A loxP site was inserted upstream of exon 3 (originally identified as exon 1). An FRT-flanked neomycin resistance cassette with 5' loxP site was inserted downstream of exon 3 (originally identified as exon 1). Flp-mediated recombination removed the selection cassette and left exon 3 (originally identified as exon 1) floxed. (J:230288)