(1992) Alison Thomas loading gel and putting a lid on a gel tank at Cellmark Diagnostics, England's first commercial DNA fingerprinting lab. DNA consists of two sugar- phosphate backbones, arranged in a double helix, linked by nucleotide bases. There are 4 types of base; adenine (A), cytosine (C), guanine (G) and thymine (T). Sequences of these bases make up genes, which encode an organism's genetic information. DNA Fingerprinting. MODEL RELEASED.