Exons 14-16 were flanked by loxP sites. In addition, an EGFP and neomycin selection cassette separated by a loxP site and flanked by FRT sites was inserted upstream of the floxed exons 14-16. Flp-mediated recombination removed the FRT-flanked EGFP and neomycin selection cassette, leaving an FRT site and floxed exons 14-16. (J:276323)