Figure 2
From: Evolutionary constraints permeate large metabolic networks
Many reactions show constrained pairwise evolution. a) The horizontal axis shows the negative decadic P-value of the statistical association of two reactions, as determined by an exact binomial test (see Methods). The left vertical axes shows the proportion of reactions that are positively associated, that is, that co-occur more often than expected by chance alone. The right vertical axis shows reactions with negative associations, reactions that occur less often together than expected by chance alone. Note the difference in scale for the two vertical axes. The Bonferroni-corrected value of P = 0.05 (0.05/(1.35 × 107)) lies at -log10(P) = 8.43. b) The vertical axis shows the mean and standard deviation (length of bars) of the number of genomes that harbor only one but not both reactions of a positively associated reaction pair. Specifically, if two reactions are encoded by n1 and n2 genomes, and if n12 genomes encode both reactions, then the vertical axis shows the quantity 1-(n12/(n1+n2-n12)), averaged over all reaction pairs whose P-value lies in a given range (horizontal axis).