Genetics. Published Articles Ahead of Print: March 4, 2007, Copyright © 2007
doi:10.1534/genetics.106.067355


A more recent version of this article appeared on May 1, 2007.


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Genetic Similarities Within and Between Human Populations

1 University of Utah
2 University of Texas Southwestern Medical Center
3 Louisiana State University

* To whom correspondence should be addressed. E-mail: lbj{at}genetics.utah.edu.

Submitted on October 25, 2006
Revised on January 10, 2007
Accepted on 5 February 2007


Abstract

The proportion of human genetic variation due to differences between populations is modest, and individuals from different populations can be genetically more similar than individuals from the same population. Yet sufficient genetic data can permit accurate classification of individuals into populations. To resolve this apparent conflict, we analyzed the question "How often is a pair of random individuals from two different populations genetically more similar than a pair of individuals randomly selected from any single population"; We compared this frequency (w) with error rates for classification methods, using data sets that vary in number of loci, diversity of populations, and polymorphism ascertainment strategies. Classification methods achieve higher discriminatory power than the individual-based measure, w, because of their use of aggregate properties of populations. The number of loci analyzed is the most critical variable: with one hundred polymorphisms, accurate classification is possible, but w remains sizable, even when using populations as distinct as sub-Saharan Africans and Europeans. Phenotypes controlled by a dozen or fewer loci can be expected to show substantial overlap between human populations. This provides empirical justification for caution when using population labels in biomedical settings, with broad implications for personalized medicine, pharmacogenetics, and the meaning of race.

Key Words: classification, genetic polymorphism, human population, race, variation




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