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CRISPR-Cas9 modifies genomes by using Cas9 guided by a synthetic gRNA to cut DNA at a chosen location.
CRISPR-Cas9 is a genome modification (gene-editing) technique that allows scientists to change the DNA of living organisms. It is adapted from a bacterial immune defense system and works by delivering the Cas9 nuclease together with a synthetic guide RNA (gRNA) into cells. The guide RNA directs Cas9 to a specific DNA sequence, where Cas9 makes a cut (“genetic scissors”), enabling researchers to remove existing genes or insert new ones in vivo. After the DNA break, the cell repairs the cut using either homology-directed repair (HDR) for “knock-in” changes (using an added repair template to insert desired DNA) or end-joining pathways such as non-homologous end joining (NHEJ) and POLQ/TMEJ for “knock-out” mutations. These repair processes can produce targeted disruptions, including random small insertions or deletions that can disable gene function. CRISPR-Cas9 is widely valued for being precise, efficient, and relatively cost-effective, and it has major applications in biotechnology, medicine, agriculture, and research, including potential treatments for inherited diseases and cancers—though germline use in humans is controversial. Variants and alternative CRISPR nucleases have also been developed to improve targeting and reduce off-target effects.
CRISPR-Cas9 modifies genomes by using Cas9 guided by a synthetic gRNA to cut DNA at a chosen location.
Genome changes arise from DNA repair after the cut: HDR enables precise knock-ins, while NHEJ/POLQ/TMEJ often create knock-outs via small disruptive indels.
CRISPR-Cas9 is significant for biotechnology and medicine due to its precision, efficiency, and cost-effectiveness, with major therapeutic and research applications and ongoing ethical and safety considerations.
A gene-editing system that uses the Cas9 nuclease guided by RNA to cut DNA at a targeted sequence so the genome can be modified.
A synthetic RNA that directs Cas9 to the complementary DNA target sequence in the genome.
An enzyme that creates a double-stranded DNA break at the site specified by the guide RNA.
A DNA repair pathway that uses a provided template to make precise “knock-in” edits after Cas9 cutting.
A DNA repair pathway that joins broken DNA ends without a template, often producing random insertions or deletions that disrupt genes.
An end-joining repair mechanism that can also generate insertions/deletions at the break site, contributing to gene knock-outs.
A targeted insertion of new DNA into the genome, typically achieved using HDR with a repair template.
A gene-disrupting change, often caused by indels from end-joining repair after Cas9-induced double-strand breaks.
Unintended DNA edits at sites other than the intended target, which newer CRISPR variants aim to reduce.
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