PCR-based verification of murine splenocyte genotypes. Samples in lanes 2, 3, and 4 used the p53 exon 5 (W5′) and exon 7 (W3′) primers to assay for the presence of wild-type p53 PCR product. Samples in lanes 5, 6, and 7 used neo primers (M5′) and the p53 exon 7 reverse primers (W3′) to assay for a hybrid neo/p53 product expected in the p53 null mice. Murine wild-type DNA was used as PCR template in lanes 2 and 5, murine p53 null DNA was used in lanes 3 and 6, and no DNA templates were used in lanes 4 and 7 (negative controls). The expected p53 product from wild-type DNA is present in lane 2, and the expected neo/p53 hybrid product from p53 null DNA is present in lane 6. Lanes 1 and 8 are 100-bp ladders.