Dna Finger Printing

SEMINAR
DNA Fingerprinting
 Definition
 History
 How it works
 Different Methods of processing
 Application’s
 Draw Backs
 References
DEFINITION
Forensic science: Intersection of Law and Science
DNA fingerprinting: Analysis of an organism’s

unique DNA composition as a characteristic
marker.
A technique used by scientists to distinguish

between individuals of the same species using only
samples of their DNA.
HISTORY
•1985: United Kingdom

•The process of DNA
fingerprinting was invented
by-
•Sir Alec Jeffreys
•Dr. peter Gill
•Dr. Dave Werrett at the
University of Leicester in
1985.
• Chemical Structure of DNA is always the same.
• Important: The order of the base pairs is different!
• 3 Billion Nucleotides form our 46 chromosomes.
• In fact, no two people on Earth have exactly the same
genetic sequence, except identical twins.
• Important: Every cell contains a copy of our DNA!
How does it Work?
• DNA Fingerprinting using VNTR's
• VNTR(variable number of tandem repeats)- recognition

that variable numbers of repeated nucleotides can be
found in DNA and can be used for identification of
individuals.
• VNTR’s provide a scientific marker for identity.
• Cut out the segment of the chromosome containing this

variable number of tandem repeats (VNTR's ).
• Identify the VNTR's for the DNA sequence of the repeat.
Isolation of DNA
DNA must be recovered from the cells
or tissues of the body.
• Blood
• Hair
• Saliva
• Semen
• DNA samples have been obtained from
vaginal cells transferred to the outside
of a condom during sexual intercourse.
Only a small amount of tissue is
needed. For example, the amount of
DNA found in one drop of blood or in
one hair root is enough.
Stages of DNA Fingerprinting
• Step 1:
Cells are broken down
to release DNA.
If only a small amount of
DNA is available it can be
amplified using the
polymerase chain reaction
(PCR).
RFLP – Restriction Fragment Length Polymorphism
• More accurate than PCR
• Requires a large sample of fresh DNA
• Takes longer time & costly than PCR
• When a match if found, there is no question as to
whether the suspect was at the scene.
PCR – Polymerase Chain Reaction
• Takes less time, less costly
• Requires only a small sample
• That sample is amplified using polymerases to force
the small amounts of DNA to copy themselves many
times.
• Can be performed on older samples
• If no match is found, the donor was not at the scenes
Step 2: Cutting, Sizing, and Sorting
Special restriction enzymes are used to cut the DNA
at specific places.
The DNA pieces are sorted according to size by a
technique called electrophoresis. The DNA pieces are
passed through a gel made from seaweed agarose.
Electrophoresis
DNA fragments are injected into
wells and an electric current is
applied along the gel.
DNA is negatively charged so it is

attracted to the positive end of the gel.
The shorter DNA fragments move faster
than the longer fragments.
DNA is separated on basis of size.
Electrophoresis
Step 3: Transfer of DNA to Nylon
The DNA pieces are transferred to a nylon sheet by
placing the sheet on the gel and soaking them
overnight.
The pattern of fragments

Gel with DNA
pieces from
Nylon Sheet
“blotting up”
are transferred to a nylon
PCR or RFLP the pieces membrane by a process
called Southern blotting.
Steps 4-5: Probing
Adding radioactive or colored probes to the nylon
sheet produces a pattern called the DNA
fingerprint. Each probe typically sticks in only
one or two specific places on the nylon sheet.
Colored Probes X-Ray film is put

Bind to Certain over the Nylon
Sequences in the Sheet so we can
DNA Pieces and View the Results
Stains Them
Step 6: DNA Fingerprint
The final DNA fingerprint is built by using
several probes (5-10 or more) simultaneously.
It resembles the bar codes used by grocery
store scanners.
Police use the fingerprints to compare a
suspect’s DNA to the DNA found at a
crime scene.
Application’s
1. Paternity Test
• By comparing the
DNA profile of a
mother and her child it
is possible to identify
DNA fragments in the
child which are absent
from the mother and
must therefore have
been inherited from the
biological father.
2. DNA Profiling can solve crimes
• The pattern of the DNA profile is

then compared with those of the
victim and the suspect.
• If the profile matches the suspect it
provides strong evidence that the
suspect was present at the crime
scene.
• If the profile doesn’t match the
suspect then that suspect may be
eliminated from the enquiry.
3. Personal Identification
• The notion of using DNA fingerprints as a sort of
genetic bar code to identify individuals has been
discussed.
4.Diagnosis of Inherited Disorders
• Diagnose inherited disorders in both prenatal and new
born babies.
• By studying the DNA fingerprints of relatives who
have a history of some particular disorder.
• Identify DNA patterns associated with the disease.
• These disorders may include hemophilia, Alzheimer's,
sickle cell anemia, thalassemia, and many others.
Famous Cases
• Colin Pitchfork was the first criminal
caught based on DNA fingerprinting
evidence.
• He was arrested in 1986 for the rape and
murder of two girls.
• O.J. Simpson was cleared of a double
murder charge in 1994 which relied
heavily on DNA evidence.
• This case highlighted lab difficulties.
• In 2002 Elizabeth Hurley used DNA

profiling to prove that Steve Bing was
the father of her child Damien.
Drawbacks
•Collecting samples
–High temperatures can degrade DNA
–Bacteria
–Moisture
•Human Error
– Sneezes, improper storage, failure to label samples
•Chain of Custody
–Collection of evidence must be systematically
recorded and access to evidence must be controlled.
References
Russel, P.J. 1998 Genetics (5th edition).
Chawla, H.S.2005 Introduction to Plant Biotechnology(2nd edition)
Singh, B.D. 2005 Biotechnology Expanding Horizons
• Lecture 7: A few famous cases involving DNA Evidence. March 2007

– http://nitro.biosci.arizona.edu/courses/EEB195-2007/Lecture07/Le
cture07.html
• Baden, Michael. DNA Profiling.
– http://www.kathyreichs.com/dnaprofiling.htm
• http://www.biologycorner.com/bio4/notes/DNA_fingerprint.
• http://www.scq.ubc.ca/a-brief-tour-of-dna-fngerprinting/
• http://evolution.berkeley.edu/evolibrary/news/060301_crime

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SEMINAR

Forensic science: Intersection of Law and Science

DNA fingerprinting: Analysis of an organism’s

A technique used by scientists to distinguish

•1985: United Kingdom

• DNA Fingerprinting using VNTR's

• VNTR(variable number of tandem repeats)- recognition

• Cut out the segment of the chromosome containing this

DNA is negatively charged so it is

The pattern of fragments

Colored Probes X-Ray film is put

• The pattern of the DNA profile is

• In 2002 Elizabeth Hurley used DNA

• Lecture 7: A few famous cases involving DNA Evidence. March 2007

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