Genetic research. Computer artwork of part of a DNA molecule in a conical flask. DNA (deoxyribonucleic acid) is a double helix molecule that carries the genetic code, which controls and transmits an organisms hereditary traits. DNA is made up of two strands of sugarphosphate groups. The strands twist to form the double helix shape, and are crosslinked by complementary pairs of nucleotide bases (horizontal links). There are four types of nucleotide base: adenine, guanine, cytosine and thymine. The sequence of base pairs, arranged in discrete segments known as genes, determines the genetic code.