The Glycosylation Sites in Influenza Virus PLOS ONE | www.plosone.org Current studies have analyzed the evolutionary dynamics of Nglycosylation sites of select subtypes or HA/NA as a whole [35] [36] [37] . Although most influenza evolution can be accounted for by genetic drift, there is also evidence of adaptive evolution of mutations which are under positive selection [38, 39] . We have extended previous studies of basic similarity alignment scoring of similarity to analyze the position-specific glycosites that are under selective pressure in IVs [40] . Here we present a detailed investigation of the distribution and the evolutionary pattern of the glycosites in the envelope glycoproteins of IVs, especially in the H5N1 virus.