The targeting vector is designed to insert a loxP site upstream of exon 3 and an FRT-flanked neomycin selection cassette, followed by a second loxP site, downstream of exon 5. Flp-mediated recombination removed the FRT-flanked neo cassette leaving exons 3 through 5 floxed. Cre-mediated recombination removed exons 3-5. (J:279981)