Q.When an abnormal gene is replaced by normal gene, what do you call it?
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Gene Therapy
Gene therapy corrects a hereditary disease by delivering a normal, functional copy of a gene, via a vector, into the cells of a patient carrying a mutant allele, so that the expressed normal gene product restores a normal phenotype; it has mainly targeted single-gene disorders like cystic fibrosis and haemophilia, for which no other effective treatment exists. Two strategies exist — gene augmentation therapy (adding a working gene copy) and gene inhibition therapy (silencing a harmful dominant gene with an antisense gene) — and two levels of application: somatic cell gene therapy (targeting non-reproductive cells like bone marrow, blood or skin; corrects the patient but is not inherited) and germline gene therapy (targeting eggs or sperm; heritable, and far more ethically contentious). The landmark case is ADA-deficiency SCID, first treated clinically by French Anderson in 1990 in a four-year-old girl: lymphocytes are drawn from the patient's blood, infected in culture with a disabled retrovirus carrying a working ADA gene, and reinfused; because these engineered cells are not immortal the patient needs periodic repeat infusions, and only introducing the corrected g …
Correcting a genetic disease by delivering a working copy of a defective gene is a specific technique, distinct from gene mutation, gene cloning, or gene ligation. …
Gene therapy is the technique of correcting a genetic defect by delivering a normal, functional gene to replace or supplement the patient's abnormal (mutant) gene.
Gene therapy is a collection of methods that allow correction of a gene defect diagnosed in a child/embryo. Genetic material (a normal, healthy copy of the gene) is inserted into an individual's cells and tissues to treat a disease caused by a defective (mutant) gene. The classic example taught in NCERT is the treatment of Adenosine Deaminase (ADA) deficiency, caused by the deletion of the gene for ADA, an enzyme crucial for immune function:
- Lymphocytes from the patient's blood are grown in culture outside the body.
- A functional ADA cDNA is introduced into these lymphocytes using a retroviral vector.
- These genetically corrected cells are returned to the patient. …
Showing the 12 most recent of 15 on this concept.
- CBSE 2026Set A1 markMCQQ.Gene therapy was first used to remove the deficiency of which of the following enzymes?(a) DNA polymerase(b) Uracil DNA glycosylase(c) Adenosine deaminase(d) Beta galactosidase
›Reveal solutionSolution
The first gene therapy was for adenosine deaminase (ADA) deficiency; the correct option is (c).
The first clinical gene therapy was given in 1990 to a four-year-old girl suffering from adenosine deaminase (ADA) deficiency, which causes a severe immunodeficiency (SCID). ADA deficiency is caused by the deletion or defect of the gene coding for the enzyme adenosine deaminase. In the therapy, lymphocytes from the patient's blood were grown in culture, a functional ADA gene (using a …
- CBSE 2026Set ANNUAL1 markQ.Fill in the blank: The first clinical gene therapy was given in 1990 to a four year girl to cure deficiency of ______.
›Reveal solutionSolution
The first approved human gene therapy (1990) treated a girl born with ADA deficiency, a genetic immune disorder.
Adenosine deaminase (ADA) deficiency is caused by deletion of the gene encoding ADA, which is needed for normal immune function; in some cases it can be corrected by bone marrow transplant or enzyme replacement, but the underlying disease is not fully cured this way. In 1990, the first clinical gene therapy was given to a four-ye …
- CBSE 2026Set ANNUAL1 markQ.ADA is a genetic disorder due to the absence of an enzyme. Name the enzyme that is absent.
›Reveal solutionSolution
ADA deficiency is named directly for the missing enzyme, adenosine deaminase, whose absence severely compromises the immune system.
Adenosine Deaminase (ADA) deficiency is a genetic disorder caused by the deletion/absence of the gene coding for the enzyme adenosine deaminase. This enzyme is essential for normal functioning of lymphocytes; its absence leads to toxic accumulation of its substrate, deoxyadenosine, which is particularly harmful to developing lymphocytes, c …
- CBSE 2025Set A1 markQ.Write True / False: ADA deficiency can be cured by Lymphocytes.
›Reveal solutionSolution
The statement is True: ADA deficiency is treated by gene therapy performed on the patient's lymphocytes.
