Deoxyribonucleic acid (DNA) is the genetic material that contains the instructions for an organism's development and characteristics. It is a molecule and polymer, which is made from smaller units called nucleotides. Each nucleotide consists of a nitrogen-containing nucleobase, a deoxyribose sugar, and a phosphate group. There are four different types of nucleobases that make up DNA: adenine (A), guanine (G), thymine (T), and cytosine (C). These nucleobases pair with each other in a specific way, with A always pairing with T, and G always pairing with C. The sequence of these nucleobases along the DNA molecule determines the genetic code, which is the set of instructions that guides an organism's development and characteristics. DNA is found in the nucleus of cells, and the genetic code is passed down from parents to offspring through reproduction.