DNA profiling is a technique used by scientists to distinguish between individuals using DNA samples. It was invented in 1985 by Alec Jeffreys at the University of Leicester. The process involves breaking down cells to extract DNA, cutting the DNA into fragments using restriction enzymes, separating the fragments by size using gel electrophoresis, and comparing the pattern to DNA from other individuals. DNA profiling can help solve crimes by matching DNA from a crime scene to a suspect, and solve medical problems by determining biological relationships in cases of paternity, maternity or inheritance disputes. It has been used successfully in many famous court cases over the years.

1. DNA ProfilingDNA Profiling
(DNA fingerprinting)(DNA fingerprinting)

2. What is DNA Profiling?What is DNA Profiling?
A technique used by scientists toA technique used by scientists to
distinguish between individuals ofdistinguish between individuals of
the same species using only samplesthe same species using only samples
of their DNAof their DNA

3. Who Invented it?Who Invented it?
 The process of DNAThe process of DNA
fingerprinting wasfingerprinting was
invented by Alecinvented by Alec
Jeffreys at theJeffreys at the
University ofUniversity of
Leicester in 1985.Leicester in 1985.
 He was knighted inHe was knighted in
1994.1994.

4. Stages of DNA ProfilingStages of DNA Profiling
 Stage 1Stage 1::
Cells are broken downCells are broken down
to release DNAto release DNA
If only a small amountIf only a small amount
of DNA is available itof DNA is available it
can be amplified usingcan be amplified using
the polymerase chainthe polymerase chain
reaction (PCR)reaction (PCR)

5. Stages of DNA ProfilingStages of DNA Profiling
 Step 2:Step 2:
The DNA is cut into fragments usingThe DNA is cut into fragments using restrictionrestriction
enzymesenzymes..
Each restriction enzyme cuts DNA at a specific baseEach restriction enzyme cuts DNA at a specific base
sequence.sequence.

6. Stages of DNA ProfilingStages of DNA Profiling
 The sections of DNA that are cut outThe sections of DNA that are cut out
are calledare called restriction fragments.restriction fragments.
 This yields thousands of restrictionThis yields thousands of restriction
fragments of all different sizesfragments of all different sizes
because the base sequences beingbecause the base sequences being
cut may be far apart (long fragment)cut may be far apart (long fragment)
or close together (short fragment).or close together (short fragment).

7. Stages of DNA ProfilingStages of DNA Profiling
Stage 3:Stage 3:
 Fragments areFragments are
separated on theseparated on the
basis of size usingbasis of size using
a process calleda process called gelgel
electrophoresis.electrophoresis.
 DNA fragments areDNA fragments are
injected into wellsinjected into wells
and an electricand an electric
current is appliedcurrent is applied
along the gel.along the gel.

8. Stages of DNA ProfilingStages of DNA Profiling
DNA is negativelyDNA is negatively
charged so it ischarged so it is
attracted to theattracted to the
positive end of thepositive end of the
gel.gel.
The shorter DNAThe shorter DNA
fragments movefragments move
faster than thefaster than the
longer fragments.longer fragments.
DNA is separated onDNA is separated on
basis of size.basis of size.

9. Stages of DNA ProfilingStages of DNA Profiling
 A radioactiveA radioactive
material is addedmaterial is added
which combineswhich combines
with the DNAwith the DNA
fragments tofragments to
produce aproduce a
fluorescent image.fluorescent image.
 A photographicA photographic
copy of the DNAcopy of the DNA
bands is obtained.bands is obtained.

10. Stages of DNA ProfilingStages of DNA Profiling
Stage 4:Stage 4:
 The pattern of fragment distributionThe pattern of fragment distribution
is then analysed.is then analysed.

