Complete guide on DNA fingerprinting techniques, history, application

DNA fingerprinting is a molecular technique used to detect variations in the DNA sequence, primarily through repetitive regions called “microsatellites” or “short tandem repeats” (STRs). By analyzing these repetitive sequences, a unique pattern (or “fingerprint”) is generated for each individual.

DNA fingerprinting, also known as DNA profiling or genetic fingerprinting, is a technique used to identify an individual by analyzing the unique patterns in their DNA. The method is based on the fact that although all humans share about 99.9% of their DNA, the remaining 0.1% is unique to each individual (except for identical twins). This 0.1% variation is what makes DNA fingerprinting a powerful tool for identification purposes

Brief history of DNA fingerprinting

in 1984, The technique of DNA fingerprinting was first developed by British scientist Sir Alec Jeffreys at the University of Leicester. He discovered that certain regions of DNA were highly variable among individuals.
He demonstrated its usefulness in human identification, particularly in paternity testing and forensic investigations.
DNA fingerprinting was first used in a criminal case in the UK, where it helped solve a double murder case by matching DNA found at the crime scene to a suspect.

In India DNA fingerprinting is explored by Prof. Lalji Singh, and he is called the father of Indian DNA fingerprinting.

Principle of DNA fingerprinting

DNA fingerprinting is based on the principle that each individual has a unique DNA sequence. It focuses on specific regions of DNA that vary greatly between people. The process involves extracting DNA, cutting it into fragments, amplifying certain regions, and then separating the fragments by size. The resulting pattern of DNA fragments, known as a “fingerprint,” is unique to each person and can be used for identification, such as in criminal investigations or paternity testing.

Techniques involved in DNA fingerprinting

DNA fingerprinting involves a series of laboratory techniques, which are as follows:

1. Collection of Sample: DNA can be extracted from blood, hair, semen, skin, saliva, or other bodily fluids or tissues.
2. DNA Extraction: The DNA is isolated from the cells using chemical solutions or mechanical methods. The extracted DNA is then purified.
3. Restriction Enzyme Digestion: The extracted DNA is cut into smaller fragments by using restriction enzymes. These enzymes target specific DNA sequences, cutting the DNA at particular sites.
4. Gel Electrophoresis: The DNA fragments are then separated by size using a technique called gel electrophoresis. This process uses an electric field to move the negatively charged DNA fragments through an agarose gel matrix. Smaller fragments move faster, while larger fragments move slower, creating a unique banding pattern.
5. Southern Blotting (Traditional method): The separated DNA fragments are transferred to a membrane and hybridized with a labeled probe (a short DNA sequence) that binds to specific regions of the DNA.
6. Polymerase Chain Reaction (PCR): In modern DNA fingerprinting, PCR is used to amplify specific regions of the DNA, such as STRs (short tandem repeats). PCR allows for the analysis of very small DNA samples, making it more efficient and faster than older methods.
7. DNA Sequencing: In some cases, DNA sequencing methods (like Sanger sequencing or Next-Generation Sequencing) are used for detailed analysis of the DNA fragments.

methods of dna fingerprinting | Process or Steps of DNA fingerprinting

DNA fingerprinting involves several key steps to analyze the unique DNA patterns of an individual. Here’s a simple breakdown of the main methods:

• DNA Extraction: The first step is to extract DNA from a sample (like blood, hair, or saliva). This is done by breaking open the cells and isolating the DNA.
• DNA Fragmentation: The extracted DNA is then cut into smaller pieces using special enzymes called restriction enzymes. These enzymes target specific sequences of DNA, cutting it at precise locations.
• Amplification (PCR): Specific DNA regions, especially those that vary between individuals, are copied many times using a technique called Polymerase Chain Reaction (PCR). PCR makes millions of copies of these regions, so they can be studied easily.
• Gel Electrophoresis: The amplified DNA is placed into a gel and an electric current is applied. The DNA fragments move through the gel, with smaller pieces traveling further than larger ones. This creates a pattern of bands.
• Analysis: The banding pattern is compared to others. Each person has a unique pattern, which is like a DNA “fingerprint.” This pattern can be used to identify individuals or determine relationships.

