Every living thing is made up of tiny building blocks called cells. Inside the cells is a special code called DNA that tells the cells how to build and function. DNA stands for deoxyribonucleic acid. It’s like a long, twisted ladder and it’s made up of four different chemicals called nucleotides: adenine, cytosine, guanine, and thymine. These nucleotides pair up in a specific way (A always pairs with T, and C always pairs with G), and this pairing is what makes up the genetic code.

Every person has two copies of each gene, one from each parent. Some genes determine things like your eye color or height, while others can contribute to things like diseases. The study of genes is called genetics, and scientists can use this information to learn more about how traits are passed down from generation to generation.