A loxP site was inserted upstream of exon 13. An FRT-flanked neo cassette with a 3' loxP site and modified exon 13 with an insertion of an in-frame lacZ gene. Flp-mediated recombination removed the neo cassette and left exon 13 floxed. Gerline-mediated cre recombination removed the loxP flanked sequences including the endogenous exon 13, creating a null allele and reporter. (J:249016)