7. Polymerase Chain Reaction (PCR)
Most genes have only 1 or 2 copies in the genome. If we want to look at the way evolution has affected a particular gene, we first have to isolate this gene from the tens of thousands of others that are present in each cell. One way of doing this is to use a technique called the Polymerase Chain Reaction (PCR) to amplify millions of copies of the gene that we want to study.
In this technique, the two strands of the DNA are separated by heating. Short strands of DNA called primers are stuck to each end of the gene. A protein called DNA polymerase is used to extend the primer along the sequence of the gene so that a copy is formed. This cycle is repeated 25-45 times with the number of gene copies doubling with each cycle. After the reaction has been carried out, some of it is run on a gel to check that the correct gene has been amplified.
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