Exon 3 was flanked by loxP sites. The flanked fragment includes a sequence upstream of exon 3 (502 bp), 875 bp of the exon 3, and 497 bp of sequence downstream of exon 3. An FRT-flanked neomycin resistance cassette was inserted downstream of exon 3 before the second loxP site. Cre-mediated recombination removed exon 3 and the neomycin selection cassette. (J:296933)