In Sanger sequencing, the DNA to be sequenced serves as a template for DNA synthesis. A DNA primer is designed to be a starting point for DNA synthesis on the strand of DNA to be sequenced.

After the primer is in place on a single, unwound polynucleotide strand, DNA polymerase wraps itself around that strand, and it attaches new nucleotides to the exposed nitrogenous bases.

A DNA primer is a single-stranded piece of DNA of known sequence, generally about 20 bases long, that will initiate the building of a new DNA strand that is complementary to the cloned DNA.