1. DNA Fingerprinting

2. DNA Fingerprinting
A technique used by scientists to distinguish between individuals of the same species using only samples of their DNA.
Invented by Alec Jeffreys at the University of Leicester in 1985 (Now Sir Alec Jeffreys)

3. Steps in DNA Fingerprinting
Step one:
Collect the DNA sample which can be obtained from most tissues (blood, semen, vaginal fluid, hair, skin, etc.)
Step two:
Break down the cells to release the DNA (not unlike our strawberry lab)

4. Steps in DNA Fingerprinting
Step three:
Restriction enzymes are used to cut the DNA at specific points in the base sequence resulting in ‘restriction fragments’.
Because everyone’s DNA is unique, different sized restriction fragments are produced.

5. Steps in DNA Fingerprinting
Example: The Hae III enzyme will cut DNA only in the middle of a sequence of G C G C G C. While Eco RI will cut only between the G and A in the G A A T T C segment
Sample segment of DNA
C G A T C C G C G C G C T G C A G A A T T C T
G C T A G G C G C G C G T C G T C T T A A G A
Other restriction enzymes will cut only at other specific points.
Given the size of DNA, and the use of additional restriction enzymes, thousands of restriction segments are created.

6. Steps in DNA Fingerprinting
Step four:
Gel Electrophoresis: Separates the fragments based upon their size.
DNA has a negative charge.
The samples are placed in a gel and an electric current is passed through it.
Shorter fragments travel farther through the gel toward the positive end.

7. Steps in DNA Fingerprinting
Step five:
A radioactive substance that is drawn to DNA is added.
This allows a type of photograph to be obtained.
The patterns of the fragments are then analyzed.

8. Analyzing a DNA Fingerprint
Crime:
Compare the DNA segments found at the scene with the segments from the suspects.
All of the perp’s segments should match up with those found at the scene.

9. Analyzing a DNA Fingerprint
Paternity Cases:
A bit trickier because the offspring receives ½ of their DNA from mom and ½ from dad.
First match up the offspring’s DNA with the mother’s (this is certain)
Any of dad’s DNA that matches the offspring’s DNA, that does not also match the mom’s DNA, indicates that that is the father.