A loxP site was inserted upstream of exon 1. An FRT-flanked neomycin resistance cassette with a 3'loxP site was inserted downstream of exon 2. Flp-mediated recombination removed the neomycin resistance cassette and left exons 1 and 2 floxed. Cre-mediated recombination removed exons 1 and 2. (J:197556)