Mutation rate

The upper and lower limits to which mutation rates can evolve is the subject of ongoing investigation.

[4] When the mutation rate in humans increases certain health risks can occur, for example, cancer and other hereditary diseases.

Having knowledge of mutation rates is vital to understanding the future of cancers and many hereditary diseases.

The distribution of fitness effects of new mutations is an important parameter in population genetics and has been the subject of extensive investigation.

[6] Although measurements of this distribution have been inconsistent in the past, it is now generally thought that the majority of mutations are mildly deleterious, that many have little effect on an organism's fitness, and that a few can be favorable.

As an example, mutation rates have been directly inferred from the whole genome sequences of experimentally evolved replicate lines of Escherichia coli B.

Mutation accumulation lines have been used to characterize mutation rates with the Bateman-Mukai Method and direct sequencing of well-studied experimental organisms ranging from intestinal bacteria (E. coli), roundworms (C. elegans), yeast (S. cerevisiae), fruit flies (D. melanogaster), and small ephemeral plants (A.

Mutation rates can also differ even between genotypes of the same species; for example, bacteria have been observed to evolve hypermutability as they adapt to new selective conditions.

That is not necessarily due to a higher mutation rate, but to lower levels of purifying selection.

For instance, Paramecium tetraurelia has a base-substitution mutation rate of ~2 × 10−11 per site per cell division.

The low mutation rate in Paramecium has been explained by its transcriptionally silent germ-line nucleus, consistent with the hypothesis that replication fidelity is higher at lower gene expression levels.

[20] The highest per base pair per generation mutation rates are found in viruses, which can have either RNA or DNA genomes.

From this full de novo spectrum, for instance, one may calculate the relative rate of mutation in coding vs non-coding regions.

[26] or, as reviewed by Bernstein et al.[27] having increased energy use for repair, coding for additional gene products and/or having slower replication).

[28][29] As such, hypermutation enables some cells to rapidly adapt to changing conditions in order to avoid the entire population from becoming extinct.