Competitive long-term reconstitution assay. Detection of the p53 knock-out and the wild-type allele in BMCs of TBI-treated mice injected 16 weeks earlier with a 1:1 mixture of p53+/+ and p53−/− BMCs by PCR followed by Southern blotting (left panel: 1, 2, 3, and 4 individual mice). Known mixtures of p53+/+ and p53−/− cells (percentages indicated on the top or bottom of the blot) were analyzed to generate a calibration blot (right panel).