Question

Which step does not involve DNA fingerprinting?
A. Southern blotting
B. Gel electrophoresis
C. Restriction enzyme digestion
D. Northern blotting

Answer 1

The technique of DNA fingerprinting was developed in 1984 by British geneticist Alec Jeffreys. It is a laboratory technique which is used to establish a link between biological evidence and a suspect in a criminal investigation.

Complete answer:
DNA fingerprinting the method of isolating and identifying variable elements within the base-pair sequence of DNA (deoxyribonucleic acid).

The steps of the DNA fingerprinting are:
- The first step in DNA fingerprinting is the extraction of usable 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 lengths.
- 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.
- The agarose gel is mounted on the filter paper wick and the hybridization membrane is sandwiched between the gel and any absorbent material, which draws the transfer buffer through the gel by capillary action. The buffer flow draws 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 the same composition. A photographic film on top of the nylon surface to make a genetic fingerprint.

Northern blotting is used for the transfer of RNA from gels to the membrane to analyze their composition. Since DNA fingerprinting does not study RNA, Northern blotting is not used.

Thus, the correct option is D, Northern blotting.

Note: It is to be noted that VNTRs serves as an important source of RFLP genetic markers. It is used for linkage analysis of genomes. VNTRs produce a pattern of bands unique to each individual. DNA fingerprinting is used to identify criminals related to the forensic department.