Genes are segments of DNA (deoxyribonucleic acid) that contain the code for a specific protein. They are contained in chromosomes, which occur in the nucleus of the cell. Chromosomes are structures within cells that contain the genes. A chromosome is made up of a very long DNA strand that contains hundreds to thousands of genes. The genes are arranged in a specific sequence on each chromosome. Every single gene has a particular location on the chromosome. That location is known as its locus. In addition to DNA, chromosomes also contain other chemical components that play key roles in influencing gene function.