DNA sequencing was invented in the UK by double-Nobel-prizewinning scientist Fred Sanger. It relies on the natural ability of DNA to copy itself, using a builder enzyme. The builder enzyme makes many partial copies of a piece of DNA. Copying is halted at either an A, C, G or T base. Scientists carry out DNA sequencing by repeating this process in four separate test tubes - one with copies stopped at all the As, one at the Cs, one at the Gs and one at the Ts.