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 crylAc named cry. There are a number of them, for example, the proteins encoded by the genes crylAc and cryllAb control the cotton bollworms, that of crylAb 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?

Serum analysis

The correct answer is Option (3) → Serum analysis 

Early diagnosis and understanding the pathophysiology of a disease are crucial for effective treatment. Conventional diagnostic methods, such as serum and urine analysis, may not always lead to early detection. However, modern techniques like Recombinant DNA technology, Polymerase Chain Reaction (PCR), and Enzyme Linked Immuno-sorbent Assay (ELISA) have proven effective in achieving early diagnosis.

Typically, the presence of a pathogen (bacteria, viruses, etc.) is suspected only after disease symptoms have manifested. By this time, the pathogen concentration in the body is already high. However, PCR, a sensitive molecular technique, enables the detection of even low concentrations of pathogens before visible symptoms appear. PCR has become a routine tool in diagnosing HIV in suspected AIDS patients and identifying mutations in genes among suspected cancer patients. Moreover, PCR is a valuable technique for identifying various genetic disorders.

ELISA is based on the principle of antigen-antibody interaction. Infection by pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc.) or by detecting the antibodies synthesised against the pathogen.