DNA. Computer illustration of a molecule of DNA (deoxyribonucleic acid), the genetic material found in all living cells, and genetic sequences. This is alpha DNA, the rarer form of DNA, which spirals anti-clockwise when seen from above. DNA encodes and controls the hereditary traits of living organisms. It is a double helix (purple) connected by paired nucleotide bases (red, yellow, green & blue). The sequence of these bases determ- ines the unique genetic code of each person. Each band in the autoradiograms (right) represents the position of one of the bases in the code. At left letters represent the sequence of bases: adenine (A), thymine (T), cytosine (C) and guanine (G).