Question

Which step does not involve in DNA finger printing?

• A. Southern blotting
• B. Gel electrophoresis
• C. Restriction enzyme digestion
• D. Northern blotting

Answer 1

Answer: (D)

Northern blotting

The first step in DNA finger printing is extraction of useable DNA followed by its digestion with restriction enzymes to produce the restriction fragments length polymorphisms, or RFLPs. The DNA fragments are called RFLPs because depending on the location of restriction sites, the restriction enzymes produce DNA fragments with different length. The fragments are then sorted according to size by gel electrophoresis. An electric field is applied to gel that makes the negatively charged molecules through a matrix of gel. The molecules move according to their size. The DNA fragments are then transferred from the gel to the surface of the nylon via southern blotting. For the purpose, the agarose gel is mounted on filter-paper wick and the hybridization membrane is sandwiched between the gel and any absorbent material, which draw the transfer buffer through the gel by capillary action. The buffer flow draw the DNA molecules which are then immobilized on the synthetic membrane. Finally, radioactive probes are washed over the nylon surface to allow their joining to any DNA fragments of same composition. A photographic film on top of the nylon surface to make a genetic fingerprint. Northern blotting is used for transfer of RNA from gels to membrane to analyze their composition. Since DNA fingerprinting does not study RNA, Northern blotting is not used. Correct answer is D.