page_title: Population genetics
section_title: Mutation
hierarchical_section_title: Population genetics / Four processes / Mutation
caption_attribution_description: English: This image shows a 0.1 x 0.03 inch (2.5 x 0.8 mm) small male Drosophila melanogaster fly. Français&#160;: Photographie de la drosophile "mouche du vinaigre" Drosophila melanogaster (dimensions réelles&#160;: 0.1 x 0.03 pouces (2.5 x 0.8 mm). Deutsch: Dieses Bild zeigt eine nur 2,5 x 0,8 mm kleine Schwarzbäuchige Taufliege (Drosophila melanogaster). Danke an Der Meister für Hilfe bei der Bestimmung. Polski: To zdjęcie pokazuje muszkę owocówkę (Drosophila melanogaster) o rozmiarach 2.5 x 0.8 mm. Italiano: Foto di una Drosophila melanogaster (moscerino della frutta) di dimensioni 2,5 x 0,8 mm. Türkçe: Bu görsel bir erkek meyve sineğini sergiler. Drosophila melanogaster. 2,5 x 0,8 mm büyüklüğünde. Camera data Camera Nikon D70 Lens Tamron SP AF 90mm/2.8 Di Macro 1:1 Focal length 90 mm Aperture f/32 Exposure time 1/60 s Sensivity ISO 200
context_page_description: Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.
  Population genetics was a vital ingredient in the emergence of the modern evolutionary synthesis. Its primary founders were Sewall Wright, J. B. S. Haldane and Ronald Fisher, who also laid the foundations for the related discipline of quantitative genetics. Traditionally a highly mathematical discipline, modern population genetics encompasses theoretical, lab, and field work. Population genetic models are used both for statistical inference from DNA sequence data and for proof/disproof of concept.
  What sets population genetics apart today from newer, more phenotypic approaches to modelling evolution, such as evolutionary game theory and adaptive dynamics, is its emphasis on genetic phenomena as dominance, epistasis, the degree to which genetic recombination breaks up linkage disequilibrium, and the random phenomena of mutation and genetic drift. This makes it appropriate for comparison to population genomics data.
context_section_description: Mutation is the ultimate source of genetic variation in the form of new alleles. In addition, mutation may influence the direction of evolution when there is mutation bias, i.e. different probabilities for different mutations to occur. For example, recurrent mutation that tends to be in the opposite direction to selection can lead to mutation–selection balance. At the molecular level, if mutation from G to A happens more often than mutation from A to G, then genotypes with A will tend to evolve. Different insertion vs. deletion mutation biases in different taxa can lead to the evolution of different genome sizes. Developmental or mutational biases have also been observed in morphological evolution. For example, according to the phenotype-first theory of evolution, mutations can eventually cause the genetic assimilation of traits that were previously induced by the environment.
  Mutation bias effects are superimposed on other processes. If selection would favor either one out of two mutations, but there is no extra advantage to having both, then the mutation that occurs the most frequently is the one that is most likely to become fixed in a population.
  Mutation can have no effect, alter the product of a gene, or prevent the gene from functioning. Studies in the fly Drosophila melanogaster suggest that if a mutation changes a protein produced by a gene, this will probably be harmful, with about 70 percent of these mutations having damaging effects, and the remainder being either neutral or weakly beneficial. Most loss of function mutations are selected against. But when selection is weak, mutation bias towards loss of function can affect evolution. For example, pigments are no longer useful when animals live in the darkness of caves, and tend to be lost. This kind of loss of function can occur because of mutation bias, and/or because the function had a cost, and once the benefit of the function disappeared, natural selection leads to the loss. Loss of sporulation ability in a bacterium during laboratory evolution appears to have been caused by mutation bias, rather than natural selection against the cost of maintaining sporulation ability. When there is no selection for loss of function, the speed at which loss evolves depends more on the mutation rate than it does on the effective population size, indicating that it is driven more by mutation bias than by genetic drift.
  Mutations can involve large sections of DNA becoming duplicated, usually through genetic recombination. This leads to copy-number variation within a population. Duplications are a major source of raw material for evolving new genes. Other types of mutation occasionally create new genes from previously noncoding DNA.
caption: Drosophila melanogaster
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