Structures found in the nucleus of the cell, which are visible under a microscope and which contain genetic (inherited) information. Human cells contain 46 chromosomes, which come in pairs. There are twenty-two pairs of chromosomes which are referred to as autosomes, because they do not determine the sex of an individual. The twenty-third pair are referred to as the sex chromosomes, and are called the X and Y chromosomes. Each chromosome contains thousands of individual genes, which will in turn determine an individual's characteristics.