proportion of the different mutation types scored among molecular clones of FMDV populations. Each mutation type (abscissa) was counted for the indicated populations by comparing the nucleotide sequence from each individual molecular clone with the consensus sequence of the corresponding population. The populations analyzed are those derived from FMDV MARLS (top left panel), from populations passaged in the absence of drug and derived either from C-S8c1 or MARLS (top right panel), or from FMDV C-S8c1 (bottom panels). The populations correspond to those depicted in Figure 1, and can be identified according to the drug treatment (AZC, azacytidine; FU, 5-fluorouracil; R, ribavirin; no drug and C populations, control populations passaged in the absence of drug). Note the difference scale in ordinate of the top versus bottom panels. The genomic regions and number of nucleotides analyzed for each population are described in Table 1. Procedures for nucleotide sequence determination and bioinformatic analysis of sequences are detailed in Methods.