CRISPR started out as a defence system in bacteria, which store snippets of virus DNA and cut up any virus that matches them. In 2012 Jennifer Doudna and Emmanuelle Charpentier showed it could be programmed to cut DNA at almost any chosen spot, which made editing genes far easier.
The name stands for ‘clustered regularly interspaced short palindromic repeats’: short DNA sequences repeated at regular intervals, with the virus snippets stored between them. Japanese researchers first noticed the pattern in 1987, and the Spanish microbiologist Francisco Mojica later worked out that it serves as an immune memory. The editing tool pairs a cutting protein, Cas9, with a short guide made of RNA, DNA's chemical cousin, that leads it to the matching DNA. When the cell repairs the cut, a gene can be switched off, or scientists can slip in a corrected version. Doudna and Charpentier won the 2020 Nobel Prize in Chemistry. In November 2023 the UK became the first country to approve a CRISPR treatment: Casgevy, for the inherited blood disorders sickle cell disease and beta thalassaemia. The method also raises ethical questions: in 2018 the Chinese scientist He Jiankui edited human embryos and was later jailed.





