Chromatin is divided into heterochromatin (condensed) and euchromatin (extended) forms. Hetrochromatin is composed mostly of satellite DNA tandem repeats. The active components of chromatin are DNA and histone proteins, although other proteins also occur. The functions of chromatin are:
- to package DNA into a smaller volume to fit in the cell
- to strengthen the DNA to allow mitosis and meiosis
- to control DNA replication and gene expression. Exactly how this is done is not yet clear.