Figure 2.

Plausible evolutionary trajectory for reordering of an essential gene in a potyvirus genome. First, the essential gene must be duplicated (variant a → variant b) to ensure that the virus can replicate autonomously at all times. Subsequently, we anticipate that one copy of the duplicate gene will be lost: either the second new copy is deleted (variant c) or the alternative gene copy is deleted (variant d). In the latter event, further evolution will take place to accommodate this reordered genome (variant e).