Which statement best describes the subdivision of influenza viruses into subtypes and strains?

Which statement best describes the subdivision of influenza viruses into subtypes and strains?

• A. They are grouped by differences in surface proteins and host range.
• B. They are grouped by DNA content.
• C. They are grouped by color.
• D. They are grouped by replication speed.

Answer: (A)

Differences in the viral surface proteins and the host range determine how influenza is categorized. The main surface proteins, hemagglutinin and neuraminidase, come in multiple forms, and their specific combinations define subtypes (like H1N1 or H3N2). These surface proteins govern how the virus attaches to and enters cells and how the immune system recognizes the virus, which also influences which species can be infected. Because of this, grouping by these surface-protein differences and by host range best reflects how influenza is subdivided into subtypes and strains. Other ideas don’t fit: influenza is an RNA virus, so DNA content isn’t a basis for classification; color and replication speed aren’t meaningful taxonomic criteria.

Differences in the viral surface proteins and the host range determine how influenza is categorized. The main surface proteins, hemagglutinin and neuraminidase, come in multiple forms, and their specific combinations define subtypes (like H1N1 or H3N2). These surface proteins govern how the virus attaches to and enters cells and how the immune system recognizes the virus, which also influences which species can be infected. Because of this, grouping by these surface-protein differences and by host range best reflects how influenza is subdivided into subtypes and strains. Other ideas don’t fit: influenza is an RNA virus, so DNA content isn’t a basis for classification; color and replication speed aren’t meaningful taxonomic criteria.