DNA Fingerprinting — Complete Concept
A comprehensive exploration of how the tiniest fraction of genetic difference makes every individual unique — and how science harnesses that uniqueness for identification, forensics, and evolutionary insight.
The Core Idea Behind Individual Uniqueness
How Similar Are We?
99.9% DNA is the same among all humans
Genome size ≈ 3 × 10⁹ base pairs
Difference calculation:
0.1% of 3×10⁹ = 3×10⁶
👉 So ~3 million base differences make each person unique.
That Tiny Fraction Creates Differences In:
  • Face shape
  • Height
  • Metabolism
  • Disease susceptibility
  • Fingerprints
  • Behaviour tendencies

Insight: That tiny fraction is enough to create all observable human diversity.
Why Not Compare Whole DNA? — Repetitive DNA & Satellite DNA
⚡ Why Not Compare Whole DNA?
Comparing entire genomes is:
  • Time-consuming
  • Expensive
  • Unnecessary
Instead, scientists compare specific variable regions.
👉 These regions are highly different between individuals.
🧬 Repetitive DNA — The Target Region
DNA fingerprinting focuses on Repetitive DNA sequences — short DNA stretches repeated many times.
Example pattern: ATGC ATGC ATGC ATGC ATGC
These repeats are separated from rest of DNA using density gradient centrifugation.
These small peaks are called: 👉 Satellite DNA
🛰 Satellite DNA Types & Why These Regions Are Used
Classified Based On:
  • Base composition (AT rich / GC rich)
  • Length
  • Repeat number

📌 Important NCERT Concept: These sequences do NOT code proteins but form a major part of the genome. Non-coding ≠ useless — they regulate structure, evolution, and variation.
🧬 Why These Regions Are Used for Identification
Because they show: High Polymorphism
  • Vary greatly among individuals
  • Same pattern exists in every tissue of the same person
So DNA from any tissue works.
🧪 Biological Sources for DNA Testing
This makes forensic identification possible.
Blood
Saliva
Sperm
Skin
Hair follicle
Bone
🧬 What is DNA Polymorphism?
Definition: Genetic variation present in a population.
Origin of Polymorphism
Comes from mutations.
Only germ-line mutations contribute to polymorphism.
📊 Population Criterion
Variation is called polymorphism only if: frequency > 1% in population
Otherwise it is called rare mutation.
Why Non-Coding Regions Show More Variation
Mutations here:
  • Usually harmless
  • Don't affect survival
  • Don't reduce reproduction
So they: ✔ persist ✔ accumulate ✔ spread
This is why fingerprinting targets them.
🧬 Range of Genetic Variation
These variations are crucial for: evolution, natural selection, speciation.
🧬 SNP (Single Nucleotide Polymorphism)
🔹 Definition
SNP stands for Single Nucleotide Polymorphism.
👉 It is a variation at a single base in DNA sequence that is present in a population.
Example:
Only one base differs (C → T) = SNP.
👨‍🔬 Discovery & VNTR — The Most Important Term
Discovery of DNA Fingerprinting
Developed by: Alec Jeffreys
He used: VNTR probes
🔁 VNTR — Variable Number Tandem Repeat
Meaning: Short DNA sequence, repeated head-to-tail, repeat number varies.
It is a short DNA sequence (10–60 base pairs) that is repeated many times in a row.
AGTCAGTCAGTCAGTC
If "AGTC" is 4 bp:
  • Person A → 5 repeats
  • Person B → 12 repeats
  • Person C → 20 repeats
👉 Repeat number differs → DNA length differs.
That difference is the key to identification.

Because copy number differs → fragment length differs → pattern differs.
Where Are VNTRs Found?
  • Located in non-coding DNA
  • Belong to minisatellite DNA
  • Present on many chromosomes
They do not code for proteins, but they show high variation.
Why VNTR Shows High Polymorphism
During DNA replication, repetitive regions can undergo:
  • unequal crossing over
  • replication slippage
This changes repeat number.
Since this often happens in non-coding DNA:
  • it doesn’t affect survival
  • so variation accumulates
  • so population diversity increases
Why VNTR Is Perfect for DNA Fingerprinting
Because:
✔ Repeat number differs between individuals
✔ Fragment length differs after enzyme cutting
✔ Band pattern becomes unique
Only identical twins share same VNTR pattern.
🧬 What does “Probe” mean in molecular biology?

