MM mutant cells measured over 5 years in a patient with polycythemia rubra vera. Each point on the graph represents the mutant frequency at the sampled time point. The dotted line indicates uncertainty, as blood was not sampled during this period. The panels on the right show examples of flow cytometric output from which the graph is based. Fluorescence from the M and N blood groups is measured on the vertical and horizontal axes, respectively. The original MN heterozygote cells are detected in box I, while MM mutant cells are detected in box G.