The Abcg5 and Abcg8 genes are in a head to head orientation. A loxP site and FRT-flanked neomycin cassette were introduced into intron 2 of the Abcg5 gene, and a loxP site was placed in intron 1 of the Abcg8 gene, generating a second allele, Abcg5tm1.1Hobb. Flpe-mediated recombination removed the FRT-flanked neomycin cassette.