Question

What is the first step in Southern blot technique ?
A) Denaturation of DNA on the gel for hybridization with specific probe
B) Production of a group of genetically identical cells
C) Digestion of DNA by restriction enzyme
D) Isolation of DNA from a nucleated cell such as one from the scene of crime

Answer 1

Hint:A Southern blot is a method used in molecular biology for the detection of a specific DNA sequence in DNA sample. The method of Southern blotting is named after the British biologist Edwin Southern who first published it in 1975.

Complete answer:
>First step is isolation of DNA from a nucleated cell such as from the crime scene.
>Restriction endonucleases are then used to cut high molecular weight DNA strands into smaller fragments.
>The DNA fragments are then electrophoresed on agarose gel to separate them by size.
>The method known as alkaline transformer is used.
>Then depending on the direction of the transfer the gel, a sheet of nitrocellulose or alternatively nylon membrane is placed on the top of or below
>In order to permanently attach the transferred DNA to the membrane, the membrane is then exposed to Ultraviolet radiation.
>The membrane is then uncovered to a hybridization probe, a single DNA fragment with a specific sequence and the presence of which in the target DNA is to be determined.
>After hybridization is complete, excess probes are washed from the membrane. The pattern of hybridization is later visualised on X-Ray film by autoradiography.

Hence the correct answer is option( D ).

Note:Protein detection is done by Western blotting.
>RNA detection is done by using the technique known as Northern blotting.
>Southern blotting which is used to detect DNA. Is one of the important processes as it is used in forensic.