Question: When and why does a mutation in a virus happen?

Olivia Edwards answered on 8 Jun 2020:

Hi Paulina!

Mutations can happen for a lot of different reasons, and can be caused by specific substances (for example UV light which can cause skin cancer by causing a lot of mutations to accumulate in skin cells). Mutations also occur as a part of DNA replication. For example when a virus duplicates itself, it will need to copy all of its DNA. When all of the DNA is copied, mistakes can be introduced and this can lead to a mutation (i.e. a change in the DNA sequence). Sometimes these mistakes will be recognised and fixed, but sometimes they will go un-noticed!

Usually DNA replication is very accurate, but these sequences can be very, very long, meaning that a mistake is more likely to occur. Viruses also replicate themselves A LOT, which means that these mistakes are likely to happen at some point. The rate at which a virus mutates will therefore depend on how often it replicates and how much DNA it contains. We can’t be sure when a mutation will happen, but we can estimate how often mutations occur in a virus by comparing the sequences of different virus particles.