Read the passage carefully to answer the questions given below.
Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). In Bacillus thuringiensis the toxin is coded by a gene cryIAc named cry. There are a number of them, for example, the proteins encoded by the genes cryIAc and cryIIAb control the cotton bollworms, that of cryIAb controls corn borer. 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. The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency. This enzyme is crucial for the immune system to function. The disorder is caused due to the deletion of the gene for adenosine deaminase. RNAi takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA.
Which of the following technique is not used for early diagnosis of diseases?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Serum analysis
Early diagnosis means finding a disease while the pathogen is still very low in number, before the symptoms appear. Conventional methods such as serum and urine analysis cannot do this.
Option (1) Recombinant DNA technology — Used for early diagnosis. A labelled probe of DNA or RNA finds its complementary DNA, so a mutated gene can be spotted.
Option (2) Polymerase chain reaction — Used for early diagnosis. PCR amplifies a very small amount of the pathogen’s nucleic acid, e.g. to find HIV in suspected AIDS patients.
Option (3) Serum analysis — Not used for early diagnosis. It is a conventional method; it detects a disease only after the pathogen has multiplied and the symptoms show.
Option (4) Enzyme linked immuno-sorbent assay — Used for early diagnosis. ELISA works on antigen-antibody interaction, detecting the pathogen’s antigens or the antibodies made against it.
Note 1: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
Note 2: The same question was also asked in CUET (UG) 2026 on 30-05-2026 (Slot 2).