Adenosine Deaminase (ADA) deficiency is a genetic (SCID-causing) disorder in which the enzyme ADA, essential for immune function, is missing due to a defective gene. As the first approved gene-therapy procedure (1990), lymphocytes are extracted from the patient's blood, grown in culture outside the body, and a functional copy of the ADA cDNA is introduced into these lymphocytes using a retroviral vector. These genetically corrected lymphocytes are then returned to the patient, allowing them to pr …
- CBSE 2025Set ANNUAL1 markMCQQ.The first clinical gene therapy was given for treating(a) Diabetes mellitus(b) Chicken pox(c) Rheumatoid arthritis(d) ADA deficiency
›Reveal solutionSolution
The first clinical application of gene therapy in humans, in 1990, was used to treat adenosine deaminase (ADA) deficiency, a genetic immune disorder.
ADA deficiency arises from a defective/missing gene for the enzyme adenosine deaminase, which is essential for the normal functioning of lymphocytes (immune cells); its loss leads to severe combined immunodeficiency (SCID). In the first approved human gene therapy trial, lymphocytes were taken from the patient's blood, cultured, and a functional copy of the ADA gene was introduced into them using a retroviral vector; these genetically corrected cells were then reintroduced into the …
- CBSE 2025Set ANNUAL1 markMCQQ.The first clinical application of gene therapy over a 4 year old girl was for(a) Adenosine deaminase deficiency(b) Adenosine deficiency(c) Growth deficiency(d) Adenine deficiency
›Reveal solutionSolution
The first-ever human gene therapy trial (1990) treated a 4-year-old girl for adenosine deaminase (ADA) deficiency, an inherited immunodeficiency.
Gene therapy is a biotechnological approach in which a normal, functional gene is introduced into an individual to compensate for a defective/absent gene, aiming to correct a genetic defect. The first clinical application of gene therapy was performed in 1990, on a 4-year-old girl who suffered from Adenosine Deaminase (ADA) deficiency, a rare inherited disorder in which the enzyme adenosine deaminase, essential for the proper functioning of the immune system, is missing (due to the deletion of the ADA gene). In severe cases, this condition can be treated by bone marrow transplantation or enzyme replacement therapy, but as a more permanent solution, gene therapy involves isolating and reintroducing norma …
- CBSE 2025Set ANNUAL1 markMCQQ.A boy is born with a hereditary disease, what corrective method will you suggest ?(i) Gene cloning(ii) Nuclear transfer(iii) Organism cloning(iv) Gene therapy
›Reveal solutionSolution
Gene therapy is the corrective method for hereditary genetic disorders — it works by delivering a normal, functional copy of the defective gene into the patient's cells.
Gene therapy is a collection of methods that allows correction of a gene defect diagnosed in a child or embryo. In this approach, genes are inserted into a person's cells and tissues to treat a disease that has resulted from a faulty/mutated gene. A normal, healthy copy of the gene is introduced into the patient's cells (often using a vector, e.g. a modified retrovirus) to compensate for the non-functional gene, and this corrected cell population is expected to produce the normal protein needed. The classic example is the treatment of Adenosine Deaminase (ADA) deficien …
- CBSE 2024Set D1 markQ.Fill in the blank: ______ is caused by mutation in the gene related to the adenosine deaminase enzyme.
›Reveal solutionSolution
Severe Combined Immunodeficiency (SCID), specifically ADA deficiency, results from a mutated/defective gene for the enzyme adenosine deaminase.
Adenosine deaminase (ADA) is an enzyme essential for the normal functioning of lymphocytes (immune cells). In some children, this enzyme is deficient due to the deletion of the gene that codes for it, and in others the defect is in the ADA gene itself (a genetic — often autosomal recessive — mutation).
This deficiency leads to Severe Combined Immunodeficiency (SCID), in which the affected individual has little to no functioning immune system and is highly vulnerable to infections.
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- CBSE 2023Set 57/1/11 markMCQQ.Assertion (A) : A patient of ADA deficiency undergoing treatment for gene therapy requires periodic infusion of genetically engineered lymphocytes. Reason (R) : Lymphocytes are immortal.(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) is false, but Reason (R) is true.
