FIG 3.

Clade characterization of H1N1 strains. (A) Clades determined by microarray hybridization for the gene segments of an A/H1N1pdm09 virus and a seasonal A/H1N1 virus. Gene segments that belong to different clades in the two strains are in bold. (B) Phylogenetic tree of the subtype 1 hemagglutinin gene showing the identified clades. The tree was inferred by maximum likelihood under the HKY + G substitution model. Classification of the H1 gene of the A/H1N1pdm09 virus within clade 1 indicates a swine origin, while the H1 from the A/H1N1 seasonal strain points to a human origin (clade 0).