Phylogenetic analysis of the virus genomes isolated from bacteriophague Qβ populations evolved in the presence of AZC. Different colours are used to distinguish the genomes from each population included in the analysis: green for Qβ-AZC(t60), pink for Qβ-AZC(t70), and orange for Qβ-AZC(t90). Virus genomes corresponded to those shown in Table 1 and Additional file 1, and are identified using the same notation. The tree was derived by maximum likelihood methods (PhyML, program seaview 4)  using the sequence of the wild type virus to root the tree. Numbers at each node represent the bootstrap value (carried out with 100 replicates). Clusters described in the main text are highlighted, and the mutations common to all the genomes included in each one are also indicated.