An abbreviation of DeoxyriboNucleic Acid, a molecule vehicle for storing and passing on hereditary genetic information. In human beings, they are located within the cells’ nuclei. Unwound, DNA molecules stretch out in a very long line made up of a precise chain (sequence) of base structural units called nucleotides. Each nucleotide is made up of a base (the bars of the helix), a sugar and a phosphate (the verticals of the helix). The structure of DNA, made up of the two complementary strands of a rolled up helix (double helix), allows it duplicate itself into two molecules which are identical to each other and identical to the mother gene when they are replicated or duplicated. DNA is one of the component parts of chromosomes. Genes are segments of DNA.