(A) Simulations of a spatially homogeneous zone of proliferation for three animals. Population mean number of stem cells per cross section, NSpop = 7, inter-animal standard deviation for number of stem cells per cross section, σpop = 1, intra-animal standard deviation for number of stem cells per cross section, σ = 0.5, probability of a cell to be proliferative (expected growth fraction), pp = 0.5, inter-animal standard deviation of pp, σp = 0.04, probability of a proliferative cell to be mitotic (expected mitotic index), pm = 0.015, inter-animal standard deviation of pm, σm = 0.003. (B) Simulations of two adjacent spatially homogeneous zones of proliferation for three animals. Parameters for the anterior zone are the same as in (A). The probability of a cell to be proliferative and probability of a proliferative cell to be mitotic in the posterior zone are elevated to pp = 0.8 and pm = 0.1, respectively. The mean switchpoint location is 300 μm anterior to the amputation plane and the corresponding inter-animal standard deviation is 100 μm. As expected, there are more proliferative and mitotic cells in the posterior zone. Simulation results can statistically be compared with the cell counts we obtained from experimentally observed animals to infer growth fraction, mitotic index and switchpoint (Figure 2F–F’’).