As expected a higher dN/dS ratio was observed for the surface glycoproteins, although none were directly influenced by positive selection. We observed that the HA1 region and the M2 protein have a slightly higher global dN/dS ratio than the other genes (Table 3 ). This is consistent with the findings of others [11, 61] . The M2 protein is a membrane ion channel protein on the surface of the virus molecule, a higher dN/dS ratio for this protein compared to the internal proteins is expected. The ratio might, however, be biased because the M2 protein is spliced from M and the dS is suppressed for overlapping regions giving a higher dN/dS ratio [11] .