APC and breast cancer: Comparison of genomic DNA isolated from normal ApcMin/+ mammary tissue using a PCR-based assay followed by quantification of the ratio of Apc+ to ApcMin alleles demonstrated that mammary tumors from MMTV-PyMT;ApcMin/+ mice generally retain the wildtype allele (Figure S1), suggesting that haploinsufficiency for Apc promotes tumor development in the MMTV-PyMT model.