The number of mutations per cell division. The mutation rate can be determined from a Luria-Dulbruck fluctuation analysis. Sometimes the mutant frequency is described instead of mutation rate. The mutant frequency is simply the ratio of mutants / total cells in the population. The mutant frequency is much easier to measure but may show large fluctuations depending upon when the first mutation appeared in the population.

The rate at which changes occur in DNA sequence.Regions coding for proteins have a lower mutation rate than non-coding DNA since they may alter protein structure and are thus selected against.As an example, say the mutation rate of the coding region of mtDNA is approximately 1.7% per million years.Thus if a population of mtDNAs has an average difference of 0.3% within the coding region, one can estimate that they began to diverge from a common ancestor around 175,000 years ago (i.e., 0.3/1.7 million years ago).Because the mutation rate of the D-loop region in mtDNA is faster than the rate for the coding region, it will take less time to reach the same level of population diversity for this region.Because of this high mutation rate, reliance on the hypervariable D-loop region to establish phylogenetic networks is limited by the effects of saturation and homoplasy.

the number of new mutations that occur per gene per gamete per generation.

The speed at which mutations in an organism or a species take place.