1. DNA Profiling
(DNA fingerprinting)

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

3. Who Invented it?
The process of DNA fingerprinting was invented by Alec Jeffreys at the University of Leicester in 1985.
He was knighted in 1994.

4. Stages of DNA Profiling
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)

5. Polymerase Chain Reaction (PCR)
PCR is a means to amplify a particular piece of DNA
Amplify= making numerous copies of a segment of DNA
PCR can make billions of copies of a target sequence of DNA in a few hours
PCR was invented in the 1984 as a way to make numerous copies of DNA fragments in the laboratory
Its applications are vast and PCR is now an integral part of Molecular Biology

6. DNA Replication vs. PCR
PCR is a laboratory version of DNA Replication in cells
The laboratory version is commonly called “in vitro” since it occurs in a test tube while “in vivo” signifies occurring in a living cell.

7. PCR
The DNA, DNA polymerase, buffer, nucleoside triphosphates, and primers are placed in a thin-walled tube and then these tubes are placed in the PCR thermal cycler
PCR Thermocycler

8. The next cycle will begin by denaturing the new DNA strands formed in the previous cycle

9. PCR has become a very powerful tool in molecular biology
One can start with a single sperm cell or stand of hair and amplify the DNA sufficiently to allow for DNA analysis and a distinctive band on an agarose gel.
One can amplify fragments of interest in an organism’s DNA by choosing the right primers.
One can use the selectivity of the primers to identify the likelihood of an individual carrying a particular allele of a gene.

10. Stages of DNA Profiling
Step 2:
The DNA is cut into fragments using restriction enzymes.
Each restriction enzyme cuts DNA at a specific base sequence.

11. Stages of DNA Profiling
The sections of DNA that are cut out are called restriction fragments.
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).

12. Stages of DNA Profiling
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.

13. Gel electrophoresis DNA extract added well gelatinous sheet solution
The solution is a ‘buffer solution’ which stops the gel from drying out but does not affect the separation process
solution

14. Stages of DNA Profiling
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.

15. + Gel electrophoresis DNA samples placed in wells cut in gel
thin slab of
gel
Voltage supply
negative electrode
DNA fragments
Move from negative
To positive
positive
electrode +

16. Stages of DNA Profiling
A radioactive material is added which combines with the DNA fragments to produce a fluorescent image.
A photographic copy of the DNA bands is obtained.

17. Appearance of separated fragments on gel
These bands will
contain the shorter
DNA fragments
I am grateful to Professor E.J. Wood and Denise Ashworth for permission to reproduce this image of DNA gel electrophoresis
This account is necessarily greatly simplified. In fact the DNA fragments which are separated by electrophoresis are colourless and have to be revealed by special treatments.
There may be hundreds of fragments separated in the gel. To reveal the fragments of particular interest, a nylon membrane is applied to the gel sheet and the DNA fragments transfer to this. The double-stranded DNA is then separated into single strands by heating.
A radioactive probe is applied. The probe is a short length of DNA complementary to the fragments that are of interest
The ‘probe’ binds to the corresponding section of DNA on the nylon membrane which is then placed on an X-ray film. When the film is developed, the radioactive bands show up..
These bands will contain the longer DNA fragments
© Prof. E.J.Wood
© Prof. E. Wood
starting positions
Appearance of bands

18. Stages of DNA Profiling
The pattern of fragment distribution is then analysed.

19. Uses of DNA Profiling
DNA profiling is used to solve crimes and medical problems

20. Crime
Forensic science is the use of scientific knowledge in legal situations.
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).

21. Chances of a match Suppose that…………
….there is a chance of 1 in 10 that this
fragment occurs in many individuals…
…and.there is a chance of 1 in 20 that this
fragment occurs in many individuals…
…and.there is a chance of 1 in 10 that this
fragment occurs in many individuals…
…and.there is a chance of 1 in 30 that this
fragment occurs in many individuals, but…

22. Probability of a match
…the probability of all 4 bands matching in any person other than
the suspect is
1 in x 1 in x 1 in x 1 in 30
= 1 in 10 x 20 x 10 x 30 That is 1 in 60,000
When a larger number of bands is involved, the probability that
the suspect is not guilty becomes one in many thousands*
*or millions!
*Or, in some cases, millions.

23. Biological materials used for DNA profiling
Blood
Hair
Saliva
Semen
Body tissue cells
Skin cells
Nails
Etc.

24. 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 (NOTE: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.

25. Example A violent murder occurred.
The forensics team retrieved a blood sample from the crime scene.
They prepared DNA profiles of the blood sample, the victim and a suspect as follows:

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

27. Solving Medical Problems
DNA profiles can be used to determine whether a particular person is the parent of a child.
A childs paternity (father) and maternity(mother) can be determined.
This information can be used in
Paternity suits
Inheritance cases
Immigration cases

28. 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.

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

30. Famous cases
In 2002 Elizabeth Hurley used DNA profiling to prove that Steve Bing was the father
of her child Damien

31. 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 and was sentenced in 1988.

32. Famous Cases
O.J. Simpson was cleared of a double murder charge in 1994 which relied heavily on DNA evidence.
This case highlighted lab difficulties.

33. Next Week! We will read about:
Tears of the cheetah : and other tales from the genetic frontlines / Stephen J. O'Brien
"In Tears of the Cheetah, medical geneticist and conservationist Stephen J. O'Brien narrates fast-moving science adventure stories that explore the mysteries of survival among the earth's most endangered and beloved wildlife. Here we uncover the secret histories of exotic species such as Indonesian orangutans, humpback whales, and the imperiled cheetah - the world's fastest animal, which nonetheless cannot escape its own genetic weaknesses." "Among these genetic detective stories we also discover how the Serengeti lions have lived with FIV (the feline version of HIV), where giant pandas really come from, how bold genetic action pulled the Florida panther from the edge of extinction, how the survivors of the medieval Black Death passed on a genetic gift to their descendents, and how mapping the genome of the domestic cat helped solve a murder case in Canada."--BOOK JACKET.