DNA Fingerprinting DNA Profilingpowerpoint
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Transcript of DNA Fingerprinting DNA Profilingpowerpoint
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DNA Profiling(DNA fingerprinting)
A method of Forensicidentification
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What is DNA Profiling?
A technique used by scientists todistinguish between individuals ofthe same species using only samples
of their DNA
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Who Invented it?
The process ofDNA fingerprintingwas invented by
Alec Jeffreys at theUniversity ofLeicester in 1985.
He was knighted in1994.
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How do you figure out that
someones DNA is more similar to
anothers?
The primary method of assessingsimilarities is by use of DNAfingerprinting or DNA restriction
analysis.
This process makes use of specialproteins called restriction enzymes
and sections of the chromosomecalled tandem repeats
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Tandem Repeats
A region of the chromosome thatcontains multiple copies of a coreDNA sequence that are arranged in a
repeating fashion
Repeats act as fillers or spacersbetween coded sections of DNA
All humans have the same type ofrepeats but there is tremendousvariation in the number of repeats
that each of us has.
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Stages of DNA Profiling
Stage 1:
Cells are broken down
to release DNA
If only a small amountof DNA is available itcan be amplified using
the polymerase chainreaction (PCR)
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Stages of DNA Profiling
Step 2:The DNA is cut into fragments using restriction
enzymes.
Each restriction enzyme cuts DNA at a specific basesequence.
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SSR= Simple sequence Repeatsor
SSLP= Simple sequence length
polymorphism
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d
D
Probe binds repetitive
sequences
The number of repeated units in a tandem array is variable. Individuals
heterozygous for different numbers of tandem repeats can be detected,
and the heterozygous site (s) used as a marker (s) for mapping.
This VNTR locus will form two bands on a Southern blot: one long and
one short. Similar to an RFLP locus, this heterozygous site can be used
for genetic mapping.
At present, VNTR analysis is rapidly performed using PCR.
Restriction target sites are outside the repetitive array.
The basic unit of the array is indicated by the arrows.
Simple-Sequence Length Polymorphisms (SSLPs)
VNTRs :Variation in the
Number of
Tandem Repeats
or Mini-satellite
Molecular Markers
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Restriction Fragment Length
Polymorphisms (RFLP)
RFLPs are different fragment lengthsof base pairs that result from cuttinga DNA molecule with a restriction
enzyme
It is the length differences associatedwith DNA strands or RFLPs that allow
one to distinguish one person fromanother.
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Stages of DNA Profiling
The sections of DNA that are cut outare called restriction fragments.
This yields thousands of restrictionfragments of all different sizesbecause the base sequences beingcut may be far apart (long fragment)or close together (short fragment).
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Stages of DNA Profiling
Stage 3:
Fragments areseparated on the
basis of size usinga process called gelelectrophoresis.
DNA fragments are
injected into wellsand an electriccurrent is appliedalong the gel.
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Stages of DNA Profiling
DNA is negativelycharged so it isattracted to thepositive end of thegel.
The shorter DNAfragments movefaster than thelonger fragments.
DNA is separated onbasis of size.
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Stages of DNA Profiling
A radioactivematerial is addedwhich combines
with the DNAfragments toproduce afluorescent image.
A photographiccopy of the DNAbands is obtained.
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Stages of DNA Profiling
Stage 4:
The pattern of fragment distributionis then analysed.
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Uses of DNA Profiling
DNA profiling isused to solvecrimes and
medicalproblems
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Crime
Forensic science is the use ofscientific knowledge in legalsituations.
The DNA profile of each individual ishighly specific.
The chances of two people having
exactly the same DNA profile is30,000 million to 1 (except foridentical twins).
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Biological materials used for DNA
profiling Blood
Hair
Saliva
Semen
Body tissue cells
DNA samples havebeen obtained fromvaginal cells
transferred to theoutside of a condomduring sexualintercourse.
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DNA Profiling can solve crimes
The pattern of the DNA profile is thencompared with those of the victim and thesuspect.
If the profile matches the suspect itprovides strong evidence that the suspectwas present at the crime scene (NB:itdoes not prove they committed thecrime).
If the profile doesnt match the suspectthen that suspect may be eliminated fromthe enquiry.
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Example
A violent murder occurred.
The forensics team retrieved a bloodsample from the crime scene.
They prepared DNA profiles of theblood sample, the victim and asuspect as follows:
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Was the suspect at the crime
scene?
SuspectsProfile
Blood samplefrom crimescene
Victimsprofile
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Solving Medical Problems
DNA profiles can be used to determinewhether a particular person is the parentof a child.
A childs paternity (father) andmaternity(mother) can be determined.
This information can be used in
Paternity suits Inheritance cases
Immigration cases
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Example: A Paternity Test
By comparing the DNA profile of a
mother and her child it is possible to
identify DNA fragments in the childwhich are absent from the mother and
must therefore have been inherited
from the biological father.
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Is this man the father of the child?
Mother Child Man
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An Example Using EcoR I for a
Question of Paternity
EcoR I cuts asimilar section of
DNA on Bob,Larry, and Mary
After the cut how
many fragmentsBob, Larry, andMary have?
Answer: 2, 3, and
none
Recall: EcoR I cuts only at GAATTC
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Example Cont
After the DNA is cut with EcoR I, Bobs,Larrys and Marys fragments are placed indifferent lanes on an agarose gel
The fragments are then subjected to anelectric field
The smaller fragments move faster, thelarger ones move slower
This process of separating the fragmentsby length is called electrophoresis.
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Resulting Picture after
Electrophoresis
The biggerfragments arenear the top
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Paternity Test
In general the
childs DNA mustbe a combinationof Marys DNA and
one of the men.Which man is thefather?
Answer: Larry
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Famous cases
In 2002 ElizabethHurley used DNAprofiling to prove
that Steve Bingwas the father
of her child Damien
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Famous Cases
Colin Pitchfork wasthe first criminalcaught based on
DNA fingerprintingevidence.
He was arrested in1986 for the rape
and murder of twogirls and wassentenced in 1988.
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Famous Cases
O.J. Simpson wascleared of a doublemurder charge in1994 which relied
heavily on DNAevidence.
This casehighlighted labdifficulties.
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