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DNA Fingerprinting
Content
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The structure of DNA
History of DNA fingerprinting
DNA Electrophoresis
DNA fingerprinting application
The structure of DNA
• The characteristics of all living
organisms, including humans, are
essentially determined by
information contained within DNA
that they inherit from their parents.
The molecular structure of DNA can
be imagined as a zipper with each
tooth represented by one of four
letters (A, C, G, or T), and with
opposite teeth forming one of two
pairs, either A-T or G-C.
• The letters A, C, G, and T
stand for adenine, cytosine,
guanine, and thymine, the
basic building blocks of
DNA.
• The information contained in
DNA is determined
primarily by the sequence of
letters along the zipper. For
example, the sequence
ACGCT represents different
information than the
sequence AGTCC in the
same way that the word
"POST" has a different
meaning from "STOP" or
"POTS," even though they
use the same letters. The
traits of a human being are
the result of information
contained in the DNA code.
• Living organisms that
look different or have
different
characteristics also
have different DNA
sequences. The more
varied the organisms,
the more varied the
DNA sequences. DNA
fingerprinting is a very
quick way to compare
the DNA sequences of
any two living
organisms.
History
• DNA fingerprinting was developed in 1984
by Alec. J. Jeffrey at the University of
Leicester while he was studying the gene
for myoglobin
• He found that myoglobin genes contain
many segments that vary in size and
composition and have no apparent functions
• Jeffrey called these segments minisatellites
because they were small and surrounding
the part of the gene.
• In 1987, British baker Colin Pitchfork was
the first criminal caught using DNA
fingerprinting
• 1990 California establishes DNA fingerprint
banks for sex offenders.
DNA Electrophoresis
Experiment
• Electrophoresis is a
technique that can be
used to separate the
DNA and RNA
fragments from one
another according to
their sizes.
• It can be done by loading the fragments(碎片) in a
well at one end of a piece of gel,which is
immersed in a buffer solution inside a gel tray.
• An electrical current is then passed through the gel.
Diagram showing gel electrophoresis
• As DNA or RNA molecules
contain many phosphate
groups,they are highly
negatively charged.The
fragments are attracted towards
the positively charged electrode.
• The fragements pass through a
gel at a rate that is inversely
proportional to their size.Small
fragments move faster than
large fragments through the
gel.In other words,they travel
further through the gel.This
procedure can be used to
separate different DNA or RNA
fragments into bands
• These bands can be
visualized by staining the
gel with ethidium
bromide.It is a dye that
intercalates between the
nitrogenous bases and
gives a pinkish orange
colour under UV
light.Usually a marker is
loaded together with the
sample that contains bands
with known sizes.In this
way,the sizes of unknown
fragments can be
estimated.
• The DNA sequences
of DNA fragments can
be known by means of
an automated DNA
sequencing machine.
DNA sequencing result
Home Made Gel for
Electrophoresis
Procedure of DNA
fingerprinting
1: Isolation of DNA.
DNA must be recovered from the cells or tissues of
the body. Only a small amount of tissue - like blood,
hair, or skin - is needed. For example, the amount of
DNA found at the root of one hair is usually
sufficient.
2: Cutting, sizing, and sorting.
Special enzymes called restriction enzymes are used
to cut the DNA at specific places. For example, an
enzyme called EcoR1, found in bacteria, will cut
DNA only when the sequence GAATTC occurs. The
DNA pieces are sorted according to size by a sieving
technique called electrophoresis. The DNA pieces
are passed through a gel made from seaweed agarose
(a jelly-like product made from seaweed). This
technique is the biotechnology equivalent of
screening sand through progressively finer mesh
screens to determine particle sizes.
3: Transfer of DNA to nylon.
The distribution of DNA pieces is
transferred to a nylon sheet by
placing the sheet on the gel and
soaking them overnight.
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.
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
DNA fingerprinting application
• parentage test
• Forensic science
• DNA ID Card
Uses in parentage test
• DNA fingerprinting is
widely used in
parentage testing
around the world. By
comparing different
DNA sequences, we
can analyse the
relationship between
any two individuals.
• The test will be
conducted using the
latest in PCR
(Polymerase Chain
Reaction) technology.
The PCR method is the
most widely used and
trusted DNA testing
technology today.
• Polymerase chain reaction
(PCR) is a molecular
biology technique for
enzymatically replicating
DNA without using a
living organism. Like
amplification using living
organisms, the technique
allows a small amount of
the DNA molecule to be
amplified exponentially.
• The results that you
receive will look like a
table full of numbers.
There are three columns:
one for the Mother, one
for the Child and one
for the possible Father.
Each row in the table
represents a different
DNA locus, which
represent that specific
area on their individual
DNA .
Uses in forensics
• Because human DNA is
unique to individuals,
DNA isolated from blood,
hair, skin cell, or other
genetic evidence left at
the scene of crime can be
compared, using the
DNA fingerprinting
technology, with the
DNA of a criminal
suspect to determine
guilt or innocence.
• In criminal cases, this
generally involves
obtaining samples from
crime-scene evidence
and a suspect, extracting
the DNA, and analyzing
it for the presence of a
set of specific DNA
regions (markers).
• Scientists find the
markers in a DNA
sample by designing
small pieces of DNA
(probes) that will each
seek out and bind to a
complementary DNA
sequence in the sample.
• Forensic scientists
compare these DNA
profiles to determine
whether the suspect's
sample matches the
evidence sample. If the
sample profiles don't
match, the person did
not contribute the DNA
at the crime scene.
DNA ID Card
• The DNA ID Card
contains your personal
information and DNA
profile. The
information recorded
on the card includes
photograph, Name,
Gender, Date of Birth
and DNA personal
profile.