Human cloning. Conceptual computer artwork of two identical female faces representing human cloning. Part of the double helix of the DNA (deoxyribonucleic acid) molecule runs down centre. The sequence of the nucleotide bases of this molecule forms a unique genetic code that controls the individual development and functioning of every living organism. The code has four units, the bases adenine (A), guanine (G), cytosine (C) and thymine (T). Their sequence can be obtained in the form of an autoradiogram (bands at left) and written using the letters ACTG (right). Clones are genetically-identical copies that are created using genetic material from a template person.