GENETICS, DNA. GENETICS, DNA DNA, deoxyribonucleic acid, is composed of two long chains of molecules. Each chain contains deoxyribose in alternation with phosphoric acid connected to four nucleotides: adenine, thymine, cytosine, guanine. The two chains wind around each other forming a double helix, the backbone of the chromosomes. Successive segments of the DNA molecule form genes which carry the hereditary information transmitted from generation to generation. Schematic representation of the