Understanding the DNA Fingerprinting Process

DNA fingerprinting, also known as DNA profiling, is a technique used to identify individuals by characteristics of their DNA. It relies on analyzing variations in DNA sequences, particularly repetitive sequences called Variable Number Tandem Repeats (VNTRs). The process involves several key steps performed in a specific order.

Sequence of DNA Fingerprinting Steps

To correctly arrange the steps provided in the question, let's outline the standard procedure for DNA fingerprinting:

1. Isolation of DNA (E): DNA must first be extracted from a biological sample such as blood, saliva, hair roots, skin, or semen.
2. Digestion of DNA by restriction endonucleases (C): The isolated DNA is cut into smaller fragments at specific recognition sites by using restriction enzymes. Different individuals will have different lengths of fragments (Restriction Fragment Length Polymorphism - RFLP) if they have different DNA sequences at or near the restriction sites.
3. Separation of DNA fragments by electrophoresis (B): The DNA fragments produced by restriction digestion are separated based on their size using gel electrophoresis. Smaller fragments move faster and further down the gel than larger ones, creating a pattern of bands.
4. Blotting of separated DNA fragments to nylon (D): The separated DNA fragments from the gel are transferred to a solid support membrane, typically nylon or nitrocellulose. This process is called Southern blotting. This makes the DNA accessible for probing.
5. Hybridisation using labelled VNTR probe (A): Specific DNA probes, which are single-stranded DNA sequences complementary to repetitive regions like VNTRs, are labelled (often with radioactive isotopes or fluorescent dyes) and added to the membrane. These probes bind (hybridize) to the complementary DNA fragments on the membrane, highlighting the specific bands containing VNTRs.

After hybridisation, the membrane is washed to remove unbound probes, and the location of the bound probes is detected (e.g., by autoradiography if radioactive probes are used), producing a pattern of bands characteristic of the individual's DNA.

Arranging the Given Steps

Comparing the standard steps with the options provided:

• (E) Isolation of DNA
• (C) Digestion of DNA by restriction endonucleases
• (B) Separation of DNA fragments by electrophoresis
• (D) Blotting of separated DNA fragments to nylon
• (A) Hybridisation using labelled VNTR probe

The correct sequence of the given steps is therefore (E), (C), (B), (D), (A).

This sequence (E), (C), (B), (D), (A) matches option 2.

Revision Table: DNA Fingerprinting Steps

Additional Information on DNA Fingerprinting

DNA fingerprinting is a powerful tool used in various fields:

• Forensic Science: Identifying suspects or victims in criminal investigations, paternity testing.
• Medical Diagnosis: Detecting inherited diseases.
• Evolutionary Biology: Studying genetic diversity and evolutionary relationships.
• Conservation Biology: Tracking endangered species and managing breeding programs.

The technique relies on the fact that every individual (except identical twins) has a unique DNA profile. The variations in VNTR lengths are highly individual-specific, making the resulting banding pattern a unique 'fingerprint'. Sir Alec Jeffreys developed this technique in 1984.