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]

Measures of genetic distance

There are several measures used to indicate genetic distance.^[2] These include:

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.

Nei's standard genetic distance

This measure assumes that genetic differences arise due to mutations and genetic drift.^[3]

Cavalli-Sforza and Edwards 1967

This measure assumes that genetic differences arise due to genetic drift only.

Reynolds, Weir, and Cockerham's 1983

This measure assumes that genetic differences arise due to genetic drift only.

See also

• Human genetic variation
• Human genetic clustering

References

1. ^ Genes, Peoples, and Languages By L. L. (Luigi Luca) Cavalli-Sforza ISBN 0520228731 ]
2. ^ Population Genetics IV: Genetic distances -- biological vs. geometric approaches.
3. ^ Nei et al. (1973). SAMPLING VARIANCES OF HETEROZYGOSITY AND GENETIC DISTANCE. http://www.genetics.org/cgi/content/abstract/76/2/379. 

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