Gene therapy is a collection of methods for :

The correct answer is Option (4) → Correcting a genetic defect diagnosed in a child or embryo

Option (1) Correcting physiological defects — Incorrect. Too broad: gene therapy corrects only defects caused by a faulty gene.

Option (2) Correcting morphological defects — Incorrect. Morphological defects are defects of body form or shape. Gene therapy does not target body form; it corrects a defect in a gene by inserting normal genes into the person’s cells.

Option (3) Treating blood related disorders — Incorrect. The first case (ADA deficiency) was an immune disorder, but gene therapy is not limited to blood.

Option (4) Correcting a genetic defect diagnosed in a child or embryo — Correct. Gene therapy is a set of methods for correcting a gene defect diagnosed in a child or embryo. A normal gene is put into the person’s cells to take over the job of the faulty gene.

NCERT Extract:
Gene Therapy – “If a person is born with a hereditary disease, can a corrective therapy be taken for such a disease? Gene therapy is an attempt to do this. Gene therapy is a collection of methods that allows correction of a gene defect that has been diagnosed in a child/embryo. Here genes are inserted into a person’s cells and tissues to treat a disease.”