What is the major cause of antigenic drift?

• A. The mixing of RNA viral genomes from two different viruses.
• B. The mixing of viral proteins to form an entirely new virus.
• C. Mutations in RNA viral genomes caused by the replicase enzyme.
• D. Mutations in DNA viral genomes caused by the replicase enzyme.

Answer: (C)

Verified step by step guidance

1. Understand the concept of antigenic drift: Antigenic drift refers to the gradual accumulation of mutations in the viral genome, particularly in the genes encoding surface proteins, which can lead to changes in the virus's antigenic properties.
2. Identify the role of the replicase enzyme: In RNA viruses, the replicase enzyme is responsible for copying the viral RNA genome. This enzyme lacks proofreading ability, leading to a higher mutation rate during replication.
3. Recognize the impact of mutations: These mutations can alter the structure of viral proteins, especially those on the surface, which are recognized by the host's immune system. This can result in the virus evading immune detection.
4. Differentiate between RNA and DNA viruses: RNA viruses are more prone to mutations due to the lack of proofreading by their replicase enzymes, whereas DNA viruses generally have lower mutation rates because of more accurate replication mechanisms.
5. Conclude the major cause: The major cause of antigenic drift is the accumulation of mutations in RNA viral genomes, primarily due to the error-prone nature of the replicase enzyme during viral replication.