Transcript Genetic fingerprinting

Genetic fingerprinting
Each DNA profile is unique!
Learning Objectives:
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What is genetic fingerprinting?
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How is genetic fingerprinting carried out?
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How are the results interpreted?
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For what purposes is it used?
What is Genetic fingerprinting?
A technique used by scientists which is based
on the fact that DNA of every individual,
except identical twins, is unique.
It is also known as DNA fingerprinting or DNA
profiling.
Genetic fingerprinting
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Regions of
chromosomes that code
for proteins are called
exons.
Other regions that are
non-coding are called
introns.
95% of Human DNA
does not code for any
characteristics
Genetic fingerprinting
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Introns contain blocks of
repeated nucleotides called
core sequences.
It is the number of times
that these core sequences
are repeated that produces
the variations in
individuals.
The more closely related
two individuals are the
more similar the core
sequences will be.
Genetic fingerprinting
How it is done?
Stage 1:

DNA is extracted from a sample
(blood, hair, semen, skin).
If only a small amount of DNA
is available it can be amplified
using the polymerase chain
reaction (PCR).
OR
Cells are broken down to release
DNA.
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The DNA is cut into millions of
small fragments using restriction
endonucleases.
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The restriction endonucleases
are chosen for their ability to cut
close to but not within the core
sequences.
How it is done?
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The sections of DNA that are cut out are
called restriction fragments.
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This yields thousands of restriction fragments
of all different sizes because the base
sequences being cut may be far apart (long
fragment) or close together (short fragment).
How is it done?
Stage 2:
 Fragments are separated on
the basis of size using a
process called gel
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.
How it is done?
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The smaller the
fragment – the faster it
moves.
DNA is separated into
bands according to size
of the fragments.
How it is done?
Stage 3:
 The gel is immersed in alkali in order to separate the double
strands into single strands.
 The pattern of fragments are transferred to a nylon membrane
by a process called Southern blotting.
Southern Blotting
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A thin nylon membrane is laid over the gel.
The membrane is covered with several sheets of
absorbent paper, which draw up the liquid
containing the DNA by capillary action.
This transfers the DNA fragments to the nylon
membrane in precisely the same relative positions
they occupied on the gel.
The DNA fragments are then fixed to the membrane
using UV light.
How it is done?
Stage 4:
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Radioactive probes are used to attach to the core sequences
(hybridisation).
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The probes have base sequences which are complementary to the core
sequences.
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Any probes not bound are washed off.
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The membrane is dried.
How it is done?
Stage 5:
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The nylon sheet is placed under
X-ray film.
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The radioactive probes on the
DNA fragments expose the film.
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This produces visible pattern of
light and dark bands which is
unique to each individual.
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The pattern of fragment
distribution is then analysed.
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The pattern of the bands is
unique to every individual
(except identical twins).
Uses of genetic fingerprinting
Stage 6:
 The results can then be
analysed and interpreted.
 Genetic fingerprinting is
used to solve crimes and
medical problems.
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The DNA profile of each
individual is highly specific.
The chances of two people
having exactly the same DNA
profile is 30,000 million to 1
(except for identical twins).
Genetic fingerprinting can solve crimes
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The pattern of the DNA profile is 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 (NB: it does not prove they committed the
crime).
If the profile doesn’t match the suspect then that
suspect may be eliminated from the enquiry.
Solving Medical Problems
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DNA profiles can be used to determine whether a
particular person is the parent of a child.
A child’s paternity (father) and maternity (mother)
can be determined.
This information can be used in
Paternity suits
Inheritance cases
Immigration cases
Example: A 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.
Mother
Child
Man
Genetic variability within a population
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A population whose members have very
similar genetic fingerprints has little genetic
diversity.
A population whose members have a greater
variety of genetic fingerprints has greater
genetic diversity.
Tasks
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Complete the cut and stick activity.
A2 Biology pg 278-279 – Answer the
application questions.