Figure 1.

Viral genetic diversity is the basis of natural selection and viral evolution. All viruses mutate over time. Mutations that are disadvantageous or that come at a cost to viral fitness are selected against. Mutations that confer a fitness advantage, especially in the presence of a selective pressure (represented by the horizontal dotted line), will be more likely to persist in future generations. This figure appears in colour in the online version of JAC and in black and white in the print version of JAC.