Solving the Mystery using Restriction Enzymes and Gel Electrophoresis

Introduction:
a) Restriction enzymes are a specific type of protein which can be found in bacteria. They act as a defense against viruses by cutting up viral DNA at specific locations called palindromes (these specific sites can also be called restriction sites). Gel electrophoresis is a process used to analyze DNA - the DNA is placed in a gel and an electric current is sent through. DNA is negatively charged, thus it will be pulled toward the positive node. However, the smaller, lighter pieces of DNA can move faster and travel farther along the gel. If this cut-up DNA is run on a gel, we can determine the length of each fragment of DNA based on how far they traveled along the gel. The different fragments can be seen as dark bands along the gel. This is called Restriction Fragment Length Polymorphism (RFLP).
b) The purpose of this experiment is to analyze different suspects' DNA via gel electrophoresis and compare their DNA to the crime scene's. The suspect whose DNA matches the crime scene's (meaning the bands are the same) is the culprit.
c) The purpose of the restriction enzymes is to cut up the suspects' DNA - each person has a unique genetic code, thus each person's DNA will be cut at different locations and will result in unique DNA fragment lengths. A loading buffer containing blue dyes is added to the DNA samples before injection into the gel - this allows us to monitor the process of gel electrophoresis. The gel electrophoresis and RFLP will then show a unique banding pattern of each person's DNA fragment lengths on a gel.  We can then analyze these bands to determine which DNA matches the DNA of the crime scene.
d) I cannot predict which person will be the culprit since I have not seen the results yet. However, the control is the crime scene DNA and the variables are the suspects' DNA.

Procedure:
Basically explained above...

Results:
It turns out Suspect #3 was the criminal! The DNA bands from Suspect #3 clearly matched the DNA bands of the Crime Scene - the evidence is incriminating.

Discussion:
a) Via gel electrophoresis, the fragments were separated by length along the gel - the shorter fragments traveled farthest toward the positive node while the longer fragments remained further behind. By comparing the bands, it was clear that the DNA bands of Suspect #3 exactly matched the bands of the Crime Scene.
b) Possible sources of error:

• Improper pipetting
• Contamination of DNA
• Not run on the gel long enough to accurately disperse DNA fragments