Setting up a polymerase chain reaction (PCR), Institute of Child Health, London, May 2000.
© Science Museum / Science & Society Picture Library
Some of the DNA in bones and teeth can last for many years after a person has died. Scientists can examine DNA from people murdered a century ago, or even from 3000-year-old ancient Egyptian mummies by using a PCR. PCR makes millions of exact copies of a piece of DNA in just under an hour or so, thus allowing scientists to extract DNA from tiny samples that would be too small for other methods.