Biology · Biotechnology and Its Applications · NEET
Gene therapy is a collection of methods that corrects a gene defect already diagnosed in a child or embryo. A normal (functional) gene is inserted into the person's cells and tissues so it takes over the job of the faulty, non-functional gene. Memory hook: "Bad gene inside you, put a good gene into you." The first-ever clinical gene therapy was done in 1990 on a 4-year-old girl with ADA deficiency.
Gene therapy flow: a faulty gene is diagnosed, then a normal gene is carried by a retroviral vector into the patient's cells, where it works in place of the non-functional gene. It compensates for the defect rather than removing it.
Your doubts, answered
Is gene therapy the same as genetic engineering or GMO work?
No. Genetic engineering is the general lab technique of cutting and joining DNA. Gene therapy is one medical application of it: correcting a gene defect that has already been diagnosed in a person, by inserting a normal gene into that person's cells and tissues to treat a disease (especially a hereditary disease). NEET tests gene therapy as an 'application in medicine', so link it to treating an inherited disorder, not to making crops.
Does gene therapy fix the old faulty gene or give a new working one?
In the NCERT sense, a normal gene is delivered to take over the function of and compensate for the non-functional gene. So the healthy gene does the work; the defect is corrected either by replacing a defective allele with a functional one, or by gene targeting (which involves gene amplification). Both endings appear in matching-type PYQs, so remember the exact NCERT phrase: 'allows correction of a gene defect'.
Is gene therapy a permanent cure?
Not necessarily. In the ADA example, corrected lymphocytes are not immortal, so the patient needs periodic infusion of the genetically engineered lymphocytes. A permanent cure would need the gene put into cells at early embryonic stages (for example, a gene from marrow cells producing ADA). NEET 2022 tested exactly this 'not immortal, so repeat infusion' point.
Is gene therapy done before or after the defect is diagnosed?
After. NCERT defines it as correcting a gene defect 'that has been diagnosed in a child/embryo'. So diagnosis comes first, then the corrective gene is delivered. This is why molecular diagnosis and gene therapy are studied close together in the chapter.
⚠️ The NEET trap ✗ Gene therapy destroys or removes the faulty gene from the body. ✓ A normal gene is inserted to take over the function of and compensate for the non-functional gene. NCERT never says the bad gene is removed; the healthy gene simply does the work. 🧠 Compensate, not delete: gene therapy adds a working gene, it does not cut out the old one.
Real NEET questions
NEET 2021
When gene targeting involving gene amplification is attempted in an individual's tissue to treat disease, it is known as:
A · Molecular diagnosis
B · Safety testing
C · Biopiracy
D · Gene therapy ✓
Solution: Gene therapy inserts genes into a person's cells and tissues to treat a hereditary disease. It corrects a gene defect either by replacing a defective allele with a functional one or by gene targeting, which involves gene amplification - exactly the process in the stem.
NEET 2016 (Phase 2)
Which kind of therapy was given in 1990 to a four-year-old girl with adenosine deaminase (ADA) deficiency?
A · Gene therapy ✓
B · Chemotherapy
C · Immunotherapy
D · Radiation therapy
Solution: The first clinical gene therapy was given in 1990 to a 4-year-old girl with ADA deficiency. A functional ADA cDNA (via a retroviral vector) is introduced into her lymphocytes to compensate for the deleted gene.
NEET 2023 (Phase 2)
Match List I with List II: (A) Gene therapy (B) RNA interference (C) ELISA (D) Gel Electrophoresis with (I) Separation of DNA fragments (II) Diagnostic test for AIDS (III) Cellular defence (IV) Allows correction of a gene defect.
A · (A)-IV, (B)-III, (C)-II, (D)-I ✓
B · (A)-IV, (B)-III, (C)-I, (D)-II
C · (A)-IV, (B)-I, (C)-II, (D)-III
D · (A)-IV, (B)-II, (C)-III, (D)-I
Solution: Gene therapy allows correction of a gene defect (IV); RNAi is cellular defence (III); ELISA detects HIV, i.e. a diagnostic test for AIDS (II); gel electrophoresis separates DNA fragments (I). So (A)-IV, (B)-III, (C)-II, (D)-I.
Solved Biotechnology and Its Applications NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Gene therapy is a collection of methods that allows correction of a gene defect diagnosed in a child or embryo, by inserting a normal gene into the person's cells and tissues to treat the disease.
What is the standard NEET example of gene therapy?
ADA (adenosine deaminase) deficiency. The first clinical gene therapy was given in 1990 to a 4-year-old girl with this disorder, using a functional ADA cDNA delivered by a retroviral vector into her lymphocytes.
Which vector is used to carry the healthy gene in gene therapy?
A virus, usually a retrovirus. Viruses that insert their genetic material into host cells during their replication cycle are used as vectors to carry healthy genes into human cells (for ADA therapy, into lymphocytes).
Why is one gene therapy treatment not always enough?
The corrected cells (lymphocytes) are not immortal, so they die over time. The patient then needs periodic infusion of fresh genetically engineered lymphocytes. A permanent cure would require introducing the gene at early embryonic stages.
