Chromatin is a substance within a chromosome consisting of DNA and protein. The DNA carries the cell's genetic instructions. The major proteins in chromatin are histones, which help package the DNA in a compact form that fits in the cell nucleus. Changes in chromatin structure are associated with DNA replication and gene expression.
Chromatin is the material that makes up a chromosome that consists of DNA and protein. The major proteins in chromatin are proteins called histones. They act as packaging elements for the DNA. The reason that chromatin is important is that it's a pretty good packing trick to get all the DNA inside a cell. If one took the DNA inside of one cell and stretched it out end to end, it would be about a yard long. Each cell is about a hundredth of a millimeter across, so it's pretty good packing job for the yard of DNA within something that is a hundredth of a millimeter in diameter. And the chromatin does that by wrapping and re-wrapping the DNA in a very tight coil. And that arrangement is called chromatin.