Lab# ________: DNA Fingerprinting Simulation
____________
Date
Introduction:
Electrophoresis is a standard molecular biological technique for separating nucleic acids by size and
electrical charge. Nucleic acid samples are placed in a special gel and subjected to an electric field.
Negatively charged fragments move toward the positive electrode while positively charged fragments
move toward the negative electrode. Smaller molecules move through the gel the most easily and so tend
to move the farthest, while larger molecules have more difficulty moving through the gel and so tend to
remain closer to the starting place. After the samples have been separated, the resulting bands are stained
so that they can be seen.
Gel electrophoresis is used to provide genetic information in a wide range of fields. One important
application is the analysis of human DNA to provide evidence in criminal cases. Samples at a crime
scene may be obtained from any DNA-containing tissue or body fluid, including blood, skin, hair, or
semen. In many cases a technique called polymerase chain reaction (PCR) is used to amplify specific
regions of DNA that are known to vary among individuals. Using this technique, samples as small as 20
cells can produce enough DNA for analysis. The DNA sample that is obtained is cut into fragments using
restriction enzymes that cut the DNA at specific sequences. These fragments can then be separated using
electrophoresis The specific pattern obtained (usually marked with radioactive probes in actual cases) is
unique to each person’s genetic make-up. This pattern is called a DNA fingerprint.
In this lab you will help to simulate a crime scene analysis. You will receive a section of DNA and act as
the restriction enzyme, cutting the DNA in the specific pattern for your restriction enzyme. You will then
separate your fragments based on the number of nucleotides they contain. Comparing your results to
others in the class should allow us to find the guilty party.
Procedure
1. Obtain a DNA sequence from one of the suspects or the crime scene. Record where your sample is
from.
2. Obtain a restriction enzyme assignment with instructions.
3. Cut your DNA sequence into fragments based on your restriction enzyme instructions.
4. Count the number of bases in each of your fragments and write the number on the back.
5. Take your fragments to the “electrophoresis gel” poster board and load your sample into your
assigned well.
6. When we “turn the power on”, your group will move your fragments to the correct positions based on
the number of bases they contain.
7. When all of the fragments are separated, sketch the resulting patterns on the grid provided.
8. Compare the patterns to see if you can determine which of the suspects has a DNA fingerprint that
matches the samples from the crime scene.
# bases
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
Crime Scene
Sample
Sample from
Suspect #1
Sample from
Suspect #2
Sample from
Suspect #3
Sample from
Suspect #4
Conclusion
Based on the results of our simulated DNA fingerprinting and on the results of the actual electrophoresis
demonstration, write a crime report detailing which, if any, of the suspects you believe was at the crime
scene. Cite specific evidence to back up your conclusions.