The correlations between ROL values is not driven by broad differences among different functional classes of genes or differences between essential and nonessential genes. For each functional class (as defined by MultiFun [3]) the parametric and nonparametric correlation coefficient between the ROL for nonessential orthologous genes in the γ-β-proteobacteria, α-proteobacteria, and Bacilli-Mollicutes was calculated. Only MultiFun classes for which ROL values existed for at least 20 genes are shown. Several functional classes are abbreviated, as follows: Inform., Information transfer (Class 2); Reg., Regulation (Class 3); Process, Cell processes (Class 5); Structure, Cell structure (Class 6); Location, Location of gene products (Class 7); genetic unit, genetic unit regulated (3.3); primary transport, primary active transporters (4.3); electrochemical transport, electrochemical potential driven transport (4.2); prophage and phage related, prophage genes and phage related functions (8.1). Error bars were calculated by bootstrapping pairs of ROL values within each class 1000 times [15]. A) Parametric correlation coefficients between γ-β-proteobacteria and α-proteobacteria ROL values for each functional class. B) Nonparametric correlation coefficients (Spearman's ρ) between γ-β-proteobacteria and α-proteobacteria ROL values for each functional class. C) Parametric correlation coefficients between γ-β-proteobacteria and Bacilli-Mollicutes ROL values for each functional class. D) Nonparametric correlation coefficients (Spearman's ρ) between γ-β-proteobacteria and Bacilli-Mollicutes ROL values for each functional class.