All GeneChip microarrays take advantage of the natural chemical attraction between DNA molecules. There are only four molecules, or "bases", in every DNA chain: adenine (A), guanine (G), thymine (T) and cytosine (C). These four molecules partner: C partners with G and T partners with A. Pairing is a natural state for DNA and if you pulled the double helix apart, it would inevitably move back together, like two long chains of magnets that are attracted to each other.