Chromosomes are made up of DNA and protein. The proteins are histones, and the DNA is wrapped around the histones. The nucleus of every cell contains chromosomes. In humans, there are 23 pairs of chromosomes in each cell; a pair of chromosomes is made up of one chromosome from each parent.
Until a cell begins to divide, chromosomes are not visible to the human eye. As cell division begins, the DNA compacts around the histones, becoming packed together in such a way they can be seen under a microscope. DNA is made of four base chemicals, cytosine, guanine, adenine and thymine. Each base pairs with another to form the twisted strands called a double helix.
Adenine pairs with thymine, and cytosine pairs with guanine. It is the sequence of the parings that gives each person certain traits. Histones are necessary to allow DNA to fit into the nucleus of a cell. If the DNA did not wind around the proteins, it would be too long. The histones give the chromosomes their shape and keep them compacted. Histones are negatively charged, attracting and binding to the positively charged DNA molecules. Eight proteins make up one histone core. Two hundred DNA base pairs are wrapped around one core.