Deoxyribonucleic acid (DNA)
The chemical substance from which genes are made. DNA is a long, double-stranded helical molecule made up of nucleotides which are themselves composed of sugars, phosphates, and derivatives of the four bases adenine (A), guanine (G), cytosine (C), and thymine (T). The sequence order of the four bases in the DNA strands determines the genetic instructions for the development, functioning , growth and reproduction of all known organisms. Within eukaryotic cells, DNA is organised into long structures called chromosomes.