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MODEL RELEASED. Genetic code. Conceptual computer artwork of a DNA double helix (on white strip) with a woman's face and binary code (zeros and ones). A DNA (deoxyribonucleic acid) helix is composed of two twisting sugar-phosphate strands linked by pairs of nucleotide bases (red arrows). 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)