DNA analysis, negative image. Graphs showing the results of DNA (deoxyribonucleic acid) sequencing. A DNA molecule consists of two sugar-phosphate backbones, arranged as a double helix, joined by nucleotide bases. There are 4 types of nucleotide base; adenine (A), cytosine (C), guanine (G) and thymine (T). Sequences of these bases make up genes, which encode an organism's genetic information. Uses of DNA sequencing include; finding genes responsible for disease, DNA fingerprinting and paternity testing.