A model for the evolution of the genome: the effect of stochasticity on genetic loads.

In this paper a general model is given for the evolution of the genome incorporating stochastic factors. The model is applied to the substitutional genetic load problem. All of the major hard selection load formulae in the literature are extended and, where necessary, corrected (for stochasticity). Turning to rank selection, formulae for stochastic factors are also corrected and harmful mutations included. A simple formula for the selection coefficient as a function of the nonneutral substitution rate and the mutation profile is obtained. Further, it is noted that the formulae derived also apply (for different parameter values) to the mutation load, thus unifying the two loads under a single theory. A general formula for the mutation load under hard selection is given, extending previous results. Finally, the author derives a formula showing how many harmful mutations can be effectively eliminated by rank selection and discusses its relevance to the question of the possible buildup of harmful mutations in the human gene pool due to long-term exposure to low-level radiation.