The chromosomes of a cell are in the cell nucleus. They carry the genetic information. Chromosomes are made up of DNA and protein combined as chromatin. Each chromosome contains many genes. Chromosomes come in pairs: one set from the mother; the other set from the father. Cytologists label chromosomes with numbers. Chromosomes are present in every cell nucleus with very few and special exceptions. This means they are found in all eukaryotes, since only eukaryotes have cell nuclei. When eukaryote cells divide, the chromosomes also divide.
When a body cell (such as a muscle cell) divides, the process is called mitosis. Before mitosis, the cell copies all the chromosomes and then it can divide. When they duplicate, chromosomes look like the letter "X". When they are doubled, the two halves are called chromatids. The chromatids are joined at the centromere.