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How Did They Sequence DNA?

DNA sequencing can be compared to reading the letters of a very long book. During the Human Genome Project, scientists mainly used a method called Sanger sequencing. This technique works by copying small DNA fragments many times. Special chemicals were added so that each DNA base — A, T, C, or G — produced a signal that could be detected by lasers. Computers then read these signals and reconstructed the DNA sequence (Collins et al., 2003).

Although Sanger sequencing was slow compared to today’s methods, scientists managed to sequence more than 90% of the human genome by 2003. Today, thanks to new technologies, the same task can be completed in just a few hours and at a much lower cost — often under $1,000 per genome (T2T Consortium, 2022).