A conditional protein tag sequence has been inserted at the Dg locus near the stop codon. The inserted sequence comprises 1. an FRT cassette that contains a 1xTag:V5 tag followed by a stop codon and a single loxP site, 2. a 3xTag:FLAG tag followed by a stop codon. In the absence of FLP, the Dg protein is tagged with Tag:V5. If the FRT cassette is excised using FLP, the Dg protein is instead tagged with Tag:FLAG.