ApcCKO/+ mice were intercrossed to generate ApcCKO/CKO offspring. Approximately one-quarter of the offspring (17 of 81) were homozygous for the ApcCKO allele. These mice as well as heterozygous mice for ApcCKO allele are normal, showing no differences in their survival to the wild-type littermates (Figure 1C). We tested whether our ApcCKO allele can compliment the wild-type allele by crossing the ApcCKO/CKO female with ApcΔ580/+ male mouse. The resultant ApcCKO/Δ580 offspring were viable and born in the Mendelian ratio, suggesting that the presence of loxP sites in introns flanking exon 14 have no adverse effect on the function of the Apc gene.