Figure 3. Evolutionary conservation and relative gene orientation.

For a range of evolutionary distances within an interval of 0.01 units the number of gene pairs corresponding to a certain relative gene orientation was calculated and plotted. Gene orientation considered were divergent (← →), convergent (→ ←) and co-directional (→→). Cumulative counts of gene pairs are shown. Randomized counts were obtained by shuffling for every species the identities of OrthoMCL clusters or Pfam groups. Based on these results of randomizations it would seem that the probability of finding a pair of genes with the same relative orientation in at least two different species by chance only is approximately 0.002–0.01. A. Genes clustered using OrthoMCL. B. Genes grouped on the basis of Pfam architectures.