Genetic code. Computer artwork of a DNA (deoxyribonucleic acid) double helix with letters (down centre) representing the genetic code. The helix molecule contains the code, which controls and transmits an organism's hereditary traits. The helix is composed of two twisting strands (white) of sugar-phosphate molecules, linked by complementary pairs of nucleotide bases (not seen). There are four types of nucleotide base; adenine (A), guanine (G), cytosine (C) and thymine (T). The sequence of base pairs, arranged in discrete segments known as genes, determines the genetic code. Binary code (zeros and ones) is another method of storing information.