Gene Editing (CRISPR) and Gene Therapy
Science & Technology › Biotechnology – Principles and Techniques · Topic 10.10
Gene editing is the precise change of DNA at a chosen site in a living cell, and the best known tool is CRISPR-Cas9, in which a guide RNA leads the Cas9 enzyme to a matching DNA sequence where it makes a cut that the cell then repairs, allowing a gene to be disabled, corrected or inserted. Emmanuelle Charpentier and Jennifer Doudna described the system in 2012 and received the Nobel Prize in Chemistry in 2020. Gene therapy is the treatment of disease by adding, replacing or editing genes in a patient. In late 2023 the first CRISPR therapy, Casgevy, was approved in the United Kingdom and the United States for sickle cell disease and beta thalassaemia.
5 min read · UPSC Prelims · Science & Technology · Biotechnology – Principles and Techniques
At a Glance
- Tool CRISPR-Cas9
- Nobel Charpentier and Doudna, 2020
- First approved CRISPR drug Casgevy, late 2023
- Therapy types Somatic and germline
- India Sickle cell therapy work
- Exam link UPSC Prelims, Science & Technology: Biotechnology – Principles and Techniques
Where Does It Fit?
This topic follows antibody-antigen methods. It moves from detecting biological molecules to changing them, which is the most powerful and most debated technique of the macro. Previous topic: Antibody-Antigen Interaction and Detection Methods. Next topic: Stem Cell Biotechnology and Engineering.
How Does CRISPR Gene Editing Work?
| Part | Role |
|---|---|
| CRISPR | Clustered Regularly Interspaced Short Palindromic Repeats, a bacterial defence system against viruses |
| Guide RNA | A short RNA that matches the target DNA and leads Cas9 to it |
| Cas9 enzyme | A molecular scissors that cuts both strands of DNA near the target |
| Repair by non-homologous end joining | The cell joins the ends quickly and often adds errors, which switches a gene off |
| Repair by homology | If a template is supplied, the cell copies it to fix or insert a sequence |
| Base editing and prime editing | Newer tools that change single bases without cutting both strands, which lowers errors |
| Other tools | Zinc finger nucleases and TALENs are older proteins that cut DNA at chosen sites |
What Are the Types and Uses of Gene Therapy?
- Somatic gene therapy: changes body cells of a patient and is not passed to children
- Germline gene therapy: changes eggs, sperm or embryos, so the change is inherited. It is banned or tightly restricted in most countries
- In vivo and ex vivo: in vivo therapy delivers genes inside the body, while ex vivo therapy edits cells outside and returns them
- Viral vectors: adeno associated viruses and lentiviruses carry genes into cells
- Sickle cell disease: Casgevy edits blood stem cells to raise fetal haemoglobin
- Inherited blindness: Luxturna, approved in 2017 in the United States, replaces a faulty gene in the eye
- Cancer: CAR-T cell therapy changes the patients own T cells to attack tumour cells
- Agriculture: edited crops with disease resistance, longer shelf life or better nutrition
What Else Should You Remember?
- Nobel Prize 2020: Emmanuelle Charpentier and Jennifer Doudna received the Chemistry prize. Feng Zhang and George Church also developed CRISPR for human cells
- Controversy of 2018: Chinese scientist He Jiankui announced birth of edited babies, which caused worldwide condemnation and a prison sentence for him
- Off target effects: edits at wrong sites can cause harm, so accuracy is checked
- Delivery problem: getting the editor to the right cells in the body is hard
- Cost: one time gene therapies cost hundreds of thousands to millions of dollars, which raises equity concerns
- India: the Indian Council of Medical Research has ethical guidelines for gene therapy, and the Department of Biotechnology and others have worked on sickle cell therapy. In 2025 an indigenous CRISPR based therapy for sickle cell disease was announced. Check the current status before quoting
- Genome edited plants: India released two genome edited rice varieties in May 2025, using SDN-1 and SDN-2 methods that carry no foreign DNA
- Link: the editing guide molecules are described in Types of RNA and Their Technological Applications
- Gene silencing: RNA interference switches genes off without changing the DNA
- Ethics: enhancement, designer babies and unequal access are the main concerns, as in Designer Babies/Three-Parent Babies
- Prime editing: a newer tool that can write small insertions and deletions using a modified Cas9 and a template carried in the guide, without a double strand cut
- Spinal muscular atrophy: gene therapy with a virus that carries a working gene has been approved for this condition in infants
Why Does It Matter for the Exam?
