Genetic code They looked for differences that would help separate the human sequence from the chimp sequence. Fujiyama's team found just 1.44% of the DNA was different at the level of single letters of genetic code. These letters, A, C, T and G, stand for the nucleotides that make up the DNA of all living creatures. The nucleotides match up to make amino acids, which in turn string together into genes that control the proteins made by cells. There are vast stretches of DNA that do not make up genes and scientists are struggling to understand their importance. Fujiyama's team...