The targeting vector is designed to insert a loxP site upstream of exon 13 and an FRT-flanked neomycin resistance (neo) cassette, followed by a second loxP site, downstream of exon 22, which includes the STOP codon. Flp-mediated recombination removed the FRT-flanked neo cassette leaving exons 13 through 22 floxed. (J:101977)