DNA sequencing is the process of determining the sequence of nucleic acids containing four nucleotides (adenine, guanine, cytosine, and thymine). Early DNA sequencing methods included using chain termination inhibitors for DNA sequencing and chemical degradation for DNA sequencing. Subsequently, in the 1990s, several sequencing methods were developed, collectively known as next-generation sequencing (NGS sequencing), including Sanger sequencing (Chain termination), Large scale sequencing and de novo sequencing, basic methods of Shotgun sequencing, and high-throughput methods such as Single molecule real time (SMRT) sequencing and Illumina (Solexa) sequencing. DNA sequencing has become an important foundational technology in fields such as the Human Genome Project and basic biological research.

                                                 Fig 1: History of sequencing technology. (Wikipedia)

Sanger sequencing is a DNA sequencing method based on the random insertion of double deoxyribonucleotides (ddNTP) terminated by DNA polymerase during the DNA replication process. The chain termination nucleotide lacks the 3 '- OH group necessary for the formation of the phosphodiester bond. When ddNTP is incorporated, DNA polymerase will stop DNA extension, and ddNTP can be radiolabeled or fluorescent labeled for detection, and then separated by gel electrophoresis to read the sequence from the gel image. Although it has been replaced by next-generation sequencing with technological development, it can meet the requirements of small-scale and deep sequencing results with low error rates.

Single stranded DNA template, primers, DNA polymerase, normal deoxyribonucleotide triphosphate, and labeled deoxyribonucleotide triphosphate.