DNA (deoxyribonucleic acid) is a molecule found inside cells. DNA is shaped like a spiral ladder. It carries the genetic instructions that help a cell develop and function. This genetic information is passed from parents to children. DNA helps determine what features a person inherits from their parents, including blood type, hair color, eye color, and other characteristics.

Chromosomes are parts of body cells that carry the DNA. The DNA of each chromosome is divided up into genes. Each person's DNA contains thousands of genes.

Changes (mutations) can occur in the DNA of genes. These changes may affect a person's risk for developing a disease. It also affects how people respond to medicines.