ĬRISPR-Cas9 genome editing techniques have many potential applications, including in medicine and agriculture. Newly engineered variants of the Cas9 nuclease have been developed that significantly reduce off-target activity. The ease with which researchers can insert Cas9 and template RNA in order to silence or cause point mutations at specific loci has proved invaluable to the quick and efficient mapping of genomic models and biological processes associated with various genes in a variety of eukaryotes. Cas9 derived from the bacterial species Streptococcus pyogenes has facilitated targeted genomic modification in eukaryotic cells by allowing for a reliable method of creating a targeted break at a specific location as designated by the crRNA and tracrRNA guide strands. With the discovery of CRISPR and specifically the Cas9 nuclease molecule, efficient and highly selective editing is now a reality. While genome editing in eukaryotic cells has been possible using various methods since the 1980s, the methods employed had proved to be inefficient and impractical to implement on a large scale. Genomic editing leads to irreversible changes to the genome. Because of this, the precision of genome editing is a great concern. Therefore, genomic engineering by CRISPR-Cas9 gives researchers the ability to generate targeted random gene disruption. NHEJ can often result in random deletions or insertions at the repair site, which may disrupt or alter gene functionality. Knock-out mutations caused by CRISPR-Cas9 result in the repair of the double-stranded break by means of non-homologous end joining (NHEJ). This method relies on the periodic and isolated occurrence of DNA damage at the target site in order for the repair to commence. HDR employs the use of similar DNA sequences to drive the repair of the break via the incorporation of exogenous DNA to function as the repair template. This allows for the introduction of targeted DNA damage and repair. Knock-in mutations, facilitated via homology directed repair (HDR), is the traditional pathway of targeted genomic editing approaches. Working like genetic scissors, the Cas9 nuclease opens both strands of the targeted sequence of DNA to introduce the modification by one of two methods. The third researcher group that shared the Kavli Prize for the same discovery, led by Virginijus Šikšnys, was not awarded the Nobel prize. The development of the technique earned Jennifer Doudna and Emmanuelle Charpentier the Nobel Prize in Chemistry in 2020. However, its use in human germline genetic modification is highly controversial. It also has possibilities in the treatment of inherited genetic diseases as well as diseases arising from somatic mutations such as cancer.

It can be used in the creation of new medicines, agricultural products, and genetically modified organisms, or as a means of controlling pathogens and pests. The technique is considered highly significant in biotechnology and medicine as it enables editing genomes in vivo very precisely, cheaply, and easily. By delivering the Cas9 nuclease complexed with a synthetic guide RNA (gRNA) into a cell, the cell's genome can be cut at a desired location, allowing existing genes to be removed and/or new ones added in vivo. It is based on a simplified version of the bacterial CRISPR- Cas9 antiviral defense system. CRISPR gene editing (pronounced / ˈ k r i s p ə r/ 'crisper') is a genetic engineering technique in molecular biology by which the genomes of living organisms may be modified.

Gene expression c artoon