Figure 2.

Substitution frequency at nonsynonymous and synonymous sites plotted by genes present in different numbers of species. The nonsynonymous substitution frequency (dN) values were plotted against the synonymous substitution frequency (dS) values for (a) R7 core genes and strain-variable open reading frames (ORFs) present in two to seven species and (b) core genes and strain-variable ORFs present in seven species that are longer than one kilobase in size.