Fig. 2

Classification of CTCF site clusters by relative orientation. CTCF mono-plet, di-plet, tri-plet and tetra-plet adjacent binding sites in all possible patterns of relative orientation. Patterns are divided into four classes: Same (all sites oriented in the same direction), Convergent (sites pointing towards each other), Divergent (sites pointing away from each other) and, for tri-plets and tetra-plets, the class Convergent + Divergent. The total number of patterns discovered from the complete set of CTCF binding sites in the human genome, independent of inter-CTCF site distance, is shown for each class. Note that the marginal sums of patterns along the columns are slightly different. This is because the number of k-plet patterns found in each chromosome arm (see the ‘Methods’ section) is equal to M − K + 1, where M is the total number of CTCF sites on that chromosome arm. Therefore, we have a discrepancy of 42 di-plets, 84 tri-plets and 126 tetra-plets relative to the mono-plets (see the ‘Methods’ section). p values are computed for di-, tri- and tetra-plets using the Pearson chi-square test. Effect sizes and significances were also computed by randomising the orientations of CTCF binding sites (see Additional file 1: Fig. S4)