Question

Why do viral genomes change often, although gradually (genetic drift).

Answer 1

Viral genomes are made of genetic material. This genetic material undergoes duplication via enzymes called polymerases. Llike any enzyme, these enzymes are also error-prone. Hence, after replication, the viral genomes undergo changes. Most of these changes will be useless and might even result in loss to the viral success.

However, certain random changes will provide the virus an advantage. Also, certain mutations can allow the virus to infect a new unrelated host. This will allow the virus to infect a new host and thereby allow it to replicate more. Naturally such mutations will be selected for thereby resulting in the viruses gradually drifting off.