Question

Pick the incorrect statements among the following.
(i) PCR is one of the techniques used in DNA fingerprinting.
(ii) PCR can be used for detection of a specific mutation or pathogen.
(iii) Alec Jeffreys won the Nobel Prize for the development of polymerase chain reaction (PCR).
(iv) DNA primers are designed such that they can attach anywhere on the DNA segment which has to be amplified.

• A. i, iv
• B. i, ii, iii
• C. i, ii, iv
• D. iii, iv

Answer 1

The correct option is D iii, iv

Polymerase chain reaction (PCR) is a method for the amplification of specific DNA sequences.

There are three steps in PCR:

- Denaturation: The two strands of double stranded DNA are separated using high temperature (96℃).

- Annealing: As DNA polymerisation reaction needs a 3' free OH end of nucleotide, primers are added to serve the purpose. The designed primers are single-strand sequences of DNA around 20 to 30 bases in length. They are designed such that they bind to the specific segment of DNA which needs to be amplified. They are allowed to anneal to the complementary sequences of template DNA during this step of PCR, maintaining the annealing temperature around 55-65℃ .

- Extension: DNA-dependent DNA polymerase is used for extension of the primers and elongation of new chains. Thermostable DNA polymerases like the Taq polymerase are used for this process.

Kary Mullis is accredited with the discovery of PCR, who received the Nobel prize for the same.

Alec Jeffreys developed the DNA fingerprinting technique. DNA fingerprinting is a laboratory technique which helps in identifying a person based on the unique repetitive sequence in his DNA.

Polymerase chain reaction (PCR) is a step in DNA fingerprinting that helps to amplify the DNA sample even if it is available in a very small amount.

Viral DNA can be detected by PCR using primers specific to the target sequence. Hence it can be used for diagnostic analysis. Being highly sensitive, it helps in early detection of virus after infection or on onset of disease. Mutation can also be detected by PCR.