Wari (white abutting resident insulator) fragment, the y gene, a loxP cassette containing a 430bp gypsy\su(Hw)BR insulator fragment, a mini-w gene with a deletion of a considerable part of the first intron and a 825bp Wari fragment.