Question:

What is the first step in the Southern Blot technique?

Updated On: Aug 1, 2022
  • Denaturation of DNA on the gel for hybridization with specific probe
  • Production of a group of genetically identical cells
  • Digestion of DNA by restriction enzyme
  • Isolation of DNA from a nucleated cell such as the one from the scene of crime
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The Correct Option is D

Solution and Explanation

A Southern blot is a method used for detection of a specific DNA sequence in DNA samples. This method combines transfer of electrophoresis-separated DNA fragments to a filter membrane and subsequent fragment detection by probe hybridization. The first step in a Southern blot is to isolate the DNA from the cells collected from the crime scene. The next step would be to prepare the DNA mixture by breaking it into small fragments using a protein called a restriction enzyme. The mixture of DNA fragments is then separated according to size by way of a technique called gel electrophoresis. Following separation, the double-stranded pieces of DNA are denatured, or separated, into single strands within the gel. Next, the DNA is transferred from the gel onto a blotting membrane. This step is what gives the technique the name Southern blotting So, the correct answer is 'Isolation of DNA from a nucleated cell such as the one from the scene of crime'
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DNA Fingerprinting

​​DNA fingerprinting, also called DNA typing, DNA profiling, genetic fingerprinting, genotyping, or identity testing, in genetics, method of isolating and identifying variable elements within the base-pair sequence of DNA.

The procedure of DNA Fingerprinting:

The procedure for creating a DNA fingerprint consists of first obtaining a sample of cells, such as skin, hair, or blood cells, which contain DNA. The DNA is extracted from the cells and purified. In Jeffreys’s original approach, which was based on restriction fragment length polymorphism (RFLP) technology, the DNA was then cut at specific points along the strand with proteins known as restriction enzymes. The enzymes produced fragments of varying lengths that were sorted by placing them on a gel and then subjecting the gel to an electric current (electrophoresis): the shorter the fragment, the more quickly it moved toward the positive pole (anode). The sorted double-stranded DNA fragments were then subjected to a blotting technique in which they were split into single strands and transferred to a nylon sheet. The fragments underwent autoradiography in which they were exposed to DNA probes—pieces of synthetic DNA that were made radioactive and that bound to the minisatellites. A piece of X-ray film was then exposed to the fragments, and a dark mark was produced at any point where a radioactive probe had become attached. The resultant pattern of marks could then be analyzed.