DNA Fingerprinting: DNA Profiling, VNTR, STR, Steps & Uses
DNA Fingerprinting: DNA Typing, DNA Profiling, Steps, Uses and Southern Blotting
DNA fingerprinting, also known as DNA typing or DNA profiling, is a molecular biology technique used to identify individuals based on differences in specific repetitive DNA sequences. It has important applications in forensic science, paternity testing, and biological research.
What is DNA Fingerprinting?
Most of the DNA sequence is similar among humans, but a small portion differs between individuals. These variable regions often contain repeated DNA sequences known as satellite DNA.
DNA fingerprinting involves the isolation and analysis of these variable DNA regions. The DNA fragments are separated according to their size, transferred to a membrane by Southern blotting, and detected using specific DNA probes. The resulting pattern of bands is called a DNA fingerprint.
Types of Repetitive DNA Used in DNA Profiling
1. VNTR – Variable Number Tandem Repeats
- VNTR stands for Variable Number Tandem Repeats.
- The technique was pioneered by Alec Jeffreys.
- VNTR regions contain repeated sequences of DNA.
- The number of repeats varies between individuals.
- These regions can therefore be used for DNA identification.
2. STR – Short Tandem Repeats
- STR stands for Short Tandem Repeat.
- STRs are short repeated DNA sequences.
- They are also commonly referred to as microsatellites.
- The number of repeats can vary among individuals.
- STR analysis is widely used in modern forensic DNA profiling.
DNA Fingerprinting in India
- Father of DNA fingerprinting: Alec Jeffreys
- Father of DNA fingerprinting in India: Lalji Singh
- DNA fingerprinting technology was introduced in India by Lalji Singh.
- DNA fingerprinting research in India has been associated with CCMB, Hyderabad (Centre for Cellular and Molecular Biology).
Steps of DNA Fingerprinting
1. Isolation of DNA
DNA is isolated from cells containing a nucleus. Biological samples that may provide DNA include:
- White blood cells (WBCs)
- Hair follicles
- Sperm cells
- Other biological samples containing DNA
2. Digestion of DNA
The isolated DNA is cut into smaller fragments using specific restriction endonucleases. This step is also called restriction digestion.
3. Amplification of DNA
The required DNA regions can be amplified using PCR (Polymerase Chain Reaction). PCR produces many copies of the selected DNA region, making it easier to analyse.
4. Separation of DNA Fragments by Gel Electrophoresis
The DNA fragments are separated according to their size using gel electrophoresis. Agarose gel is commonly used for separating DNA fragments.
Smaller DNA fragments generally move faster through the gel than larger fragments.
5. Denaturation of DNA
The separated DNA is converted into single-stranded DNA. Denaturation can be achieved using heat or alkaline treatment.
6. Southern Blotting
In the classical DNA fingerprinting method, DNA fragments separated on a gel are transferred to a membrane such as a nylon membrane or nitrocellulose membrane. This transfer process is known as Southern blotting.
The technique is named after its developer, Edwin M. Southern.
7. Hybridisation with a DNA Probe
A labelled DNA probe is used to identify complementary repetitive DNA sequences.
DNA probe: A probe is a single-stranded DNA molecule containing a nucleotide sequence complementary to the target DNA sequence.
The probe binds to its complementary sequence through hybridisation.
8. Autoradiography and Detection
In the classical method, labelled DNA fragments are detected by autoradiography. The hybridised regions produce visible bands on the detection film, generating a characteristic DNA banding pattern.
DNA Fingerprinting Applications
DNA fingerprinting has several important applications in biology and forensic science.
1. Forensic Science
DNA profiles obtained from biological evidence can be compared with DNA profiles from individuals during forensic investigations.
2. Paternity and Maternity Testing
DNA profiling can be used to establish biological relationships, including disputed paternity and maternity cases.
3. Identification of Individuals
DNA profiles can help identify individuals from suitable biological samples.
4. Population and Evolutionary Studies
DNA variation can also be studied to investigate genetic relationships, population variation and evolutionary patterns.
Southern, Northern and Western Blotting
Different blotting techniques are used to study different biological molecules.
| Technique | Main Target |
|---|---|
| Southern blotting | DNA |
| Northern blotting | RNA |
| Western blotting | Protein |
Southern → DNA
Northern → RNA
Western → Protein
DNA Fingerprinting: Quick Revision
- DNA fingerprinting is also called DNA typing or DNA profiling.
- It analyses variable regions of DNA.
- VNTR means Variable Number Tandem Repeats.
- STR means Short Tandem Repeats.
- Alec Jeffreys pioneered DNA fingerprinting.
- Lalji Singh is known as the father of DNA fingerprinting in India.
- DNA fragments can be separated by gel electrophoresis.
- Southern blotting is used for DNA detection.
- A labelled DNA probe detects complementary target sequences.
- DNA fingerprinting has applications in forensic science and relationship testing.
Frequently Asked Questions (FAQs)
What is DNA fingerprinting?
DNA fingerprinting is a technique used to identify individuals by analysing variable DNA sequences and generating a characteristic DNA profile.
Who discovered DNA fingerprinting?
Alec Jeffreys pioneered DNA fingerprinting.
Who is the father of DNA fingerprinting in India?
Lalji Singh is widely known as the father of DNA fingerprinting in India.
What is VNTR?
VNTR stands for Variable Number Tandem Repeats. These are repetitive DNA sequences in which the number of repeats varies among individuals.
What is Southern blotting used for?
Southern blotting is a molecular biology technique used to detect specific DNA sequences after separation of DNA fragments by gel electrophoresis.
Which blotting technique is used for RNA?
Northern blotting is used for the detection and analysis of RNA.
Which blotting technique is used for proteins?
Western blotting is used for the detection and analysis of proteins.
Conclusion
DNA fingerprinting is an important application of molecular biology that uses variation in repetitive DNA sequences to generate an individual-specific DNA profile. The classical method involves DNA isolation, restriction digestion, electrophoresis, denaturation, Southern blotting, hybridisation and detection. Its applications include forensic identification, relationship testing and genetic research.
Keywords: DNA fingerprinting, DNA profiling, DNA typing, VNTR, STR, satellite DNA, Southern blotting, DNA fingerprinting steps, DNA fingerprinting applications, Alec Jeffreys, Lalji Singh, forensic DNA analysis, DNA profiling for paternity test, NEET Biology, molecular biology notes
