First Generation Sequencing

First Generation Sequencing, also known as Sanger sequencing, refers to the chain-termination method that was developed by Fredrick Sanger and co-workers in 1977 (figure below). The DNA molecule is amplified with modified nucleotides (ddNTP), and the addition of only one base per cycle is allowed. The DNA is then amplified with varying length: each strand is one base pair longer than the previous molecule. These molecules are then separated by capillary electrophoresis. Due to the fluorescent dye at the end of each fragment, we are able to identify the base (A, G, T, or C) by reading the different color signal.

On the left, a depiction of a gel showing the separation of many DNA molecules by length of nucleotides, each molecule is shown one of 4 colors correlating to the 4 DNA nucleotides. On the right, for each band of DNA is a horizontal colored peak of the same color.

Chain-termination method. The labeled DNA molecules are separated according to their size. Each molecule has a modified nucleotide (ddNTP) that is labeled with a fluorescent dye. Each different fluorescence color indicates a specific base: Green (A), yellow (G), red (T) and blue (C).

Read more about Next Generation Sequencing.