Transgenic construct used to study the mechanisms by which chromosomal position effects can effect expression of a w minigene. A loxP cassette containing a transcriptional terminator derived from the regulatory region of the Achaete-Scute gene complex has been inserted upstream of a w^+mC minigene, which carries an intact Wari insulator downstream of the w transcription unit. y regulatory and coding sequences are present upstream of the w^+mC minigene.