11. Uses of DNA ProfilingUses of DNA Profiling
 DNA profiling isDNA profiling is
used to solveused to solve
crimescrimes andand
medicalmedical
problemsproblems

12. CrimeCrime
 Forensic science is the use ofForensic science is the use of
scientific knowledge in legalscientific knowledge in legal
situations.situations.
 The DNA profile of each individual isThe DNA profile of each individual is
highly specific.highly specific.
 The chances of two people havingThe chances of two people having
exactlyexactly the same DNA profile isthe same DNA profile is
30,000 million to 1 (except for30,000 million to 1 (except for
identical twins).identical twins).

13. Biological materials used for DNABiological materials used for DNA
profilingprofiling
 BloodBlood
 HairHair
 SalivaSaliva
 SemenSemen
 Body tissue cellsBody tissue cells
 DNA samples haveDNA samples have
been obtained frombeen obtained from
vaginal cellsvaginal cells
transferred to thetransferred to the
outside of a condomoutside of a condom
during sexualduring sexual
intercourse.intercourse.

14. DNA Profiling can solve crimesDNA Profiling can solve crimes
 The pattern of the DNA profile is thenThe pattern of the DNA profile is then
compared with those of the victim and thecompared with those of the victim and the
suspect.suspect.
 If the profileIf the profile matchesmatches the suspect itthe suspect it
provides strong evidence that the suspectprovides strong evidence that the suspect
was present at the crime scene (was present at the crime scene (NB:itNB:it
does not prove they committed thedoes not prove they committed the
crime).crime).
 If the profileIf the profile doesn’tdoesn’t match the suspectmatch the suspect
then that suspect may be eliminated fromthen that suspect may be eliminated from
the enquiry.the enquiry.

15. ExampleExample
 A violent murder occurred.A violent murder occurred.
 The forensics team retrieved a bloodThe forensics team retrieved a blood
sample from the crime scene.sample from the crime scene.
 They prepared DNA profiles of theThey prepared DNA profiles of the
blood sample, the victim and ablood sample, the victim and a
suspect as follows:suspect as follows:

16. Was the suspect at the crimeWas the suspect at the crime
scene?scene?
Suspects
Profile
Blood sample
from crime
scene
Victims
profile

17. Solving Medical ProblemsSolving Medical Problems
DNA profiles can be used to determineDNA profiles can be used to determine
whether a particular person is the parentwhether a particular person is the parent
of a child.of a child.
A childs paternity (father) andA childs paternity (father) and
maternity(mother) can be determined.maternity(mother) can be determined.
This information can be used inThis information can be used in
• Paternity suitsPaternity suits
• Inheritance casesInheritance cases
• Immigration casesImmigration cases

18. Example: A Paternity TestExample: A Paternity Test
 By comparing the DNA profile of aBy comparing the DNA profile of a
mother and her child it is possible tomother and her child it is possible to
identify DNA fragments in the childidentify DNA fragments in the child
which are absent from the mother andwhich are absent from the mother and
must therefore have been inheritedmust therefore have been inherited
from the biological father.from the biological father.

19. Is this man the father of the child?Is this man the father of the child?
Mother Child Man

20. Famous casesFamous cases
 In 2002 ElizabethIn 2002 Elizabeth
Hurley used DNAHurley used DNA
profiling to proveprofiling to prove
that Steve Bingthat Steve Bing
was the fatherwas the father
of her child Damienof her child Damien

21. Famous CasesFamous Cases
 Colin Pitchfork wasColin Pitchfork was
the first criminalthe first criminal
caught based oncaught based on
DNA fingerprintingDNA fingerprinting
evidence.evidence.
 He was arrested inHe was arrested in
1986 for the rape1986 for the rape
and murder of twoand murder of two
girls and wasgirls and was
sentenced in 1988.sentenced in 1988.

22. Famous CasesFamous Cases
 O.J. Simpson wasO.J. Simpson was
cleared of a doublecleared of a double
murder charge inmurder charge in
1994 which relied1994 which relied
heavily on DNAheavily on DNA
evidence.evidence.
 This caseThis case
highlighted labhighlighted lab
difficulties.difficulties.

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