Polymerase Chain Reaction 1983 – A Printing Press for Genetic Material

In 1983, while driving on a California highway, the biochemist Kary Mullis came up with an idea for copying a microscopic strand of genetic material billions of times. The process has since been used in countless medical applications. The idea, polymerase chain reaction (Polymerase Chain Reaction – PCR), became a billion-dollar industry, but Mullis received a bonus of only 10,000 dollars from his employer. Perhaps the Nobel Prize he received a decade later was a tremendous consolation prize.

Scientists generally need a certain amount of the genetic sequence of DNA to work with. However, the groundbreaking PCR technique can start with as little as a single DNA molecule in a solution, with the help of Taq polymerase, an enzyme that copies DNA and remains intact as the solution's temperature rises. (Taq polymerase was isolated from a bacterium taken from a hot spring in America's Yellowstone National Park.) Primers are also added to the mixture; these are short DNA segments that bind to the sample DNA at positions before and after the sequence under investigation. 

During repeated heating and cooling cycles, the polymerase quickly begins making more and more copies of the sample DNA between the primers. Thermal cycling allows DNA strands to separate and come back together repeatedly as needed for copying. 

PCR is used in many areas:

• Detecting foodborne pathogens
• Diagnosing genetic diseases
• Assessing levels of HIV in patients with AIDS
• Paternity testing
• Identifying criminals from traces of DNA left at a crime scene
• Studying DNA in fossils

PCR has also played a major role in advancing the Human Genome Project.

The medical journalist Tabitha Powlege writes:

“PCR does for genetic material what the invention of the printing press did for written material: it makes copying easy, inexpensive and accessible.” 

The New York Times describes Mullis's invention this way:

“It divides biology into two eras: before PCR and after PCR.”

Historical Figures Mentioned in the Article: Kary Banks Mullis (b. 1944)

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