The not-so-infinite malleability of RNA viruses: Viral and cellular determinants of RNA virus mutation rates
Mutations generated via virus- and cell-dependent mechanisms can differentially impact viral fitness. Viruses are depicted as colored spheres corresponding to the presence of beneficial, neutral, deleterious, or lethal mutations. Population size is depicted by the diagonal arrow and increasing square size. High mutation rates result in a phenotypically diverse viral population (“mutation rate” panel), but the frequency at which these variants appear in a population (“mutation frequency” panel) depends upon genetic drift and natural selection. As such, large population sizes are critical for buffering the viral population against the effects of deleterious and lethal mutations. The ratios of beneficial, neutral, deleterious, and lethal mutations are based on data from vesicular stomatitis virus (VSV) .