Geneticists use the term mutation rate to indicate the probability that a given nucleotide will be changed by a spontaneous mutation. Mutation rates are expressed as the chance of a mutation per round of replication, per gamete (in eukaryotes), or per cell division (in prokaryotes). Mutation rates also vary considerably between organisms. Bacteria and viruses tend to have higher mutation rates due to the fact that they do not generally possess efficient mechanisms of DNA repair. The mutation rate for humans is 1× 10−5 to 1 × 10 −6 . In other words, a single nucleotide has a chance of mutation once per million to 10 million gametes. Mutation rates are not precise measurements. Rather, they are considered to represent the probability of mutation. Geneticists recognize that mutation rates are not consistent throughout the genome. Areas of the genome that contain repetitive sequences are more prone to mutation than other areas. These are called mutational hot spots, and they have been discovered in the genomes of most organisms. Geneticists who are concerned with mutations at the population level use the term mutation frequency to indicate the rate of a specific mutation within a population. This term does not indicate the chances that the mutation will arise spontaneously within the population, but rather the estimated percent of the population that carries the mutation.
