Cell-cycle dependence of chromosome structure. Left: high-resolution chromosome-conformation capture technologies have revealed that each mammalian chromosome territory can be decomposed into multi-megabase compartments where preferential interactions occur between active gene-rich and inactive gene-poor regions of the chromosome. Compartments can be further partitioned at the submegabase scale into topological associating domains (TADs) spanning a few hundred kilobases each. Dekker and colleagues  show that compartments and TADs are stable across the cell cycle from G1 to late S phase. Right: in metaphase, the compartment and TAD structures disappear and are replaced by a cylindrically condensed structure of linearly arranged short-range loops , which occur on a shorter genomic scale (80 kb on average) than TADs. It is hypothesized that the persistence of bookmarking factors on the mitotic chromosome might facilitate the rapid re-emergence of compartments and TADs upon exit of the cells from mitosis.