Figure 3. Molecular mechanisms for generating viral diversity.

Viruses have evolved three main mechanisms for generating diversity on replication. (a) During replication, single point mutations are incorporated into one or more genomic positions as a result of a lack of proofreading activity of the viral polymerase. (b) During recombination, foreign genetic material is incorporated into the viral genome through mechanisms such as template switching during replication. (c) During reassortment, which occurs on dual infection of a cell with segmented genome viruses, whole gene segments can be swapped. All three mechanisms, which are not exclusive, may result in viruses that have new biological properties, such as new host range and pathogenic potential.