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