Exon 5 was flanked by loxP sites and an FRT site flanked reporter-selection double cassette was inserted into intron 4. The double cassette consists of a beta galactosidase (lacZ) gene cassette separated from a neomycin resistance gene cassette by a loxP site. The lacZ-neo double cassette was removed through flp-mediated recombination. (J:237769)