Higher-order DNA compaction in a eukaryotic chromosome. This model shows the levels of organization that could provide the observed degree of DNA compaction in the chromosomes of eukaryotes. First the DNA is wrapped around histone octamers, then H1 stimulates formation of the 30 nm filament (solenoid model is shown). Higher levels of organization are not well understood but seem to involve further coiling and loops in the form of rosettes, which also coil into thicker structures. Overall, progressive levels of organization take the form of coils upon coils upon coils. In cells, the higher-order structures (above the 30 nm filament) are unlikely to be as uniform as depicted here.