Chromosomes are structures that package most of our DNA inside cells. People usually have 23 pairs of chromosomes, with one of each pair inherited from each parent. Changes in chromosome number or structure can affect development and health.

Browse the chromosomes to learn about their roles and related conditions. You can also explore mitochondrial DNA, a small separate set of genetic instructions found in the parts of cells that produce energy, and learn how its inheritance differs from that of DNA in chromosomes.