染色质：细胞核中较易染色的蛋白质，在细胞的非染色质中形成一个核纤丝网络。它是附着于蛋白质(主要是组蛋白)结构碱基的脱氧核糖核酸，是遗传基因的载体。它以两种染色性质不同而可互变的状态存在，即常染色质及异染色质，细胞分裂时卷曲折叠而形成染色体。
Levels of chromatin packing. This schematic drawing shows some of the orders of chromatin packing thought
to give rise to the highly condensed mitotic chromosome. The folding of naked DNA into nucleosomes is the best understood level of packing. The structures corresponding to the additional layers of chromosome packing are more speculative.