The 5' P end of P{TV2-GMR} has been deleted and replaced with a duplicated fragment containing the promoter region and first two exons of the w^+mC marker. Thus, it consists of: 3' P end, a loxP site, GMR regulatory sequences, the GFP coding sequence (lacking a promoter), an FRT site, a w^+mC marker, GMR regulatory sequences, a loxP site, an Hsp70 core promoter, the GFP coding sequence, an FRT site and the duplicated portion of the w marker. In the absence of modification, GMR activity in cis can be assessed. Exposure to FLP creates a derivative (P{3'TV2-GMR.96C.-FRT}) that contains a "promoterless" GFP, while exposure to P1cre creates a derivative P{3'TV2-GMR.96C.-loxP} that contains an "enhancerless" GFP. These two derivatives can be combined to assess GMR activity in trans.