A probe is a short, single-stranded piece of DNA (or RNA) used to detect a specific DNA sequence by binding to it.
In DNA Fingerprinting
VNTR probe binds only to VNTR regions.
Result:
👉 only those fragments become visible as bands.
Without probe → all DNA fragments look same.
🧪 Steps of DNA Fingerprinting (Technique Logic)
This is the most exam-asked sequence.
1
DNA Isolation
Cells broken → DNA extracted
2
Restriction Digestion
Restriction enzymes cut DNA at specific sequences.
3
Gel Electrophoresis
DNA is negatively charged → moves toward positive electrode. Small fragments move faster, large fragments move slower.
4
Blotting (Southern Blotting)
DNA transferred from gel → membrane (nitrocellulose or nylon).
5
Hybridisation
Radioactive VNTR probe added. Probe binds complementary sequences.
6
Autoradiography
X-ray film shows bands where probe binds. 👉 Band pattern = DNA fingerprint
📊 Why Band Pattern is Unique & PCR Revolution
Why Band Pattern is Unique
Because:
  • VNTR repeat number differs
  • Fragment length differs
  • Distribution differs
So pattern becomes: genetically unique barcode

Exception: Identical twins share identical genome → same fingerprint.
⚡ PCR Revolutionised Fingerprinting
Earlier limitation: Needed large DNA sample.
Now, PCR amplification allows:
  • ✔ Single cell analysis
  • ✔ Degraded samples usable
  • ✔ Faster detection
🔬 Applications of DNA Fingerprinting
Forensic Science
Match crime scene DNA with suspect.
Paternity Testing
Child inherits DNA from both parents. Matching pattern confirms parentage.
Population Genetics
Study migration history, ethnic diversity, and evolution patterns.
Evolutionary Biology Insight
Polymorphisms act as raw material for evolution. Natural selection acts on variation → species change.
🧠 Concept Link Map — Big Picture Understanding
DNA Fingerprinting connects to all major areas of biology, making it a central hub chapter concept.
DNA Fingerprinting
Central Hub
Mutation & Inheritance
Molecular Biology
Evolution
Biotechnology
Forensic Science
Population Genetics

So this topic is a central hub chapter concept — mastering DNA Fingerprinting means connecting Mutation, Inheritance, Molecular Biology, Evolution, Biotechnology, Forensic Science, and Population Genetics.
QUESTION PRACTICE
Q.Which is the basis of genetic mapping of the human genome as well as DNA fingerprinting? NEET 2020
  1. Polymorphism in the DNA sequence
  1. Single nucleotide polymorphism
  1. Polymorphism in the hnRNA sequence
  1. Polymorphism in the RNA sequence
Q. PCR and Restriction Fragment Length Polymorphism are the methods for: AIPMT 2012
  1. Study of enzymes
  1. Genetic transformation
  1. DNA sequencing
  1. Genetic fingerprinting
Q.Satellite DNA is important because it: AIPMT 2015
  1. Codes for proteins are needed in the cell cycle.
  1. Shows a high degree of polymorphism in the population and also the same degree of polymorphism in an individual which is inheritable from parents to children.
  1. Does not code for proteins and is the same in all members of the population.
  1. Codes for enzymes needed for DNA replication.
Q.VNTR belongs to which category of DNA?
A. Euchromatin
B. Minisatellite
C. Microsatellite
D. Heterochromatin
Q.Which scientist developed DNA fingerprinting technique?
A. Watson
B. Mullis
C. Jeffreys
D. Meselson
Q.VNTR polymorphism arises mainly due to variation in:
A. sequence composition
B. base pairing
C. number of repeats
D. nitrogenous bases
Q.The probe used in DNA fingerprinting is:
A. protein fragment
B. single-stranded nucleic acid
C. double-stranded RNA
D. enzyme
Q.Polymorphism is more frequent in non-coding DNA because:
A. mutation rate higher
B. repair mechanism absent
C. mutations there usually harmless
D. replication slower
Q.In DNA fingerprinting, separated DNA fragments are transferred onto membrane by:
A. PCR
B. Western blotting
C. Southern blotting
D. Northern blotting
Q.Assertion: DNA fingerprinting can be done using hair follicles.
Reason: DNA polymorphism pattern is same in all tissues of an individual.
A. Both true, reason correct explanation
B. Both true, but reason not explanation
C. Assertion true, reason false
D. Both false
Q.Which statement is correct?
  1. Satellite DNA codes for proteins
  1. VNTR size ranges from 0.1–20 kb
  1. Polymorphism arises due to mutations
  1. All mutations are polymorphisms
A. 1 & 4
B. 2 & 3
C. 1,2,3
D. 2,3,4
QDNA fingerprinting is least useful in identifying:
A. blood stain source
B. father of child
C. identical twins
D. criminal suspect
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