Analysing the effect of genetic drift on the distribution of a mutation in rapidly growing populations.

The Wright-Fisher model is widely used in population genetics to study evolutionary processes. While the human population size has been growing exponentially since the advent of agriculture approximately 500 generations ago, population geneticists have focused this model more on constrained populations. Simulation of this model for exponentially growing populations and inference from these simulations is therefore of widespread interest. This study addresses the question of why inherited mutations like those that cause albinism have not gone extinct nor fixed. In particular, the study simulates the Wright-Fisher model for exponentially growing populations and compare the results to those from solutions of diffusion approximation equation. We show that instead of mutant alleles in a rapidly growing population necessarily converging to either extinction or fixation, mutations may coexist with the native alleles. Further, we show that the diffusion equation best approximates the Wright-Fisher model when growth rate of the population is low. This study concludes that genetic drift in rapidly growing populations is sufficient to account for the observed frequencies of alleles that cause albinism and its persistence in different populations in sub-Sahara Africa. Thus, it is not necessary to invoke other factors such as selection pressure, migrations and cultural patterns although these may also play a role.