- Components: Cas9, guide RNA and what each does
- Nobel: 2020 Chemistry prize winners
- Therapy types: somatic versus germline
- Current affairs link: new approvals and Indian sickle cell therapy
- Common errors: saying that CRISPR cuts RNA with Cas9, or that germline editing is legal in India
As an analytical point, gene therapy offers cures for single gene diseases but at a very high price. India, with a heavy sickle cell and thalassaemia burden, has a strong case to develop low cost indigenous therapies under clear ethical rules.
Why Is This Topic Important?
- Mechanism Guide RNA and Cas9
- Medicine Cures for blood diseases
- Ethics Germline limits
What Came Next?
The next topic covers stem cell biotechnology and engineering. Next topic: Stem Cell Biotechnology and Engineering.
Key People and Terms
- CRISPR Bacterial DNA defence repeats
- Cas9 DNA cutting enzyme
- Guide RNA Target finder
- Base editing Single base change tool
- Somatic Body cell, not inherited
- Germline Inherited cells
Exam Corner
Points to Remember
- CRISPR Nobel: 2020, Charpentier and Doudna.
- First CRISPR drug: Casgevy, 2023.
- Cas9 cuts DNA.
- Germline editing is restricted.
- Genome edited rice varieties in India: 2025.
Do Not Confuse With
- Gene editing and gene therapy Tool versus treatment
- Somatic and germline Not inherited versus inherited
- CRISPR and RNA interference Changes DNA versus silences RNA
Memory Hook
Guide RNA finds the spot, Cas9 cuts the strand, the cell mends the gap.
Mains Angle
Questions ask about how CRISPR works and about ethics. These points help.
- Promise Cures and crops
- Risks Off target and ethics
- India Rules and access
A Question You May Face
An original practice question, not a past paper question.
“Discuss the potential and the ethical concerns of CRISPR gene editing and gene therapy and the regulatory approach that India should take.”
How to Answer
- Mechanism Guide RNA, Cas9.
- Promise Blood diseases, crops.
- Concerns Germline, cost.
- Way Rules and local therapy.
GS Relevance
Frequently Asked Questions
What is CRISPR-Cas9?
CRISPR-Cas9 is a gene editing tool adapted from a bacterial defence system. A guide RNA matches a chosen DNA sequence and leads the Cas9 enzyme to it, where the enzyme cuts both strands. The cell then repairs the cut, allowing a gene to be switched off, corrected or replaced.
Who won the Nobel Prize for CRISPR?
Emmanuelle Charpentier and Jennifer Doudna won the Nobel Prize in Chemistry in 2020 for developing a method of genome editing based on CRISPR-Cas9. They showed in 2012 that the bacterial system could be programmed with a guide RNA to cut any chosen DNA sequence.
What is the difference between somatic and germline gene therapy?
Somatic gene therapy changes the genes in body cells of a patient, and the change is not passed to children. Germline gene therapy changes eggs, sperm or embryos, so the change is inherited by later generations. Germline editing is banned or tightly restricted in most countries because of ethical risks.
What is Casgevy?
Casgevy is the first approved CRISPR based therapy. Approved in the United Kingdom and the United States in late 2023, it treats sickle cell disease and transfusion dependent beta thalassaemia by editing a patient's blood stem cells to raise fetal haemoglobin production.
What are the risks of gene editing?
The main risks are off target edits at wrong places in the genome, unwanted changes in cells, difficulty of delivery to the right tissue, very high cost, and ethical concerns about editing human embryos and enhancing traits. Careful testing, regulation and long term follow up are needed.
PYQ Practice — Statement Analysis
1 The Nobel Prize in Chemistry 2020 was awarded for CRISPR gene editing.
To Charpentier and Doudna.
2 Cas9 is an enzyme that cuts DNA.
Guided by RNA.
3 Germline gene therapy changes are not passed to offspring.
They are inherited.
4 Casgevy is a therapy for sickle cell disease.
First approved CRISPR therapy.
Past Mains Questions on This Topic
This topic comes under Biotechnology – Principles and Techniques. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
Related Topics
Browse the full Science & Technology index