Figure 1.

Quasispecies replication dynamics of RN A viruses. The central scheme represents a characteristic heterogeneous distribution of genomes. Each line represents a genome with mutations depicted as symbols. Average consensus sequence is depicted below the mutant spectrum. The central initial population can evolve towards increased fitness (on the right) when replication takes place with high population size. When the population undergoes bottlenecks (on the left) the fitness of the population drops by the action of Müller’s ratchet. Virulence evolution follows an independent trajectory from the one observed for relative fitness; low fitness viruses can have a high virulence phenotype.