Hailed as the biggest breakthrough in genetic science this century, CRISPR is shorthand for a molecular toolkit that allows scientists to make precise changes to the genetic code of living organisms. Strictly speaking, the acronym stands for ‘clustered regularly interspaced short palindromic repeats’, a pattern in the DNA of bacteria first noticed by 1987. For years the role of this pattern was mysterious, but in the mid-2000s clues emerged that suggested it was part of the antivirus defence system of bacteria. Studies showed bacteria took sections of a virus’s DNA and built it into their own genome using an enzyme codenamed Cas. The resulting CRISPR sequences then allowed the bacteria to detect an attack and fight back.

But the key breakthrough came in 2012, when teams in the US and Europe led by Jennifer Doudna and Emmanuelle Charpentier showed how the defence system could be turned into a ‘cut and paste’ tool for editing gene sequences. However, another US team beat them to a patent for using the method on human cells, sparking a legal row over priority – and in February 2017, the US patent office ruled against Doudna and Charpentier. Despite this, they remain widely credited as the real pioneers of CRISPR by fellow scientists.

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