CRISPR (/ˈkrɪspər/) (an acronym for clustered regularly interspaced short palindromic repeats) is a family of DNA sequences found in the genomes of prokaryotic organisms such as bacteria and archaea.[2] Each sequence within an individual prokaryotic cell is derived from a DNA fragment of a bacteriophage that had previously infected the prokaryote or one of its ancestors.[3][4] These sequences are used to detect and destroy DNA from similar bacteriophages during subsequent infections. Hence these sequences play a key role in the antiviral (i.e. anti-phage) defense system of prokaryotes and provide a form of heritable,[3]acquired immunity.[2][5][6][7] CRISPR is found in approximately 50% of sequenced bacterial genomes and nearly 90% of sequenced archaea.[3]
Cas9 (or "CRISPR-associated protein 9") is an enzyme that uses CRISPR sequences as a guide to recognize and open up specific strands of DNA that are complementary to the CRISPR sequence. Cas9 enzymes together with CRISPR sequences form the basis of a technology known as CRISPR-Cas9 that can be used to edit genes within living organisms.[9][10] This editing process has a wide variety of applications including basic biological research, development of biotechnological products, and treatment of diseases.[11][12] The development of the CRISPR-Cas9 genome editing technique was recognized by the Nobel Prize in Chemistry in 2020 awarded to Emmanuelle Charpentier and Jennifer Doudna.[13][14]