What is CRISPR?
[[File:SimpleCRISPR.jpg|thumb|Diagram of a CRISPR [[locus]]. There are three main parts. <br/>1. ''cas'' genes, <br/>2. a leader sequence, and <br/>3. A repeat-spacer array. <br/>The arrangement of the three components is not always as shown]] [[File:4QYZ.png|thumb|CRISPR Cascade protein (cyan) bound to CRISPR RNA (green) and phage DNA (red)]] [[File:GRNA-Cas9.svg|thumb|CRISPR/Cas9]] '''CRISPR''' is a term in [[DNA]] research. It stands for ''clustered regularly-interspaced short palindromic repeats''. These are part of the [[genetic code]] in [[prokaryote]]s: most [[bacteria]] and [[archaea]] have it. It is their defence against attack by [[viruses]].<ref>Grissa I; Vergnaud G. & Pourcel C. 2007. The CRISPRdb database and tools to display CRISPRs and to generate dictionaries of spacers and repeats. ''BMC Bioinformatics'' '''8''': 172. [http://bmcbioinformatics.biomedcentral.com/articles/10.1186/1471-2105-8-172]</ref> Its structure and function was discovered in the 21st century.<ref>Gesner E.M; Schellenberg M.J; Garside E.L; George M.M. & Macmillan A.M. 2011. Recognition and maturation of effector RNAs in a CRISPR interference pathway. ''Nature Structural & Molecular Biology''. '''18''' (6): 688–692.</ref><ref>See [[Nobel Prize in Chemistry]] to [[Emmanuelle Charpentier]] and [[Jennifer Doudna]], 2020.</ref><ref>Wiedenheft B; Sternberg S.H; Doudna J.A. 2012. RNA-guided genetic silencing systems in bacteria and archaea. ''Nature''. '''482''' (7385): 331–338.[https://pubmed.ncbi.nlm.nih.gov/22337052/]</ref> CRISPR has a lot of short repeated sequences. These sequences are part of an [[adaptive immune system]] for prokaryotes. It allows them to remember and counter the [[bacteriophage]]s which prey on them. They work as a kind of [[acquired immune system|acquired immunity]] for bacteria.<ref>Lecture by [[Jennifer Doudna]] [https://www.youtube.com/watch?v=47pkFey3CZ0]</ref><ref>Mojica F.J.M. et al 2000. Biological significance of regularly spaced repeats in the genomes of Archaea, Bacteria and mitochondria. ''Mole