Evolutionary dynamics under the Moran process. (a) When normal cells divide, there is a probability μ that one of the daughter cells will have a mutation, while with probability 1 - μ no mutation occurs. Mutant cell replication increases the number of mutant cells - no back mutations are allowed. (b) Cells have a relative reproductive fitness r compared to normal cells, which have a fitness 1. (c) The probability that a cell is chosen for reproduction (P
for mutant and P
for normal cells) is dependent both on its frequency and its relative fitness. If j is the number of mutant cells at that time and N is the total number of cells present, the number of normal cells will be N - j. Since a cell has to be chosen at any time - if a mutant cell is not chosen for reproduction, a normal cell will be chosen.