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MODEL RELEASED. Genetic code. Conceptual computer artwork of a DNA double helix (white) with nucleotide base sequences (letters, down centre), a woman's face and binary code (zeros and ones). A DNA (deoxyribonucleic acid) helix is composed of two twisting sugar-phosphate molecules linked by pairs of bases. The sequence of base pairs determines the genetic code, the instructions that control and transmit an organism's hereditary traits. There are four types of base: adenine (A), cytosine (C), guanine (G) and thymine (T). Binary code is another method of storing information. (KEYSTONE/SCIENCE PHOTO LIBRARY/MEHAU KULYK)