Figure 1. The organization of the eukaryotic genome.

Genomes are organized at multiple levels. DNA is wrapped around the nucleosome, which is made up of an octamer of core-histones, forming the chromatin fiber which folds into loops, often bringing upstream gene regulatory elements (yellow), such as enhancers, into proximity to genes (blue) to control their transcription (black arrow). The fiber then folds into chromatin domains, referred to as topologically associating domains (TADs), which associate with each other to create chromatin compartments. The DNA of each chromosome occupies a distinct volume, or chromosome territory (multiple colors), within the cell nucleus, generating non-random patterns of chromosome and gene locations. In the DNA-free space, the nucleus also contains RNA and proteinaceous protein aggregates which form nuclear bodies (blue).