UAS regulatory sequences are followed by an FRT cassette that contains a coding sequence (CDS) encoding cid tagged at the C-terminal end with GFP. Following the FRT cassette is a second CDS that encodes cid tagged at the C-terminal end with mKO. In the absence of FLP recombinase, only the GFP-tagged cid CDS is expressed. Upon excision of the FRT cassette using FLP, the mKO-tagged cid CDS is expressed.