PCR: Detection of Pathogens Early — NEET Biology

Correct answer: C — S1, S3 and S5 only

Let's evaluate each statement to identify the NOT correct ones: - **S1. PCR can amplify any type of nucleic acid, including RNA, directly without prior conversion.** This statement is NOT correct. While PCR amplifies nucleic acids, RNA must first be reverse transcribed into cDNA before it can be amplified by PCR (Reverse Transcriptase PCR or RT-PCR). PCR itself directly amplifies DNA, not RNA. - **S2. It is routinely employed for early detection of HIV infection, even when viral load is very low.** This statement is CORRECT. NCERT explicitly states, 'PCR is now routinely used to detect HIV in suspected AIDS patients,' indicating its use for low concentrations. - **S3. PCR relies on antigen-antibody interactions for identifying specific pathogens.** This statement is NOT correct. ELISA relies on antigen-antibody interactions. PCR relies on the amplification of nucleic acids. - **S4. Mutations in genes of suspected cancer patients can be precisely identified by PCR analysis.** This statement is CORRECT. NCERT states, 'It is being used to detect mutations in genes in suspected cancer patients too.' - **S5. The technique can only detect pathogens when symptoms of the disease are clearly visible due to high pathogen concentration.** This statement is NOT correct. PCR is specifically highlighted for its ability to detect pathogens at *very low concentrations* before symptoms are visible, which is an advantage over conventional methods. Therefore, statements S1, S3, and S5 are NOT correct. Option A correctly identifies S1, S3, and S5 as not correct. Options B, C, and D contain incorrect combinations of correct and incorrect statements. The question tests a comprehensive understanding of PCR's principles, capabilities, and its distinction from other diagnostic methods.