Fig. 1.

Different scales of intra-chromosomal 3D genome organization in human cells and their corresponding appearance in Hi-C interaction maps. A: Hi-C compartments (also known as A and B compartments) constitute the largest scale of organization and represent alternating active regions and inactive regions that each preferentially engage in homotypic interactions. B: TADs are sub-Megabase domains embedded within Hi-C compartments. Within a TAD, interactions are enriched over surrounding domains. TADs appear as triangles along the diagonal of the Hi-C map. C: DNA loops represent interactions between two genomic loci, e.g. an enhancer and a promoter (red and blue bars) or the two extremities of a TAD (purple bars). They appear as a punctuated increase of signal (black dots) within or on top of a TAD in a Hi-C map. Below each schematic Hi-C map, approximate length-scales are indicated. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)