What is the workflow of the Sanger Sequencing method?

There are 3 main steps involved in the workflow of the Sanger Sequencing method. 

1. In the first step, the DNA sequence of interest is used as the template for chain-termination PCR. Modified nucleotides (ddNTPs) are added in low ratios alongside regular nucleotides during this type of PCR. Since ddNTPs lack the 3'-OH group necessary for bond formation, DNA polymerase randomly incorporates them causing the extension to stop. In automated Sanger sequencing, all four types of ddNTPs are combined in a single reaction and each dNTP is uniquely labeled with a fluorescent tag. In manual Sanger sequencing, four separate PCR reactions are prepared, each incorporating a single type of ddNTP (ddATP, ddCTP ddGTP, and ddTTP). 
2. During the second step, chain-terminated oligonucleotides undergo size separation through gel electrophoresis. In this process, DNA samples are loaded into one end of a gel and an electric current is applied. Due to the negative charge of DNA the oligonucleotides move towards the positive electrode on the opposite gel end. Since all DNA fragments share the same charge per unit of mass, their speed is dictated exclusively by size. Smaller fragments encounter less friction and thus move faster. Consequently, oligonucleotides arrange themselves from smallest to largest and the gel is read from bottom to top. In automated Sanger Sequencing, all oligonucleotides are exposed to a single capillary gel electrophoresis within the sequencing machine. In manual Sanger Sequencing, oligonucleotides from each of the four PCR reactions are run in separate lanes of the gel. This segregation allows one to associate each oligonucleotide with its correlating ddNTP. 
3. Lastly, the gel is analyzed to identify the sequence of the input DNA. DNA polymerase synthesizes DNA only in the 5’ to 3’ direction from a given primer. Thus, each terminal ddNTP in the chain-terminated fragments correlates to a specific nucleotide in the original sequence. By examining the gel bands from smallest to largest, the 5’ to 3’ sequence of the original DNA strand can be identified. In automated Sanger Sequencing a computer reads each band of the capillary gel, utilizing fluorescence to identify each terminal ddNTP. More specifically, as each fragment reaches the end of the tube, the laser illuminates it, allowing detection of the attached dye. With unique fluorescent labels for each ddNTP, the emitted light directly exhibits the terminal ddNTP's characteristics. The result is a chromatogram that displays fluorescent peaks for each nucleotide along the template DNA's length. In manual Sanger Sequencing one should read all four lanes of the gel simultaneously (moving from bottom to top); the lane helps determine the terminal ddNTP for each band.