DNA sequencing. Computer screen showing a sequence of base pairs forming part of the human genetic code. The three billion base pairs that form the genetic code of human DNA (deoxyribonucleic acid) are collectively known as the human genome. Each of the coloured bands represents the position of one of the four nucleotide bases that form the code. As each persons genetic code is unique this sequence is called a DNA fingerprint. Photographed at the Joint Genome Project (JGI), part of the Human Genome Project, in Walnut Creek, California, USA.