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Tajima's D is a population genetic test statistic created by and named after the Japanese researcher Fumio Tajima. [1] Tajima's D is computed as the difference between two measures of genetic diversity: the mean number of pairwise differences and the number of segregating sites, each scaled so that they are expected to be the same in a neutrally evolving population of constant size.
A mutation will increase genetic diversity in the short term, as a new gene is introduced to the gene pool. However, the persistence of this gene is dependent of drift and selection (see above). Most new mutations either have a neutral or negative effect on fitness, while some have a positive effect. [11]
This process is often characterized by a description of the starting and ending states, or the kind of change that has happened at the level of DNA (e.g,. a T-to-C mutation, a 1-bp deletion), of genes or proteins (e.g., a null mutation, a loss-of-function mutation), or at a higher phenotypic level (e.g., red-eye mutation).
Genetic variation is the difference in DNA among individuals [1] or the differences between populations among the same species. [2] The multiple sources of genetic variation include mutation and genetic recombination. [3] Mutations are the ultimate sources of genetic variation, but other mechanisms, such as genetic drift, contribute to it, as ...
The Nearly neutral theory stems from the prediction of neutral theory that the balance between selection and genetic drift depends on effective population size. [29] Nearly neutral mutations are those that carry selection coefficients less than the inverse of twice the effective population size. [30]
In 2015, the typical difference between an individual's genome and the reference genome was estimated at 20 million base pairs (or 0.6% of the total). [2] As of 2017, there were a total of 324 million known variants from sequenced human genomes. [3] Comparatively speaking, humans are a genetically homogeneous species.
The balance between the influence of natural selection and genetic drift on the population mutation rate is mainly determined by the population size. [5] Large populations are predicted to generally have lower mutation rates than smaller populations.
The "drifty gene hypothesis" [1] was proposed by the British biologist John Speakman as an alternative to the thrifty gene hypothesis originally proposed by James V Neel in 1962. [2] Speakman's critique of the thrifty gene hypothesis is based on an analysis of the pattern and level of mortality during famines. Despite much anecdotal evidence ...