The efficiency of PCR amplification is either specified by an universal success rate , or, by a normal distribution  parameterized to capture GC preferential biases (default mean_GC=0.5 and SD_GC=0.1). Given p, the number of copies produced from a certain fragment is determined by random sampling under the cumulative binomial:

\[P_S(N)= \sum_{0}^{\lceil \frac{N}{2} \rceil}P_{S-1}(N-k) {N-k \choose k}  p^k (1-p)^{n-2k} \]