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(1992) Matt McCoy (front) and Mark Bodee extract DNA from fetal tissues and blood and semen stains at Cellmark Diagnostics in Germantown, Maryland. ). 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.