FIG 7.

Phylogenetic trees showing the emergence of pandemic mutations. The far left tree is colored and ordered temporally by Northern Hemisphere influenza season and used as a reference tree. The trees to the right of the reference tree are colored by the residues that are present at the site labeled above the specific tree. Strains carrying the amino acid that was dominant in the early 2009 pandemic outbreak sequences (group 1) are colored blue; strains carrying the amino acid that was dominant in the late pandemic sequences (group 2) are colored red. Strains carrying all other residues are colored gray.