Transgenic construct used to study insulator function. Derived from P{dYW}; an FRT cassette containing eight reiterated su(Hw) protein binding sites derived from the gypsy insulator has been inserted at position -525 relative to the start of the y transcription start site (in between the body enhancer and the promoter). A loxP cassette containing a gypsy insulator fragment has been inserted downstream of the y coding region.