›Reveal solutionSolution
The assertion is true — ADA deficiency patients do need periodic infusions of engineered lymphocytes — but the reason given is false; lymphocytes are not immortal, which is exactly why the infusions must be repeated.
Let’s begin with the context. Severe Combined Immunodeficiency (SCID) caused by adenosine deaminase (ADA) deficiency was one of the earliest targets for gene therapy. The NCERT textbook describes the first successful clinical trial: lymphocytes were taken from the patient, the normal ADA gene was inserted into them using a retroviral vector, and these corrected cells were then infused back into the patient. This is the treatment the assertion refers to.
Now, why must these infusions be periodic? The reason lies in the nature of the cells used. Lymphocytes are a type of white blood cell, but they are not immortal. They have a finite lifespan — they divide, function for a while, and then die. Over time, the population of corrected lymphocytes declines, and the patient’s ADA levels drop again. So the treatment has to be repeated at intervals to maintain a sufficient number of functioning cells.
NoteThe textbook also mentions that later approaches shifted to using bone marrow stem cells for gene therapy, because stem cells can divide throughout life and produce a continuous supply of corrected blood cells — avoiding the need for repeated infusions.
The reason given in the question — “Lymphocytes are immortal” — is simply incorrect. No normal human cell is immortal. Immortality in cells is a property of cancer cell lines (like HeLa cells) or certain stem cells under specific conditions, but not of ordinary lymphocytes. The NCERT does not state that lymphocytes are immortal; in fact, the need for repeated infusions implicitly confirms their limited lifespan. …
- CBSE 2023Set ZOOLOGY1 markMCQQ.When an abnormal gene is replaced by normal gene, what do you call it?(a) Gene mutation(b) Gene cloning(c) Gene therapy(d) Gene ligation
›Reveal solutionSolution
Gene therapy is the technique of correcting a genetic defect by delivering a normal, functional gene to replace or supplement the patient's abnormal (mutant) gene.
Gene therapy is a collection of methods that allow correction of a gene defect diagnosed in a child/embryo. Genetic material (a normal, healthy copy of the gene) is inserted into an individual's cells and tissues to treat a disease caused by a defective (mutant) gene. The classic example taught in NCERT is the treatment of Adenosine Deaminase (ADA) deficiency, caused by the deletion of the gene for ADA, an enzyme crucial for immune function:
- Lymphocytes from the patient's blood are grown in culture outside the body.
- A functional ADA cDNA is introduced into these lymphocytes using a retroviral vector.
- These genetically corrected cells are returned to the patient. …
- CBSE 2023Set ANNUAL1 markQ.Write function of Adenosine deaminase.
›Reveal solutionSolution
ADA breaks down adenosine in purine metabolism; without it, toxic metabolites accumulate and destroy lymphocytes, crippling the immune system - the basis of the first successful gene therapy case.
Adenosine deaminase (ADA) converts adenosine to inosine as part of normal purine metabolism. This function is critical for the proper working of lymphocytes (a type of white blood cell important for the immune system). A genetic deficiency of ADA causes accumulation of toxic deoxyadenosine, which is lethal to lymphocytes, resulting in Severe Combined Immuno-Deficiency (SCID), commonly known as 'bubble boy disease', where the affected individual has little to no functional immune protection.
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- CBSE 2022Set HE2201 markQ.Match the following (Column I with Column II): Gene therapy — choose the matching term from:(a) Obelia(b) Hydra(c) Transgenic(d) Gender linked disease(e) Amoebiasis(f) Antimicrobial substance(g) Male sterilization(h) Genetic disorder.
›Reveal solutionSolution
Gene therapy corrects a genetic defect by introducing a normal, functional copy of the gene, so it matches (h) Genetic disorder; (a) Obelia is the intended distractor.
Gene therapy is a collection of biotechnological methods that correct a genetic defect by delivering a normal, functional gene into a patient's cells to compensate for the non-functional one. The classic example is the treatment of adenosine deaminase (ADA) deficiency, in which a functional ADA gene is introduced into the patient's lymphocytes or bone-marrow stem cells. Because its whole purpose is to treat inherited genetic defects, gene therapy pairs with (h) Genetic disorder.
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