Genes are packaged into structures called chromosomes. Chromosomes come in pairs, and there can be hundreds and even thousands of genes on one chromosome. Every cell in the body has a total of 46 chromosomes, each with 23 pairs. Half of a person’s chromosomes come from the egg and the other half from sperm. The first 22 pairs of chromosomes are referred to as autosomes because they are the same between males and females. The 23rd, and final, pair are called sex chromosomes because these determine biological sex. Males have an X and a Y chromosome while females have two X chromosomes.