To assess the molecular effects of the K14-cre–mediated recombination, we screened for the presence of deleted Apc (ApcΔ580) alleles. Genomic DNA was extracted from liver, thymus, and skin from all 4 possible genotypes: K14-cre; ApcCKO/CKO, K14-cre; ApcCKO/+, ApcCKO/CKO, and ApcCKO/+. Genotyping on genomic DNA from these tissues showed that the ApcΔ580 allele (500-bp product) was detected only from the skin and thymus of the K14-cre–positive mice. The presence of mutant Apc allele in the thymus of K14-cre; ApcCKO/+ mice was consistently much less than the DNA from the skin of the same animal or other tissues from the KA mutants. In addition, this product was not detected at all in either the liver of K14-cre–positive or in any of the K14-cre–negative mouse tissues samples, establishing that Cre-mediated recombination has taken place in the tissue-specific manner in the mice that inherited K14-cre (Figure 3A).