Mi{FlpTag.1} is designed to allow conditional gene tagging. It contains an artificial exon composed of a splice acceptor site, EGFP and a splice donor site; this sequence can act as a protein trap element when inserted into a phase 1 coding intron of an endogenous gene in the correct orientation. The protein trap exon is flanked by two pairs of target sites for FLP-mediated recombination (FRT and FRT14), which form a flip-excision (FLEx) switch (design principles described in PMID:12665802), which means that the protein trap exon can be inverted using FLP recombinase and then stably locked in the opposite orientation, generating the Mi{FlpTag.1.lock} transgene. Mi{FlpTag.1} is generated in vivo by using a donor construct containing the FlpTag cassette flanked by attB sites to replace the RMCE cassette present in an insertion of a Mi{MIC} element in a coding intron of a gene of interest. For the FlpTag approach, a Mi{FlpTag.1} insertion in the opposite orientation to the direction of transcription of the gene of interest is typically initially chosen, so that in the absence of FLP the gene is not tagged. Then, upon expression of FLP recombinase, the protein trap exon is stably inverted so that it is in the same orientation as the gene of interest, resulting in it being tagged with EGFP.