• CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats.
• CRISPR-Cas9 is the most prominent technology that enables to edit parts of the genome by removing, adding or altering sections of the DNA sequence.
• Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) is a gene editing technology, which replicates natural defence mechanism in bacteria to fight virus attacks, using a special protein called Cas9.
• It usually involves the introduction of a new gene, or suppression of an existing gene, through a process described as genetic engineering. CRISPR technology does not involve the introduction of any new gene from the outside.
• The CRISPR-Cas9 system consists of two key molecules that introduce a change mutation into the DNA.
1. Cas9- An enzyme that acts as a pair of ‘molecular scissors’ that can cut the two strands of DNA at a specific location in the genome.
2. Guide RNA (gRNA)- The gRNA is designed to find and bind to a specific sequence in the DNA.
• The Cas9 follows the guide RNA to the same location in the DNA sequence and makes a cut across both strands of the DNA.
• At this stage, the cell recognises that the DNA is damaged and tries to repair it.
• The DNA repair machinery is used to introduce changes to one or more genes in the genome of a cell of interest.
• The technology replicates a natural defence mechanism in some bacteria that uses a similar method to protect itself from virus attacks.

• Advanced research has allowed scientists to develop the highly effective clustered regularly interspaced palindromic repeat (CRISPR) -associated proteins based systems. 

• This system allows for targeted intervention at the genome sequence.

• This tool has opened up various possibilities in plant breeding. Using this tool, agricultural scientists can now edit the genome to insert specific traits in the gene sequence. 

• Depending on the nature of the edit that is carried out, the process is divided into three categories — SDN 1, SDN 2 and SDN 3.

• SDN1 introduces changes in the host genome’s DNA through small insertions/deletions without introduction of foreign genetic material. 

• In the case of SDN 2, the edit involves using a small DNA template to generate specific changes. 
• Both these processes do not involve alien genetic material and the end result is indistinguishable from conventionally bred crop varieties.

•  The SDN3 process involves larger DNA elements or full length genes of foreign origin which makes it similar to genetically modified organisms (GMO) development.

Merits

• Faster and Cheaper- It is faster and cheaper than previous techniques of editing DNA.
• High accuracy- Genetic engineering has made the work more accurate by allowing scientists to have greater control on trait development.
• Viable compared to GMO- CRISPR technology proves viable against the criticisms of Genetically Modified Organisms (GMO).

Applications

• Animal models: CRISPR-Cas9 can be used to create animal models to mimic human diseases and to understand disease development by mutating or silencing genes.
• Genome editing in specific tissues: Researchers have been able to modify the genomes of specific tissues such as liver and brain tissues using hydrodynamic injection and adeno-associated virus (AAV).
• Multiple gene mutations: CRISPR-Cas9 can be used to generate mutants for target genes.
• Treatment of diseases: CRISPR-Cas9 can be applied to cells in vivo or ex vivo. In the in vivo approach, CRISPR-Cas9 is directly transferred to cells in the body using either viral or nonviral methods. In the ex vivo approach, first the cells are removed from the body; then CRISPR is applied to the cells and they are transferred back to the body.
• Health - CRISPR-Cas9 can act as a tool for treating a range of medical conditions that have a genetic component, including cancer, hepatitis B or even high cholesterol. It was shown in mice that it is possible to shut down HIV-1 replication and even eliminate the virus from infected cells. In sickle cell anaemia, a single gene mutation makes the blood sickle-shaped, which can be reversed using gene editing technology. Some scientists are working to create sterile mosquitoes to prevent the vector based transmission of diseases like Malaria.
• Industrial uses: CRISPR was first used for commercial purposes to make bacterial cultures used in cheese and yoghurt production resistant to viral infections.
• RNA editing: Single-stranded RNA (ssRNA) sequences can also be edited by CRISPR-Cas9.
• Military applications: These studies are commonly focused on increasing the tolerance of soldiers against biological or chemical warfare. This technology has the potential to influence human performance optimization.
• Agriculture- CRISPR/Cas9 technology has been used to optimize the shape and size of the crops according to consumer preferences. CRISPR genome-editing technology opens new opportunities to engineer disease resistance traits. Japan has already approved the commercial cultivation of a tomato variety that has been improved using CRISPR-based intervention.

Concerns with CRISPR technology

• Ethical concerns- In 2018, a Chinese researcher’s disclosure of creating a ‘designer baby’ has caused widespread concern in the scientific community.
• Biological concerns- Though the technology is not 100% precise and has the risk of causing mutations, side effects and undesirable changes like antibiotic resistance.
• Genetic drive - Once the manipulated genes get transferred on to next generations, they become part of the environment.
• Gene gap- CRISPR can be very expensive and get limited to those who can afford it.

India in the field of gene editing and CRISPR

• India is at its infancy when it comes to genome editing.
• Research in gene editing is not so abundant but it is growing steadily.
• Although the funding for biology has been steadily growing, a lot of investment is needed in infrastructure.
• India’s draft gene-editing rules allows genome-edited organisms without any “foreign” genes to be subjected to a different regulatory process than the one applied to genetically engineered products.

The technology is not 100% precise and could induce few errors which may be passed to future generations. A specific solution needs to be devised for every disease or disorder that is to be corrected. Ethical dilemmas and potential for misuse of the technology must be considered around its development.