Transgenic construct that comprises an FRT cassette containing the w eye enhancer, a 3kb fragment of phage λ DNA, a mini-w gene and a gypsy\su(Hw)BR insulator. The regulatory 'R' region (nucleotides -33 to -111 relative to the w promoter) have been replaced with a fragment containing 4 copies of the sequence GCCGTCTCTTTCGCCGCTG.