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Primers

An important component of PCR is the primer(s), which are short sequences of DNA (typically 10-30 base pairs long) that help initiate the synthesis process and also determine exactly which region(s) of DNA will be amplified.

The design of primer sequences exploits the  complementarity property of the DNA molecule. In the example below, the sequence to be amplified (the "template") is shown in blue, and a possible primer sequence (18 bases in this case) is shown in red.

Keep in mind that the primer sequences can be located anywhere along the template sequence, but must flank the key area of interest.