FIG. 1.

Breeding scheme to generate the hCYP1A1_CYP1A2_Cyp1a1/1a2(−/−)-Ahr^d (Ahr^d) mouse line. The hCYP1A1_CYP1A2_Cyp1a1/1a2(−/−)-Ahr^b1 mice were crossed with B6.D2-Ahr^d congenic mice to produce heterozygotes, following which homozygous humanized mice harboring two Ahr^d alleles on a >99.8% C57BL/6J genetic background were created. Homozygotes for the hCYP1A1_1A2 insertion can be generated one-fourth of the time by mating two heterozygotes, but we cannot distinguish heterozygotes from homozygotes by our current PCR genotyping, because the region of chromosomal insertion is unknown. The only way to distinguish between these two would be to measure the copy number of the hCYP1A1_1A2 genes. Consequently, the data from both hCYP1A1_1A2 lines represent a mixture of heterozygotes and homozygotes at the hCYP1A1_CYP1A2 locus.