NOTE 18H: There is a subtlety here, when effective population size *N*_{e} differs from actual size *N*. The actual number of mutations generated at n loci is 2*nN*μ, but the probability that each one is fixed is 2*s*(*N*_{e}/*N*). Hence, the number of mutations that fix is 4*snN*_{e}μ. Thus, we can use the effective poulation size throughout the calculation: The actual number cancels.