These steps together help in creating a unique DNA profile that can be used in forensic investigations, paternity tests, and other forms of genetic identification

You may be having question like earlier section (techniques involved in DNA fingerprinting), why some of the techniques is missing in these steps above.

There are different types of, or we can say method to do DNA fingerprinting for various types of objectives. the above-mentioned method is one of the common steps (e.g. AFLP/RAPD etc.).

Fragmentation can be excluded in case of RAPD method. based on depth of information one whould like to seek method, its steps and technique involved vary.

see one of the other methods below (diagram of dna fingerprinting)

Mechanism of DNA Fingerprinting

The process of DNA fingerprinting exploits regions of the genome that vary greatly between individuals, especially repetitive DNA sequences such as

• Short Tandem Repeats (STRs) – short, repeated sequences of 2-6 base pairs of DNA. The number of repeats at a given STR locus varies between individuals, creating a unique pattern. and
• Variable Number Tandem Repeats (VNTRs)- These are larger repeated sequences of DNA that also vary in number between individuals.

these repetitive regions produce fragments of different lengths depending on the number of repeats, forming a distinctive “banding pattern” on a gel electrophoresis or through PCR amplification.

This pattern is unique for the studied individuals/organism/species and can be used to identify the organism or individual just like our fingerprint.

Applications of DNA Fingerprinting | dna fingerprinting uses

There is various application of dna fingerprinting technology in different area of biological science. Some of the application of dna fingerprinting are –

• Forensic Science: DNA fingerprinting is widely used in criminal investigations to match DNA samples from crime scenes (blood, hair, etc.) with suspects or databases. It can be used to prove or disprove the presence of a suspect at a crime scene.
• Paternity Testing: By comparing the DNA of a child with that of the mother and the potential father, paternity can be established with high accuracy.
• Identification of Human Remains: DNA fingerprinting is used to identify human remains in cases of natural disasters, war, or mass fatalities.
• Immigration and Kinship Analysis: DNA testing can help prove family relationships for purposes like immigration and inheritance.
• Conservation Biology: It is used to track genetic diversity and monitor the breeding patterns of endangered species.
• Genealogy and Ancestry Testing: Commercial DNA tests now allow individuals to trace their lineage and family history using genetic markers.
• Medical Genetics: In some cases, DNA fingerprinting can help in diagnosing genetic disorders or understanding inherited diseases.

Challenges in DNA Fingerprinting

Despite its usefulness, there are several challenges and limitations associated with DNA fingerprinting:

• Sample Contamination: The accuracy of the results can be compromised if the DNA sample is contaminated with foreign DNA (e.g., from another person or environmental sources).
• Degraded Samples: DNA extracted from old or degraded samples (e.g., from skeletal remains or crime scene evidence) can be difficult to analyze.
• Ethical Issues: The use of DNA databases raises concerns about privacy and the potential for misuse of personal genetic information.
• Cost and Time: Although advancements like PCR have made the process faster, DNA fingerprinting can still be expensive and time-consuming, especially for high-throughput testing.
• Incomplete or Missing Data: In some cases, not all the required genetic markers may be available or clear enough to generate a conclusive fingerprint.

Important question for examination

One-Line Questions:

• What is the principle behind DNA fingerprinting?
• Who is known as the father of DNA fingerprinting?
• How is DNA fingerprinting used in criminal investigations?

Short questions :

• What are the main techniques involved in DNA fingerprinting?
• How does the mechanism of DNA fingerprinting work?
• What are the key steps in the process of DNA fingerprinting?

Assay type questions

• Explain the history and development of DNA fingerprinting and its impact on forensic science.
• Discuss the various methods and techniques used in DNA fingerprinting, including PCR and gel electrophoresis.
• Describe the applications of DNA fingerprinting in fields such as paternity testing, criminal investigations, and medical research.

References

https://scind.org/History/article/Prof-Lalji-Singh-Father-Of-Indian-DNA-Fingerprinting-Technology

https://www.researchgate.net/publication/344508069_DNA_FINGERPRINTING

DNA fingerprinting lecture 38 NPTEL

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