Genetic distance
Genetic distance refers to the genetic divergence between species or between populations within a species. It is measured by a variety of parameters. Smaller genetic distances indicate a close genetic relationship whereas large genetic distances indicate a more distant genetic relationship. Genetic distance can be used to compare the genetic similarity between different species, such as humans and chimpanzees. Within a species genetic distance can be used to measure the divergence between different sub-species.
In its simplest form, the genetic distance between two populations is the difference in frequencies of a trait. For example the frequency of RH negative individuals is 50.4% among Basques, 41.2% in France and 41.1% in England. Thus the genetic difference between the Basques and French is 9.2% and the genetic difference between the French and the English is 0.1% for the RH negative trait. The genetic distance of several individual traits can then be averaged to compute an overall genetic distance.[1]
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[edit] Measures of genetic distance
There are several measures used to indicate genetic distance.[2] These include:
[edit] Fixation index
A commonly used measure of genetic distance is the fixation index which varies between 0 and 1. A value of 0 indicates that two populations are genetically identical whereas a value of 1 indicates that two populations are different species.
[edit] Nei's standard genetic distance
This measure assumes that genetic differences arise due to mutations and genetic drift.[3]
[edit] Cavalli-Sforza and Edwards 1967
This measure assumes that genetic differences arise due to genetic drift only.
[edit] Reynolds, Weir, and Cockerham's 1983
This measure assumes that genetic differences arise due to genetic drift only.
[edit] See also
[edit] References
- ^ Genes, Peoples, and Languages By L. L. (Luigi Luca) Cavalli-Sforza ISBN 0520228731 ]
- ^ Population Genetics IV: Genetic distances -- biological vs. geometric approaches.
- ^ Nei et al. (1973). SAMPLING VARIANCES OF HETEROZYGOSITY AND GENETIC DISTANCE. http://www.genetics.org/cgi/content/abstract/76/2/379.
[edit] External links
- A review of mutation processes and methods of phylogenetic inference, David B. Goldstein, David D. Pollock
- Stanford University website on genetic distance
- The Estimation of Genetic Distance and Population Substructure from Microsatellite allele frequency data., Brent W. Murray (May 1996), McMaster University website on genetic distance
- Computing distance by stepwise genetic distance model, web pages of Bruce Walsh at the Department of Ecology and Evolutionary Biology at the University of Arizona
- Britten RJ. Divergence between samples of chimpanzee and human DNA sequences is 5%, counting indels. PNAS; 2002:13633
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