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Letters
January 25, 2006

Race and Genetic Influences on Health—Reply

JAMA. 2006;295(4):384-386. doi:10.1001/jama.295.4.385

In Reply: Drs Frank and Frank purport that “any categorization schema . . . to . . . partition [genetic] variation will . . . create artificial” boundaries because “the bulk of human genetic variation is continuously distributed.” This is a misconception. The bulk of human genetic variation consists of rare, population-specific polymorphisms that by definition cannot be continuously distributed.1,2 Common polymorphisms are more uniformly distributed among populations from neighboring geographic regions (ie, are distributed along clines). However, major geographic barriers precluded random mating throughout much of human history, generating small differences in polymorphism frequencies among the populations separated by these barriers.1 The cumulative information contained in these frequency differences can be used to distinguish genetic clusters concordant with populations separated by these barriers.1,3

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