Transgenic construct containing a y[+] marker upstream of a w gene which includes the eye enhancer. Two FRT sites have been inserted in opposite orientations: one is in the fourth intron of w and the other is downstream of the 3' end of the w transcription unit. The w sequence does not include the Wari insulator normally found downstream of the 3' end of the transcription unit. A loxP cassette containing a gypsy insulator has been inserted in the fourth intron of w, downstream of the first FRT site. A second gypsy insulator has been inserted downstream of the 3' end of the w transcription unit, upstream of the second FRT site and in the opposite orientation as the first gypsy insulator sequence.