Regional pairing brings chromosome territories close together.

3D representation of stacks of confocal images from ES cells. Green: chromosome 7 painting, red: DNA FISH with a probe covering KvDMR near the distal end of chromosome 7, white: DNA FISH with a probe covering Kcnn4 25 Mb away from the proximal end of chromosome 7. FISH signals are mostly located in or close to the edge of their chromosome territory. Most nuclei display two separate chromosome 7 territories (A). When KvDMR signals are close together, the territory arrangements can be ‘touching’ (B) with the proximal ends pointing away from each other, ‘Y-shaped’ with a larger region aligning (C), or ‘aligned’ with most of the chromosome being parallel (D). These arrangements occur with very similar frequencies (n = 9, 8, 9, respectively).