DNA Fingerprinting - Definition, Principle, Steps, Applications & Diagram

What is DNA Fingerprinting?

DNA Fingerprinting, also known as DNA Profiling, is a procedure that reveals the genetic makeup of any living organism. Differentiation of one person from another is made through variations in their satellite DNA regions. This has brought a revolutionary change in the field of modern science, particularly in forensic and genetic studies.

DNA fingerprinting was first discovered in the 1980s. In 1984, the British geneticist Dr Alec Jeffreys discovered a breakthrough technique, eventually creating a powerful tool for genetic identification and analysis.

DNA fingerprinting is vital in many applications and areas, including forensic science and paternity testing. It is highly applied in the disclosure of crime scenes, diagnosis of genetic diseases, and understanding of biological evolution.

Principles of DNA Fingerprinting

The principle of DNA fingerprinting is that every person has a unique DNA pattern, except identical twins. It studies specific regions in DNA, like VNTRs and STRs, which show differences between individuals. These differences help in identifying people for use in forensics, paternity tests, and biotechnology.

• Genetic Uniqueness

DNA fingerprinting is based on the fact that every person, except for identical twins, will have a unique DNA sequence.

• Polymorphic Regions in DNA

DNA has very polymorphic regions, for instance, Short Tandem Repeats (STRs) and Variable Number Tandem Repeats (VNTRs), that exhibit great differences among individuals and are, therefore, hyper-informative for genetic identification.

Structure of STRs and VNTRs

DNA Fingerprinting Steps

DNA fingerprinting involves a series of steps to identify genetic patterns. These include collecting samples, isolating DNA, cutting it using enzymes, and analyzing it through gel electrophoresis. Each step helps create a unique DNA profile for an individual.

Sample Collection

DNA could be extracted from blood, hair, saliva, and skin cells, amongst others. Care should always be taken to ensure the cleanliness and purity of the sample for the best results.

Isolation of DNA

DNA extraction from preserved samples did not distort or contaminate the sample in any way.

DNA Extraction Process

Digestion of DNA by Restriction Endonucleases

Restriction enzymes work on cutting DNA at precise recognition sites, thereby creating a specific pattern of DNA fragments. The DNA fingerprint is then composed of these fragments.

The action of Restriction Endonucleases on DNA

Gel Electrophoresis

DNA fragments are sorted by size using agarose gel electrophoresis and an electric field. This step images the DNA bands.

Blotting

The DNA fragments are transferred from the gel onto a nylon or nitrocellulose membrane in preparation for hybridisation.

Hybridisation Using Labelled Probe

The transferred membrane strands of DNA are exposed to labelled DNA probes, which are complementary to the known DNA sequences to be measured. The unique DNA patterns are thus highlighted.

Autoradiography

Autoradiography exposes the radiolabeled DNA probes to the separated fragments of DNA on the membrane, revealing unique DNA band patterns for different individuals.

Techniques of DNA Fingerprinting

Different techniques are used to perform DNA fingerprinting based on the type of sample and purpose. Common methods include RFLP, PCR, STR analysis, and mitochondrial DNA testing. Each technique has its own advantages in terms of speed, accuracy, and sensitivity. The methods of DNA fingerprinting are described below:

RFLP (Restriction Fragment Length Polymorphism)

RFLP studies the variability in the lengths of DNA fragments digested by restriction enzymes. This technique, although not in use so frequently at present, was one of the earliest methods of DNA profiling.

PCR (Polymerase Chain Reaction)

PCR helps to amplify desired DNA fragments, making it possible to look for analysis in very small amounts of DNA. PCR is a popular technique, as it is fast and very sensitive.

STR Analysis

Short Tandem Repeats (STR) analysis is the most commonly used technique at present for DNA fingerprinting. It studies only specific areas of DNA that show hypervariability between individuals.

Mitochondrial DNA Analysis

Mitochondrial DNA analysis is used for studying ancient DNA and tracing the maternal lineage. It can often be the only source of DNA in forensic applications due to the lack of DNA in the nucleus.

Applications of DNA Fingerprinting

DNA fingerprinting is used in many fields like forensic science, medicine, and research. It helps identify criminals, prove biological relationships, and diagnose genetic diseases. It is also useful in studying human evolution and biodiversity.

• Forensic Science

It is an essential technique in forensic science for use in crime scene investigations and paternity testing.

