GENETICS × TECHNOLOGY

Sanger DNA Sequencing

1977 CE

Phanerozoic · Cenozoic · Quaternary · Holocene · Meghalayan

The chain-termination method of Frederick Sanger, published in 1977, determines the order of the bases, the chemical letters of DNA, by copying a DNA molecule with modified bases that stop the copy wherever they are incorporated.

Sequencing is the reading of the order of the bases along a DNA molecule. The chain-termination method, devised by Frederick Sanger, copies a DNA strand in the presence of modified bases. A modified base stops the copy wherever it is incorporated, so the copies are fragments of every length. The fragments are then sorted by size, so that the sequence can be read directly. Two sequencing methods appeared in 1977, from Cambridge and from Harvard. The chain-termination method prevailed because it was more practical, and geneticists relied on it for thirty years. The first genome read this way was that of the bacteriophage phiX174, a virus that infects bacteria. A genome is the whole DNA of an organism, and this one ran to 5,386 letters.

Why it matters

Every genome cited on this timeline was read with a method derived from chain termination: those of the Neanderthal, the plague bacterium, the ancient wolves and our own. Going from the 5,386 letters of the first genome to three billion letters took twenty-four years. Going from three billion letters to a genome recovered from a finger bone took ten more years.

Dating & uncertainty

The year 1977 is that of the two founding papers, by Sanger, Nicklen and Coulson (1977) and by Maxam and Gilbert (1977). The chain-termination method refines an earlier technique of Sanger's own, published two years before, and is faster and more accurate than that technique.

Earth history as one day

23:59:59.9991933 µs before midnight

if Earth’s 4.54 billion years were compressed into a single day