What is the method of Sanger sequencing?

In Sanger sequencing, the sequencing reaction takes place in four different tubes. each tube contains a primer, dNTPs and a DNA polymerase. each tube also contains a different radiolabelled dideoxy nucleotide (either ddATP, ddTTP, ddCTP or ddGTP) (at a very low concentration). when this ddNTPs is incorporated into the sequence, the reaction stop. the incorporation of the ddNTP is a random process. this means that the mixture will contain several DNA fragments of different lengths. when the length of the fragment is known (through gel electrophoresis), the location of the radiolabelled ddNTP can be estimated and the entire strand can be build.