Q.PCR is a useful tool for early diagnosis of an Infectious disease. Elaborate.

Step 1. Explain the underlying limitation PCR solves: pathogens like viruses and bacteria are usually detected by conventional methods only once they have produced visible symptoms, by which time the pathogen concentration in the body is already very high — but PCR can detect even a very low concentration of a pathogen, before symptoms appear at all, by amplifying its nucleic acid. Step 2. Explain the diagnostic logic: if a pathogen is present in a clinical specimen (blood, stool, spinal fluid, sputum), its DNA will be present too, and PCR can amplify unique sequences in that DNA using primers specific to the pathogen, producing enough copies to detect reliably even from a trace starting amount. Step 3. Note that traditional identification methods instead require culturing the organism from the specimen and running metabolic/biochemical tests, which takes time the patient may not have and does not work for organisms that are slow-growing or hard to culture; PCR bypasses culturing entirely. Step 4. Give concrete clinical applications: PCR diagnoses inherited disorders prenatally from chorionic villi or amniocentesis samples (sickle cell anaemia, beta-thalassemia, phenylketonuria); RT-PCR (after converting RNA to cDNA via reve …

Contrast PCR's nucleic-acid amplification approach against conventional culture-based detection, then support the point w …

• Describing PCR generically as 'a DNA copying technique' without connecting that capability to WHY it enables earlier diagnosis than conventional methods. …