Transgenic construct used to study the Mcp boundary element from the regulatory region of the Abd-B gene. Consists of the y body and wing enhancers, a FRT cassette containing the w eye enhancer, a fragment of the Mcp boundary element of Abd-B containing the Mcp silencer and a 210bp fragment of the Mcp insulator, the y gene, a loxP cassette containing a 755bp fragment of the Mcp boundary element (containing both the Mcp insulator and silencer) and a mini-w gene.