Neutral mutation
Neutral mutations are changes in DNA sequence that are neither beneficial nor detrimental to the ability of an organism to survive and reproduce.
The most commonly-observed mutations that are detectable as variation in the genetic makeup of organisms and populations appear to have no visible effect on the fitness of individuals and are therefore neutral.
While Darwin is widely credited with introducing the idea of natural selection which was the focus of his studies, he also saw the possibility for changes that did not benefit or hurt an organism.
Kimura developed mathematical models of the behavior of neutral mutations subject to random genetic drift in biological populations.
While natural selection may encourage adaptation to a changing environment, neutral mutation may push divergence of species due to nearly random genetic drift.
This theory suggests that neutral mutations are responsible for a large portion of DNA sequence changes in a species.
[2] When an incorrect nucleotide is inserted during replication or transcription of a coding region, it can affect the eventual translation of the sequence into amino acids.
This phenomenon is referred to as degeneracy and allows for a variety of codon combinations leading to the same amino acid being produced.
Francis Crick proposed this theory to explain why specific tRNA molecules could recognize multiple codons.
The area of the tRNA that recognizes the codon called the anticodon is able to bind multiple interchangeable bases at its 5' end due to its spatial freedom.
If it occurs in an important structural area or in the active site, one amino acid substitution may inactivate or substantially change the functionality of the protein.
[18] The testable hypothesis of Kimura and others showed that polymorphism within species are approximately that which would be expected in a neutral evolutionary model.
This is a statistical test that compares polymorphism in neutral and functional sites and estimates what fraction of substitutions have been acted on by positive selection.
[33] Pauling and Zuckerkandl, proposed the idea of the molecular clock in 1962 based on the observation that the random mutation process occurs at an approximate constant rate.
By quantifying these neutral mutations in protein and/or DNA and comparing them between species or other groups of interest, rates of divergence can be determined.
While some paleontologists argue that molecular clocks are systemically inaccurate, others attribute the discrepancies to lack of robust fossil data and bias in sampling.
[37] While not without constancy and discrepancies with the fossil record, the data from molecular clocks have shown how evolution is dominated by the mechanisms of a neutral model and is less influenced by the action of natural selection.
