1. DO NOW Please hand in your outlines Then Answer:
How would you isolate DNA found at a crime scene to analyze? 1

2. Biotech Lab #4: DNA Profiling and Gel Electrophoresis2

3. What is DNA Profiling? A technique used by scientists
to distinguish between individuals
of the same species using only
samples of their DNA 3

4. Stages of DNA Profiling
If only a small amount of DNA is available it can be amplified using the polymerase chain reaction (PCR)
Cells are broken down to release DNA 4

5. The DNA is cut into fragments using restriction enzymes.
Step 2:
The DNA is cut into fragments using restriction enzymes.
Each restriction enzyme cuts DNA at a specific restriction sites that can be in different locations 5

6. 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). 6

8. Stage 3:
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. 8

9. Do Now
Gel electrophoresis has runs from a negative end to a positive end. Why do you think this is?

10. Gel Electrophoresis
A laboratory method used to separate mixtures of DNA, RNA, or proteins according to molecular size. The molecules to be separated are pushed by an electric field through a gel that contains small pores.

11. If the molecule is circular, enzymes are used to cut the DNA
Needs a DNA sample:
Plasmid, PCR product, segment of a chromosome, etc.
If the molecule is circular, enzymes are used to cut the DNA
needs to be linear for the gel
Whatever sample you use, it must be mixed with a loading buffer
contains glycerol and dyes

12. How does Gel Electrophoresis work?
Gel is prepared which will act as a support for support for separation of the fragments of DNA.
The gel is a jello-like material, usually agarose, a substance derived from seaweed.
Holes (a.k.a Wells) are created in the gel. These will serve as a reservoir to hold DNA

13. DNA solutions (Mixtures of different sizes of DNA fragments) are loaded in a well in the gel.

14. Where does the DNA move?
DNA is negatively charged because of the phosphate in the backbone so it is attracted to the positive end of the gel.
The shorter DNA fragments move faster and further than the longer fragments.

15. How can we determine the fragment size of DNA?
Molecular weight markers are often electrophoresed with DNAs
Molecular weight markers are usually a mixture of DNAs with known molecular weights.
Molecular weight markers are used to estimate the sizes of DNA fragments in your DNA sample.

16. Inserts itself between the base pairs.
Ethidium Bromide
An agent commonly used as a nucleic acid stain in molecular biology laboratories
Inserts itself between the base pairs.

18. Stage 4:
The pattern of fragment distribution is then analyzed. 18

19. Video!

20. Use of DNA Profiling DNA profiling is used for: Solving crimes
Medical questions
medical issues 20

21. 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

22. Biological materials used for DNA profiling
Blood
Hair
Saliva
Semen
Body tissue cells 22

23. 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 (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. 23

24. 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: 24

25. Was the suspect at the crime scene?
Suspects Profile
Blood sample from crime scene
Victims profile 25

26. Solving Medical Problems
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 26

27. 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. 27

28. Is this man the father of the child?
Mother
Child
Man 28

29. Famous Cases
Steven Avery was falsely convicted for a crime he did not commit and was in jail for 18 years
DNA evidence showed that he was not guilty
He was convicted a second time and apparently no DNA from him has been found on the crime scene 29

30. 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. 30

31. Do Now- Lab Day! Take a few minutes to review:
What is Gel electrophoresis?
How does it work?
What is the purpose of it? 31

32. Paper Model Of a Gel
At the end of this lab, you will have a paper model of a gel that contains three digested DNA samples. You must properly place the different fragments for each enzyme in the proper location on the gel. Once you have had your gel checked, your teacher will give you another task: add the marker. 32