Transgenic construct used to study the Mcp boundary element. Consists of a 755bp fragment of the Mcp boundary element of Abd-B (contains the silencer and the insulator), the y wing enhancer, an FRT cassette containing the w eye enhancer, the y body enhancer, the y gene (including the bristle enhancer), a loxP cassette containing the 755bp fragment of the Mcp boundary element and a mini-w gene.