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Genomics, gene editing and cell therapy
Start here explains gene editing, from CRISPR to base and prime editing. The theme then follows genome projects, gene and cell therapy, stem cells and their regulation, epigenetics and the microbiome. Prelims has asked about the GenomeIndia Project and what somatic cell nuclear transfer is used for.
UPSC has asked
- Prelims 2026: the GenomeIndia Project
- Prelims 2017: what somatic cell nuclear transfer is used for
All 5 subjects shown; the 1 that changed from 1 to 15 July 2026 are marked.Show only these
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Gene editing: CRISPR, base editing and prime editing
Copy link to Gene editing: CRISPR, base editing and prime editingPrelims and MainsAdded 20 September
Gene editing changes DNA at a chosen place. CRISPR Cas9, adapted from a bacterial defence against viruses and awarded the 2020 Nobel Prize in Chemistry, has two parts: a guide RNA that matches the target sequence, and the Cas9 enzyme that cuts both strands of the DNA there. The cell then repairs the cut, and the repair is the edit: quick repair usually disables the gene, and with a template the cell copies a new sequence in. Base editing avoids the double strand cut: a disabled Cas9 carries an enzyme that chemically changes one letter into another, so a single point mutation can be corrected. Prime editing goes further, carrying a template and a reverse transcriptase that writes a new sequence directly. Delivery is the practical problem: the machinery must reach the right cells, by a harmless virus, a lipid particle, or by editing cells outside the body.
How a CRISPR edit happens
1 Target
A guide RNA is designed to match the DNA sequence to be changed.
2 Cut
Cas9 binds the guide, finds the match and cuts both strands.
Without the cut: Base editing changes one letter chemically; prime editing writes a new sequence with a reverse transcriptase; both avoid the double strand break.
3 Repair
The cell repairs the break: quick repair disables the gene; repair from a supplied template inserts a new sequence.
4 Deliver
The machinery reaches the cells by virus, lipid particle or editing outside the body.
5 Check
Sequencing confirms the edit and looks for off target cuts.
- Medicine: the first approved CRISPR therapy, for sickle cell disease and beta thalassaemia, edits a patient's own blood stem cells outside the body to switch fetal haemoglobin back on; India, with a large sickle cell burden in tribal districts, has its own therapy in trials.
- Crops: a plant edited without foreign DNA (SDN 1, a disabled gene; SDN 2, a small templated change) is exempt in India from the genetically modified approval process since 2022, while SDN 3, with inserted foreign DNA, is regulated as genetically modified; the first two genome edited rice varieties were released in 2025.
- The limits: off target cuts elsewhere in the genome, mosaicism when not every cell is edited, and immune reactions to Cas9; base and prime editing reduce the first.
- Germline editing, changing embryos so the edit is inherited, is banned or unapproved almost everywhere, and the 2018 case of edited babies in China is the reference point for why.
- India's framework: the Indian Council of Medical Research guidelines on biomedical research, the Department of Biotechnology guidelines for genome edited plants (2022) and organisms, and the Genetic Engineering Appraisal Committee (GEAC) for anything that counts as genetically modified; GenomeIndia, which sequenced 10,000 Indian genomes, is the reference genome the edits will be measured against.
Mains: Gene editing separates two questions that genetic modification mixed together, whether foreign DNA is added and whether a gene is changed, and India's 2022 rules answered the first, which is why edited crops can reach farmers years faster than genetically modified ones.
UPSC has asked
- Prelims 2019: what the Cas9 protein does
- Prelims 2018: the field CRISPR Cas9 belongs to
See also: Base editing · Epigenetics · Proven stem cell therapies · Regulation of stem cell therapy · GM crops in India: what is approved, who approves
Epigenetics
Copy link to EpigeneticsPrelims and Mains
A gene is a stretch of DNA whose sequence of bases spells out one protein, and Mendel's rules have each of its two copies passed on unchanged and independently. A map of the chemical marks carried on the DNA of two mouse strains has now turned up more than 500 instances of inheritance those rules do not predict.
- A gene is felt only when it is read: transcription copies it into messenger ribonucleic acid (mRNA), and translation builds the protein from that copy.
- The marks mapped were DNA methylation, read across the two strains by nanopore sequencing.
- In some regions the methylation depended on the mouse's sex.
- Marks could copy from one gene copy to the other.
- Similar mechanisms may explain human conditions that resist standard genetic analysis.
What changed
Proven stem cell therapies
Copy link to Proven stem cell therapiesPrelims and Mains
Every proven use replaces a tissue with the same tissue, and each took decades of trials to reach the clinic. The list is short, and a good deal shorter than what clinics advertise.
- Haematopoietic stem cell transplantation, the bone marrow transplant, treats leukaemia, lymphoma, thalassaemia and aplastic anaemia.
- Limbal stem cells from the eye restore a cornea scarred by chemical burns.
- Cultured skin cells are grafted onto severe burns.
- Other conditions, neurological and degenerative disease among them, remain investigational, for an approved clinical trial only.
- No whole organ has yet been grown from stem cells for human transplant.
What changed
Regulation of stem cell therapy
Copy link to Regulation of stem cell therapyPrelims and Mains
Research and the products sold as treatment fall to different regulators. The newest guidelines are a layer added on top of that division rather than a replacement for it.
- The National Stem Cell Research Regulation Committee oversees research using minimally manipulated stem cells.
- The Central Drugs Standard Control Organisation (CDSCO) regulates stem cell products as drugs, under the New Drugs and Clinical Trials Rules, 2019.
- The Health Ministry's Centre for Evidence Based Guidelines issued guidelines on stem cell therapy and regenerative medicine for 2025 to 2026.
- They join the National Guidelines for Stem Cell Research 2017, the gene therapy guidelines 2019, the haematopoietic cell transplantation guidelines 2021 and the cord blood banking guidelines 2023.
- India's first in human gene therapy trial was run by the Centre for Stem Cell Research with Christian Medical College, Vellore.
What changed
Base editing
Copy link to Base editingPrelims and Mains
Base editing, developed in 2016, converts one DNA letter into another without cutting both strands, unlike CRISPR-Cas9, so it should cause fewer unintended changes. Delivery to the brain needs large doses of adeno associated viruses, which can provoke a severe immune reaction.
What changed
26 Jul 2026New subject
- A six year old girl in China with a rare disorder caused by the CHD3 gene died after what is thought to be the first base editing therapy directed at the brain. It ran as a hospital trial that needed no review by the national drug regulator, and her parents funded much of it.
Mains: the gap was between the rules and their enforcement, as with He Jiankui's embryo editing in 2018.
UPSC has asked
- Prelims 2020: germline editing and human induced pluripotent stem cells in a pig embryo
Gene drives
Copy link to Gene drivesMains
A gene drive is engineered DNA that passes to far more than half of an organism's offspring and so spreads through a wild population, proposed for collapsing mosquito populations and opposed for effects that cannot be reversed.
What changed
14 Jul 2026New subjectalso in news
- A gene drive is engineered DNA that passes to far more than half the offspring and so spreads through a wild population. The proposed use is to collapse mosquito populations, and the concerns are resistance and effects that cannot be reversed.