1. DNA ELECTROPHORESIS OR
DNA FINGERPRINTING

2. FORENSICS BACKGROUND
During the investigation of violent crimes such as a homicide, fingerprints are not the most common type of evidence recovered.
Hair and blood are more likely to be the focus of these investigations.
Dr. Ray White (1980) developed the technique for “DNA fingerprinting” which was first admitted as evidence to convict someone in 1987.

3. OVERVIEW OF DNA FINGERPRINTING
DNA from cells found at a crime scene and from suspects is collected and cut with restriction enzymes
restriction enzymes seek out specific DNA base pair (bp) sequences and cut the DNA at that point

4. Overview cont.
Since everyone has a different nucleotide sequence (base pair sequence) in their DNA, everyone’s DNA gets “cut” at different spots
Since everyone’s DNA gets “cut” at different spots, everyone’s DNA fragments will be different sizes

5. ELECTROPHORESIS APPARATUS
DNA fragments are separated from each other by using electrophoresis.
Electrophoresis will separate fragments based on their size and charge.
The apparatus includes a gel chamber and power supply

6. SEPARATING DNA FRAGMENTS
DNA samples will be loaded in wells of the gel, covered with a buffer solution, and exposed to an electric current for several minutes.
DNA carries a negative charge on its molecule and will be attracted to the positive pole of the apparatus.
Smaller fragments will move through the gel faster than the larger ones.

7. The gel will be removed from the chamber and stained for viewing.
Staining Viewing

8. DNA BANDING PATTERNS
The bands of DNA represent different size fragments.
By measuring the distance the band traveled, the size of the fragments can be analyzed, compared to different samples, and used to more definitively determine “guilt.”

9. See DNA4 for a discussion of analysis techniques.
THE END
See DNA4 for a discussion of analysis techniques.