Sanger sequencing

Sanger sequencing is the original, gold-standard way of reading DNA, named after the scientist Frederick Sanger. The clever trick is to copy the DNA but occasionally stop the copy short at a known base, producing a ladder of fragments of every possible length that, read in order, spell out the sequence.

In the method, DNA polymerase copies a template, but the reaction mix also contains special chain-terminating bases that halt the copy whenever one is added. Each terminator carries a distinct fluorescent color, so when the resulting fragments are sorted by length, a machine reads off the colors in order and reconstructs the exact sequence.

Sanger sequencing is highly accurate and reads fairly long stretches — typically several hundred bases at a time — but it processes only one fragment per reaction, which makes it slow and costly for whole genomes. Today it remains the trusted choice for confirming small results and checking individual genes, while bulk work has shifted to next-generation methods.