Exons 6 and 7 were flanked by loxP sites. In addition, an EGFP gene and Neo selection cassette separated by a loxP site and flanked by FRT sites was inserted upstream of the floxed exons 6-7. Flp-mediated recombination removed the FRT-flanked EGFP and Neo selection cassette, leaving an FRT site and floxed exons 6-7. (J:237188)