APC and polyposis: The dramatic polyposis in cecum and colon seen following bi-allelic Apc inactivation was significantly inhibited at both early and later time points by concurrent inactivation of one Ctnnb1 allele, with no grossly discernable epithelial phenotype seen in the proximal colon and only two to four polyps in the cecum per mouse as the CDX2P-G22Cre Apcfl/flCtnnb1fl/+ and CDX2P-CreERT2Apcfl/flCtnnb1fl/+ mice were aged (S1 Fig).