A targeting vector was designed to insert loxP sites flanking exon 7. A FRT-flanked neomycin (neo) resistance cassette was inserted into intron 6 and a frt-flanked puromycin (puro) resistance cassette was inserted into intron 7. Flp-mediated recombination removed the FRT-flanked neo and puro cassettes leaving exon 7 floxed. (J:227671)