Transgenic construct containing the y gene including wing and body enhancers upstream of the promoter. A loxP cassette containing five binding sites for the z protein (derived from the w gene) has been inserted at position -893 relative to the y transcription start site. An FRT cassette containing five binding sites for the z protein (derived from the w gene) has been inserted downstream of the y gene. This cassette is followed by a w minigene.