To simulate the introduction of new mutations, we simply add a random integer to the new child. Thus to create a new child named x from the ith member of the current generation, the code is:
x = g[i] + poisson(u);where poisson() is a function that implements a Poisson random number generator and u is the expected number of mutations.
Note that the variable u corresponds to the parameter of the mathematical model. For small values of the expected value the Poisson procedure described in Numerical Recipes  works fine. The average number of mutations per individual measured empirically over a wide variety of species is about 1.0, and the procedure in Numerical Recipes works for , so it should be sufficient.