• Medical Applications

It is involved in the clinical diagnosis of genetic disorders and matching tissues for transplants to develop a personalized medicine system.

• Biological Research

In evolutionary biology and population genetics, DNA fingerprinting studies genetic variability and the evolutionary relationship among species.

DNA Fingerprinting Practice Questions for NEET

Q1. On average, how many percent of the DNA between two humans is the same?

1. 99%

2. 99.9%

3. 95%

4. 100%

Correct answer: 2) 99.9%

Correct answer:

In terms of DNA composition, all humans are 99.9% genetically similar, with the differences confined to the remaining 0.1%. This small variation plays a crucial role in determining individual traits and susceptibility to diseases. The genetic differences in this 0.1% provide valuable insights into the causes of various diseases, as they often include mutations, polymorphisms, or variations that influence health, response to treatments, and disease risk.

Hence the correct answer is option 2) 99.9%

Q2. Who developed the DNA Fingerprinting technique?

1. Alec Jeffreys

2. Francis Crick

3. James Watson

4. None of above

Correct answer: 1) Alec Jeffreys

Explanation:

Sir Alec Jeffreys was the first to construct DNA fingerprinting in the 1980s, based at the University of Leicester as both a professor and a geneticist. He used satellite DNAs, more scientifically referred to as variable number tandem repeats (VNTRs), in detecting differences in the genetics of different humans. This innovative method allowed the efficient detection of individuals and turned criminal investigations and paternity testing upside down by comparing the samples with unique genetic profiles.

Hence the correct answer is Option 1) Alec Jeffreys.

Q3. Choose the correct flow of DNA fingerprinting steps:

1. Isolating the DNA→Digesting the DNA→Separating the digested fragments→Blotting the separated fragments→Hybridising the fragments→ Analysing the hybrid fragments

2. Isolating the DNA→Separating the digested fragments→Digesting the DNA→Blotting the separated fragments→Hybridising the fragments→ Analysing the hybrid fragments

3. Isolating the DNA→Separating the digested fragments→Digesting the DNA→Hybridising the fragments→Blotting the separated fragments→ Analysing the hybrid fragments

4. Isolating the DNA→Digesting the DNA→Separating the digested fragments→Hybridising the fragments→ Blotting the separated fragments→Analysing the hybrid fragments

Correct answer: 1) Isolating the DNA→Digesting the DNA→Separating the digested fragments→Blotting the separated fragments→Hybridising the fragments→ Analysing the hybrid fragments

Explanation:

DNA isolation: Extracting DNA from a sample (such as blood, hair, etc.) is the initial step.

DNA digestion: Using specialized enzymes known as restriction enzymes, which can identify and cut DNA at particular sequences, the extracted DNA is subsequently broken up into smaller pieces.

Sorting the digested fragments: A method known as gel electrophoresis is used to separate the DNA fragments based on size. Larger fragments pass through the gel more slowly than smaller ones.

Blotting the separated fragments: Southern blotting is the act of transferring the separated DNA fragments onto a membrane, often a nitrocellulose or nylon membrane.

Hybridizing the fragments: To identify the DNA fragments of interest, the membrane containing the fragments is subsequently exposed to a tagged probe, which is a brief DNA sequence complementary to a particular sequence in the DNA fragments.

Analyzing the hybrid fragments: The DNA fingerprint is created by analyzing the patterns of the hybridized fragments after the tagged probe has been found. Each person has a pattern.

Hence, the correct answer is option 1)Isolating the DNA → Digesting the DNA → Separating the digested fragments → Blotting the separated fragments → Hybridising the fragments → Analysing the hybrid fragments.

Also Read:

• MCQs on DNA Fingerprinting

• Difference between Restriction Endonuclease and Exonuclease

• Bioremediation

FAQs on DNA Fingerprinting

Q1. What is DNA fingerprinting?

It is a genetic technique that identifies individuals based on unique DNA patterns, especially VNTRs and STRs.

Q2. What is the principle behind DNA fingerprinting?

The principle is based on polymorphism in DNA sequences, where individuals have unique patterns in repetitive DNA regions.

Q3. What are the main steps involved in DNA fingerprinting?

The main steps are sample collection, isolation of DNA, digestion of DNA by restriction enzyme, separation by gel electrophoresis, hybridization with DNA probes, and autoradiography.

Q4. What are the major applications of DNA fingerprinting?

Major applications include criminal identification, paternity testing, identifying remains, and studying genetic diversity.

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