A loxP site was inserted upstream of exon 2 and a loxP and FRT flanked neo cassette was inserted downstream of exon 3 via homologous recombination. FLP-meditated recombination removed the neo cassette leaving exons 3 and 4 floxed, and Cre-mediated recombination in the germline resulted in the deletion of exon 2. (J:283074)