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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}

Further, these patterns of clustering are reliably replicated using different data sets and marker types and show that the geographic origin of an individual is a reasonably good predictor of cluster assignment, although clusters lack discrete boundaries insofar . . . [Full Text of this Article]

Mike Bamshad, MD
mike@genetics.utah.edu
Department of Pediatrics
Eccles Institute of Human Genetics
University of Utah
Salt Lake City

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