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Amplifying and Quantifying HIV-1 RNA in HIV Infected Individuals with Viral Loads Below the Limit of Detection by Standard Clinical Assays
Published on: September 26, 2011
Human immunodeficiency virus type 1 molecular evolution and the measure of selection
1Department of Microbiology, University of Washington, Seattle 98195-7740, USA.
Abstract:
Human immunodeficiency virus (HIV) envelope genes are highly variable between and often within individuals. Part of this variability is thought to be the result of immune-mediated positive selection for sequence diversity. To measure positive selection it has become customary in HIV research to calculate the ratio of the proportions of synonymous (ds) and nonsynonymous (dn) substitutions per potential synonymous or nonsynonymous site, respectively. However, another measure that can be used is the difference between ds and dn, delta d. We show, by example, that using the ratio, ds/dn, or the difference, delta d, may lead us to different conclusions regarding the existence of positive selection pressure. We conclude by noting that until we understand the processes that mediate nucleotide variation in a host selective environment, inferences based on summary statistics characterizing types of nucleotide substitutions should be made with caution.
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