A one locus, biased mutation model and its equivalence to an unbiased model

Experimental data suggests that for some continuously varying characters under stabilising selection, mutation may cause a mean change in the value of the character. A one locus, mathematical model of a continuously varying biological character with this property of biased mutation is investigated. Via a mathematical transformation, the equilibrium equation describing a large population of individuals is reduced to the equilibrium equation describing a mutationally unbiased problem. Knowledge of an unbiased problem is thus su¢ cient to determine all equilibrium properties of the corresponding biased problem. In the biased mutation problem, the dependence of the mean equilibrium value of the character, as a function of the mutational bias, is non monotonic and remains small, for all levels of mutational bias. The analysis presented in this work sheds new light on Turelli's House of Cards approximation.