Genetic research. Coloured sample tubes containing nucleotide bases that make up deoxyribonucleic acid (DNA). The clear tubes contain reaction mixtures. These stoppered sample tubes are cooled on ice. The four nucleotide bases of DNA are adenine (A), thymine (T), guanine (G), and cytosine (C). Sequences of these base molecules form the genetic code in DNA, a code of inherited characteristics necessary to make an organism. The exact properties of the DNA molecule depends upon the sequence of these bases within it. DNA research includes the mapping of genes associated with genetic diseases, and genetic fingerprinting in forensic studies of criminals.