DNA is a molecule inside nearly every cell of your body that contains the instructions for building and running you. DNA helps determine whether you'll have brown eyes or blue, straight hair or curly, and influences thousands of other traits from your height to the shape of your ears.

Think of DNA as an incredibly detailed instruction manual written in a special code. This code is made up of just four chemical letters (scientists call them A, T, G, and C), but arranged in different sequences, these letters spell out everything needed to create a human being. You inherited half your DNA from your mother and half from your father, which is why you might have your dad's nose and your mom's smile.

The letters DNA stand for deoxyribonucleic acid, but everyone just says DNA. Scientists discovered its twisted ladder shape, called a double helix, in 1953. Since then, understanding DNA has revolutionized medicine, helped solve crimes, allowed us to identify ancient remains, and helped scientists learn about long-extinct creatures.

Every person's DNA is unique (except for identical twins, who share the same DNA). This uniqueness makes DNA useful for identifying people, which is why investigators collect DNA evidence at crime scenes. Your DNA is like a biological fingerprint that's extremely hard to fake or change.