Sequencing

Sequencing reads the exact order of letters - As, Cs, Ts and Gs - along a segment of DNA. Large-scale sequencing involves two stages: the first is to set up the sequencing reaction and the second is to read the results.

The Sanger sequencing reaction (invented in the 1970s by Nobel Laureate Fred Sanger) is a chemical method of reading the order of DNA letters. This was the method used to sequence the human genome. The reaction is a slightly altered version of the process your cells go through when they divide and have to make a copy of your DNA.

In the Sanger sequencing reaction, we effectively replace each of the four DNA letters with a modified letter with a coloured label attached. We tag each A with a green label, each G with a yellow label, each T with a red label and each C with a blue label. The labelled DNA is then run past a laser that detects the different colours and the order they pass.