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Genetic sequence. Computer illustration of a gene- tic sequence and bar codes. DNA (deoxyribonucleic acid) contains the genetic code as a sequence of 4 molecules called nucleotide bases: adenine (A), cytosine (C), guanine (G) and thymine (T). Like DNA, bar codes contain digital information, in their case represented by lines of varying thickness. DNA encodes, transmits and controls the development of an organism's hereditary traits. (KEYSTONE/SCIENCE PHOTO LIBRARY/PASIEKA)