Final answer:
Influenza evolves via antigenic drift, which involves minor point mutations, and antigenic shift, which involves major gene reassortment. The main proteins affected are the surface proteins hemagglutinin and neuraminidase. Antigenic shift has the potential to lead to pandemics due to the novel protein combinations that may not be recognized by the immune system.
Step-by-step explanation:
Influenza is caused by RNA influenza viruses that evolve through small changes taking place by antigenic drift, and through major changes taking place by the reassortment of the genetic material from different strains. Antigenic drift refers to the form of slight antigenic variation that occurs because of point mutations in the genes that encode surface proteins. In contrast, antigenic shift is a form of major antigenic variation that occurs because of gene reassortment, typically when two different influenza viruses infect the same host simultaneously.
The surface proteins primarily affected by these mutations and reassortments are the spike proteins hemagglutinin (H) and neuraminidase (N), both of which play crucial roles in the viral infectious cycle. Antigenic drift leads to slight changes over time, whereas the antigenic shift can result in the creation of a new virus with a mixture of proteins from the original viruses, often leading to pandemics as the immune system is less likely to recognize and fend off these new variants.