If you thought DNA was made of just A, T, G and C-- think again. Scientists have been expanding these options, and the resulting organisms could create the impossible. The genetic code that creates all life on Earth consists of four nucleotide bases: Adenine, Thymine, Cytosine, and Guanine. In the double-stranded helix of DNA, these bases pair up with each other in a certain way. In recent years, researchers have been able to expand the genetic code with new, synthetic bases.