The chemical inside the nucleus of a cell that carries the genetic instructions, or code, for making and maintaining living organisms. DNA consists of two long chains of chemical groups or bases, twisted together in pairs to form a double helix. The bases are the "letters" that spell out the genetic code. In DNA, the code letters are A, T, G, and C which stand for the chemicals adenine, thymine, guanine, and cytosine, respectively.
Determination of the order of bases in a DNA molecule.