List the various markers that are used in DNA finger printing.

NCERT Exemplar · Q70

Q. List the various markers that are used in DNA finger printing.

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Concept understanding — DNA Fingerprinting

DNA Fingerprinting: A Beginner's Guide

Imagine you have a unique signature — not your name, not your face, but something written in every cell of your body. That is your DNA. And just like a fingerprint on your fingertip, this DNA signature is different for every person (except identical twins). DNA fingerprinting is the technique that reads that signature.

The Everyday Intuition

Think of a barcode on a product. Every product has a unique pattern of black lines. A scanner reads that pattern to identify exactly which product it is. Your DNA works the same way — it is a long, coiled molecule inside your cells, and certain regions of it have repeating patterns that vary from person to person. DNA fingerprinting scans those repeating patterns and creates a "barcode" unique to you.

What the NCERT Textbook Says

The NCERT Class 12 Biology textbook defines DNA fingerprinting as a technique used to identify the differences in the DNA sequences of individuals. It focuses on Variable Number Tandem Repeats (VNTRs) — short, repeating sequences of DNA that are scattered throughout our genome. The number of repeats at a particular location varies greatly between people. Two unrelated individuals are extremely unlikely to have the same number of repeats at the same locations.

Note

DNA fingerprinting does not read your entire DNA sequence. It only looks at a few specific spots where the repeats vary a lot between people. This makes it fast and practical.

How It Works (Simplified)

The process has a few key steps, but you don't need to memorise every chemical name. Focus on the logic:

Extract DNA from a sample — blood, hair, saliva, or even a tiny skin cell.
Cut the DNA at specific points using special enzymes (called restriction enzymes). This chops the long DNA into fragments of different lengths.
Separate the fragments by size using a technique called gel electrophoresis. Smaller fragments move faster through a gel, so they end up farther from the starting point.
Transfer the fragments onto a nylon membrane (Southern blotting).
Probe the membrane with a radioactive or fluorescent probe that sticks only to the VNTR regions. This reveals a pattern of bands — like a barcode.
Compare the patterns between samples.

Why It Matters

DNA fingerprinting is not just a lab curiosity. It has real-world applications that you will encounter in exams and in life:

Forensic science: Matching crime scene evidence (blood, hair, semen) to a suspect. This is what you see in crime shows — but it is real.
Paternity testing: A child's DNA fingerprint is a mix of the mother's and father's. By comparing bands, you can determine biological parenthood with near-certainty.
Identifying victims: After disasters (earthquakes, plane crashes), DNA fingerprinting helps identify bodies when other methods fail.
Studying evolution: Comparing DNA fingerprints of different species reveals how closely related they are.

Important

DNA fingerprinting is not the same as DNA sequencing. Sequencing reads the entire order of bases (A, T, G, C). Fingerprinting only looks at the pattern of fragment lengths. It is faster and cheaper, but gives less detailed information.

A Common Misunderstanding …

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DNA fingerprinting primarily relies on Variable Number Tandem Repeats (VNTRs), which are short, repetitive DNA sequences that vary significantly in number among individuals, creating a unique genetic profile.

DNA fingerprinting is a revolutionary technique that allows for the identification of individuals based on their unique DNA patterns. Just as no two individuals (except identical twins) share the exact same fingerprints on their hands, their DNA sequences also exhibit unique variations. This method harnesses these variations, particularly in specific regions of the genome, to create a distinctive genetic profile for each person. The underlying principle is that while the vast majority of our DNA is identical across all humans, certain segments show considerable differences, making them ideal "markers" for identification.

A significant portion of the human genome consists of what is known as repetitive DNA. Unlike genes that code for proteins, these sequences do not directly contribute to protein synthesis. Instead, they are stretches of DNA that are repeated many times over. These repetitive DNA sequences can be separated from the bulk genomic DNA as different peaks during density gradient centrifugation, and are thus called satellite DNA. The key to DNA fingerprinting lies in the variability within these repetitive sequences.

The primary markers used in DNA fingerprinting are Variable Number Tandem Repeats (VNTRs).

Nature of VNTRs: VNTRs are a type of satellite DNA. They are short nucleotide sequences that are arranged tandemly, meaning they are repeated one after another in a continuous stretch. The length of these repeats can vary, but they are typically between 11 and 60 base pairs long.
Variability: The crucial aspect of VNTRs is that the number of times these specific sequences are repeated differs significantly from one individual to another. For example, one person might have a particular VNTR sequence repeated 10 times at a specific locus on a chromosome, while another person might have it repeated 15 times at the same locus. This variation in the number of repeats is what makes them so useful as markers.
Inheritance: VNTRs are inherited from parents. An individual receives one set of VNTRs from their mother and another from their father. This biparental inheritance means that each person has a unique combination of VNTR lengths, creating a highly individualistic pattern. …

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Q.List the various markers that are used in DNA finger printing.

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