Fig. 1

Histograms of Kr for various sets of site-genome pairs. There are 41 equal bins at the segment [0; 2), the percent of site-genome pairs with Kr falling into a bin is shown over its middle. a Blue dotted line shows the distribution for actual pairs of orthodox R-M-systems; green dashed line is for the subset of orthodox site-genomes pairs of the prokaryotic control set; red solid line is for the similar subset of the viral control set. b Blue dotted line shows the distribution for actual pairs of R-M-systems of types I, IIC/G, and III together; green dashed line is for the subset of non-orthodox site-genomes pairs of the prokaryotic control set; red solid line is for the similar subset of the viral control set. In both cases the cutoffs for under- and overrepresentation are shown by solid vertical lines