In 1983, Kary Mullis imagined copying DNA while driving through California at night: the idea transformed modern genetics forever

In 1983, while Kary Mullis was driving around Northern California, he got an idea to solve the decades-old frustration of molecular biologists regarding the ability to rapidly reproduce small amounts of DNA in large quantities. It occurred to him that by subjecting the DNA samples to repetitive heating and cooling cycles, along with using short artificial primers, the DNA strands would be able to separate and multiply exponentially, thus producing huge quantities of DNA. His insight eventually led to the development of the Polymerase Chain Reaction (PCR), which is among the most important laboratory techniques developed in modern times.

In an interview from the biography of Kary Mullis, who won the Nobel Prize, Mullis explained how the discovery struck him all of a sudden when he was driving through California at night. He explains how, at this point, he was working for Cetus Corporation, a biotechnology firm where scientists were already exploring DNA chemistry and techniques of genetic analysis. This discovery was important due to the fact that the methods for DNA analysis prior to PCR were extremely time-consuming and technically impossible because the sample size was not sufficient for genetic testing or sequencing. PCR transformed this by making it possible to amplify even small traces of genetic material into sizable samples in just hours instead of weeks. Although the technique may have appeared too simplistic for consideration at first, it proved itself fundamental in genetics, medical diagnostics, forensic studies, archaeology, tests of infectious diseases, and evolutionary studies.

PCR worked by turning DNA replication into a controlled repeating cycle

It works by heating up the DNA to separate strands, cooling the temperature to allow the primer to bind to the targeted sequence, and then synthesizing new DNA with complementary strands through enzymes. This cycle of doubling the amount of target DNA happens at every single cycle; thus, there is an exponential growth in the reaction process. As noted by the National Human Genome Research Institute, PCR had an impact on genetics by amplifying DNA from extremely minute biological samples such as blood spots, hair shafts, fossils, and pathogens.


A critical innovation in PCR involved the use of the heat-stable Taq polymerase enzymes isolated from the thermophilic bacteria that live in hot springs. With the ability to undergo repeated cycles without requiring constant manual replacement of enzymes, the technique evolved from a theoretical concept into a practical laboratory process. What made PCR a fast-growing technique was that its uses were not only confined to genetics. It also became essential in diagnosing diseases, criminal investigations, genealogy studies, cancer studies, and eventually, COVID-19 tests. As stated by Britannica, the Polymerase Chain Reaction (PCR) brought about exponential growth in the field of molecular biology.

The discovery permanently changed modern biology and medicine

PCR became so important that it became a cornerstone of many laboratory systems today. It completely revolutionized genetic research concerning inherited disease, pathogen identification, forensic analysis, and even ancient DNA studies. For his invention of PCR, Mullis was awarded the Nobel Prize in Chemistry in 1993. But the memory of the event will forever be marked by the unexpectedness of the occurrence itself. One of the greatest methods developed in modern times was born in the solitude of nighttime thinking by a scientist who was organizing a natural biological process into a reproducible chemical reaction.

The PCR is considered revolutionary because the method of rapid generation of accurate DNA copies changed the field of research in such a manner that experimental biology was no longer possible without it. What is even more interesting is the fact that such a scientific revolution can be achieved not by inventing some completely new material or device but simply by finding a better way to imitate a biological process that occurs naturally within any organism.