Chromosomes are part of most types of cells in the body. Each chromosome has a single molecule of DNA.

Humans have 46 chromosomes (23 pairs). Half of a person's chromosomes come from the mother and half from the father. One of the 23 pairs are the sex chromosomes, X and Y. A female inherits an X chromosome from each birth parent (XX). A male inherits an X chromosome from their mother and a Y chromosome from their father (XY).

Changes in chromosomes can cause problems with how the body works. They can cause a genetic condition, such as Down syndrome.