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Every species has slight differences in their DNA sequences; even closely related species have some areas of their genome that are unique. By isolating the unique sequence in a species’ DNA sequence, scientists can create molecular tests that specifically identify the presence of that organism.
Scientists take a sample of tissue and use the Polymerase Chain Reaction (PCR) to multiply DNA at the site of the unique sequence. This is then analysed on a gel, which separates pieces of DNA by their size. If the unique sequence is not present, the DNA will not be multiplied and no band will appear on the gel. However, if the sequence, and therefore the organism, is present, a band will be seen.