A chromosome (from the Greek khroma : color and soma : body, element) is a structure made up of DNA surrounded by proteins. Each chromosome has a different shape, either rod or chevron. We have 23 pairs in the nucleus of each of our cells. Chromosomes are particularly visible at the time of cell division and are in different numbers depending on the species. The number of chromosomes varies in certain types of diseased cells, especially in cancer cells, where in general, it increases.