Also known as deoxyribonucleic acid, DNA is a long molecule that contains our unique genetic code (hereditary material) found in most organisms, most notably humans. The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The order, or sequence, of these bases determines the information available for building and maintaining an organism. It is a two-stranded molecule with a unique ‘double helix’ shape. The human genome is made of 3.2 billion bases of DNA but other organisms have different genome sizes. An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.