The mutation component of genetic damage.

The mutation component, M, is a measure of the proportion of the impact of a genetic condition that is attributable to recurrent mutation. For a trait maintained by balance between mutation and directional selection, M is approximately the broad-sense heritability; for a measured character where the mean and optimum coincide, M is about half the heritability. If the narrow-sense heritability is high, the impact changes relatively rapidly with a change in mutation rate. If the narrow-sense heritability is low, M cannot be predicted, but the change in impact following a change in mutation rate, if any, is very slow.