TECHNOLOGY × GENETICS

The Molecular Photocopier

1985 CE

History · Contemporary · Holocene · Meghalayan

The polymerase chain reaction does one thing: from a trace of DNA it makes millions of copies of a chosen segment, cycling the temperature and letting a polymerase rebuild what heat has pulled apart. Kary Mullis and colleagues applied it at Cetus in 1985, and it became practical in 1988, when a polymerase from a heat-loving bacterium proved able to survive the boiling step. Amplification reached a factor of more than ten million, enough to find a single target molecule in a sample of a hundred thousand cells.

Why it matters

PCR turned scarcity of DNA from a wall into an inconvenience, and half of modern biology walks through the opening: diagnostics, forensics from a fingerprint's worth of cells, ancient DNA read out of fossil bones, the tests that counted a pandemic. It also makes the case for curiosity-driven research better than any argument could, since the enzyme that made it work came from a bacterium in a Yellowstone hot spring, studied long before anyone could say why it would matter.

Dating & uncertainty

Kary Mullis conceived the reaction at Cetus, where it was first applied experimentally in 1985; a theoretical outline had been published in 1971 and gone nowhere. The practical turn came in 1988 with a heat-proof polymerase from Thermus aquaticus, a hot-spring bacterium: it survives the boiling step, and it let the cycles be run by machine, unattended.

Sources

1. Saiki et al. (1988), Science · Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerasedoi:10.1126/science.2448875
2. Lorenz (2012), Journal of Visualized Experiments · Polymerase chain reaction: basic protocol plus troubleshooting and optimization strategiesdoi:10.3791/3998
3. Nikiforov (2001), Springer · Polymerase chain reactiondoi:10.1007/978-1-59259-190-9_11

Our species’ history as one day

23:59:4811.2 s before midnight

if the 315,000 years of Homo sapiens were compressed into a single day