Gene editing is the precise alteration of an organism's DNA at chosen sites; CRISPR-Cas9, adapted from a bacterial immune system, is the most widely used tool, guiding an enzyme to cut DNA so that genes can be disabled, corrected or changed.
Scientists have been able to change genes since the 1970s, when recombinant DNA techniques allowed genes to be moved between organisms. Early tools for targeted editing, such as zinc finger nucleases and TALENs, existed but were costly and hard to design. In the late 1980s and 1990s, researchers noticed unusual repeating DNA sequences in bacteria, later named clustered regularly interspaced short palindromic repeats (CRISPR). They turned out to be a memory of past viral infections: bacteria store fragments of viral DNA and use them, with Cas proteins, to recognise and cut the virus if it returns.
In 2012, Jennifer Doudna and Emmanuelle Charpentier showed that the CRISPR-Cas9 system could be programmed with a guide RNA to cut any chosen DNA sequence in a test tube. Within months, labs including Feng Zhang's showed it working in human and animal cells. The method was cheap, fast and accurate, and it transformed biology. Doudna and Charpentier received the 2020 Nobel Prize in Chemistry. Later variants such as base editing and prime editing allow single-letter changes without cutting both DNA strands.
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