Q. 20 Can a disease be detected before its symtoms appear? Explain the principle involved.

When the symptoms of the disease are not yet visible,the pathogen concentration is very low so, the detection by conventional diagnostic tests is very difficult.

However, detection of a disease before the appearance of symptoms is possible by the amplification of victim's nucleic acid by PCR

The principle involved here is that a single DNA molecule can be copied endlessly in a test tube using primers, DNA polymerase enzyme and free nucleotides. The desired DNA of the pathogen is amplified by PCR from a limited amount of DNA template.