Mutation rate refers to the frequency of new mutations per generation in an organism or a population. Mutation rates can be determined fairly precisely in experimental organisms with short generation times, such as bacteria or fruit flies. Human mutation rates are more difficult to determine accurately. Mutation rates can be used as a "molecular clock" to determine the time since two species diverged during their evolution.

Measurements of Mutation Rate

Mutation rate is often difficult to measure. The frequency of existing mutations in a population is not a good indication of the mutation rate, since a single mutation may be passed on to many offspring. In addition, there are often selective pressures that increase or decrease the frequency of a mutation in a population.

Mutation rates differ widely from one gene to another within an organism and between organisms. Generally mutation rates in bacteria are about...