Which of the following is NOT an application of PCR ?

The correct answer is Option (4) → To cure ADA (adenosine deaminase) deficiency

Option (1) Paternity testing — An application of PCR. PCR amplifies DNA for DNA fingerprinting, which settles paternity disputes.

Option (2) Detection of mutations of genes in suspected cancer patient — An application of PCR. PCR amplifies even a very small amount of DNA, so a mutated gene can be found early. It is used in this way in suspected cancer patients.

Option (3) Powerful technique to identify genetic disorder — An application of PCR. PCR is a powerful technique to identify many genetic disorders.

Option (4) To cure ADA (adenosine deaminase) deficiency — Not an application of PCR. ADA deficiency is treated by gene therapy, enzyme replacement or bone marrow transplant. PCR only detects DNA; it cures nothing.

NCERT Extract:
Molecular Diagnosis – “… Using conventional methods of diagnosis (serum and urine analysis, etc.) early detection is not possible. Recombinant DNA technology, Polymerase Chain Reaction (PCR) and Enzyme Linked Immuno-sorbent Assay (ELISA) are some of the techniques that serve the purpose of early diagnosis. Presence of a pathogen (bacteria, viruses, etc.) is normally suspected only when the pathogen has produced a disease symptom. By this time the concentration of pathogen is already very high in the body. However, very low concentration of a bacteria or virus (at a time when the symptoms of the disease are not yet visible) can be detected by amplification of their nucleic acid by PCR. … PCR is now routinely used to detect HIV in suspected AIDS patients. It is being used to detect mutations in genes in suspected cancer patients too. It is a powerful techqnique to identify many other genetic disorders.”
DNA Fingerprinting – “… Since DNA from every tissue (such as blood, hair-follicle, skin, bone, saliva, sperm etc.), from an individual show the same degree of polymorphism, they become very useful identification tool in forensic applications. Further, as the polymorphisms are inheritable from parents to children, DNA fingerprinting is the basis of paternity testing, in case of disputes.”
Gene Therapy – “… The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency.”