1. What happens now that the DNA has been extracted?
Gel Electrophoresis
An electrical current is applied to a gel matrix which contains samples of DNA. The electric current causes the protein or nucleic acid molecules to move through the gel, allowing for the separation of molecules of different sizes.

2. How does gel electrophoresis work?
Place a block of gel (agarose) in a small holding tank. The gel is solid at room temperature and has a neutral charge.
The small holding tank is filled with a buffer solution. This solution resists changes in pH to protect sensitive equipment.

3. How does gel electrophoresis work?
3. Small wells at the end of the gel block are filled with an experimental sample of DNA and a control that are mixed with dye.
4. An electric current is applied to the small holding tank that causes the DNA samples to propel through the gel.(Small molecules travel faster than larger molecules)

4. How does gel electrophoresis work?
5. The electric current is removed when the colored dye reaches the other end.
6. The gel is stained with a solution that enhances the color of the dye.
7. The gel is “read” by measuring how far each molecule traveled during the time allowed.

6. How it works

7. Reading The Results

8. Reading The Results

9. Reading The Results Suspect A Suspect C Control Suspect B
Crime scene sample
Reading The Results

10. Crime scene sample
Control
Control S1 S2
Reading The Results

11. What can gel electrophoresis be used for?
DNA Fingerprinting (forensics)
Determining paternity
Searching for a genetic marker for a particular disease.

12. So lets review…………… What is the function of each of the following:
Agarose Gel
Electric Current
“Wells” in the gel

13. So lets review……………
Toward which pole (+ or -) does DNA migrate when the electric current is run through the gel?
Why do DNA molecules move toward this pole?

14. So lets review……………
Describe how different sized DNA fragments are separated by the gel matrix.

15. So lets review……………
What do the bands in the drawing of the agarose gel represent?
Which band(s) traveled slowest?
Which band(s) traveled fastest?
Where would the positive and negative ends of the gel be in the diagram to the right?
How many bands are shared in common by all of the individuals?
Are there any bands which are unique to only one individual? ____ If so, which one?