Genetic code. Conceptual computer artwork of the individuality of DNA showing a hand overlaid with a DNA molecule, letters forming the genetic code and a bar code. Each individual has a slightly different genetic code, made up of the sequence of four bases in DNA (deoxyribonucleic acid). These are adenine (A), thymine (T), guanine (G) and cytosine (C). The bases form the links between the two sugar-phosphate strands in DNA's double helix. DNA is found in all living things and controls growth and development.