DNA (Sanger) sequencing using
dideoxy chain termination.
A primer is annealed to the target template DNA.
A mixture with DNA polymerase, the four dNTPs, and one
dideoxynucleotide (such as ddATP), is added.
During primer extension, the polymerase occasionally inserts a
ddNTP instead of a dNTP, which lacks the 3'-OH needed to attach
the next nucleotide, terminating the chain.
Gel electrophoresis separates the synthesized fragments that
terminate at the dideoxynucleotide.