Polymerase chain reaction (PCR) drawing by Mullis, 1992. This ground-breaking technique for amplifying DNA (deoxyribonucleic acid) in genetic research was invented by US biochemist Kary Banks Mullis (1944-2019). He invented PCR in 1983, and shared the 1993 Nobel Prize in Chemistry for this work. The purple and red horizontal lines represent strands of DNA being copied. The 'dNTPs' at the top of the page refer to the nucleotide bases that make up a DNA strand, here labelled with the letters TAGC: thymine (T), adenine (A), guanine (G) and cytosine (C). Mullis drew this diagram on 15 May 1992 as part of a set of oral history interviews (see C048/5121) for the Smithsonian's National Museum of American History.