Percentage of overlapping genes in a given configuration (codirectional (a), convergent (b), divergent (c), see text) versus the percentage of consecutive genes in the same configurations to include non-overlapping genes. The dashed lines are the y = x lines and serves as a guide to the eye for testing the hypothesis that the two percentages are equal. The color code is red for Archaea and blue for Bacteria. The analysis is performed by considering only those overlapping genes annotated in the COG database. The arrows in each panel gives a visual representation of the different types of overlap. Magenta and green arrows indicate genes in the normal and complementary strand, respectively.