What is DNA Fingerprinting? Case of the Bloody Micropipettor- Student Handout

Late one evening last week the police received a call about a murder in the laboratory of the biotech company GeneSmart. When the police arrived at the company headquarters the police noted that the point of entry had been through the glass window in the door,, The police also notice a small amount of smeared blood on the glass. Lying face down on the floor next to the lab bench was the body of Mr. Skinner, the research director. Underneath the body, the inspectors found the murder weapon, a bloody micropipettor.

The police apprehended Mr. Runyon and Mr. Bell, two former researchers at GeneSmart. Both suspects denied all knowledge of the murder and willingly provided the police with a blood sample.

The Chief Inspector ordered DNA tests on the victim Mr. Runyon and Mr. Bell and blood from the broken glass. You will analyze the DNA samples from the investigation using agarose gel electrophoresis. Based on your DNA analysis, you will determine who should be included as a suspect in the murder.

Some questions to get you thinking about today's lab:

What is DNA and what does it do?

What are some characteristics or properties of DNA?

How can we take advantage of these properties to help us figure out whose DNA was at the crime scene?

What tricks can we use to see DNA?

Materials

• DNA from Mr. Skinner #1, Mr. Runyon #2, Mr. Bell (#3), and broken glass (X)
• 0.8% agarose in TAE
• Tris-acetate/EDTA solution (TAE)
• micropipette and tips
• electrophoresis apparatus

Procedure:

1. Get your electrophoresis apparatus. Make sure the comb is placed closest to the black electrode and that there are stoppers at both ends of the gel space.

2. Pour hot agarose into the gel space until it reaches the top of the gel box. Let the agarose harden, which should take about 10 minutes. Don't touch/move your gel until it's hard. Why not?

3. When the agarose gel is hard, take out the stoppers and gently remove the comb. Draw a picture of your gel and label which samples are where before you add DNA to the gel.
   
   
4. Load your DNA SAMPLES into the wells near the BLACK ELECTRODE. Why near the black electrode? Be sure to keep track of which samples you loaded in which lanes.
   
   
5. Pour the TAE solution into the side farthest from you samples, so that you gels is completely covered plus a little more. What do you think the TAE solution is for?
   

6. Run that gel!! Plug the electrodes into your gel box (red to red, black to black), being careful not to bump your gel too much. Plug the power source into an outlet. How can you tell your gel is running?
   
   
   

Analyzing Your DNA Data

Plug in your gel electrophoresis tray, and after 3 minutes draw another picture.










After 15 minutes draw another picture.





Once the purple dye has migrated approximately 2/3 of the gel, turn off the power and carefully remove the gel. The gel is very fragile, take care to not break it. You can remove the tray that you poured agarose on to and gently slide the gel into the staining tray. At this point you cannot see the DNA, what can you see and how do the four different lanes compare?

Once you have placed your gel into the staining tray bring it to the staining station. Completely cover the gel with methylene blue and cover try with saran wrap. Stain overnight.

Next day--Viewing the gel: Pour the methylene blue back into the bottle and carefully place the gel onto a white light box. The gel is very fragile so take care to not break it. Draw a picture of your stained gel, be as accurate as possible in drawing the bands:

Should Mr. Runyon be included or excluded as a suspect? Explain your answer



Should Mr. Bell be included or excluded as a suspect? Explain your answer.

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   BIOTECH Project Department of Molecular and Cellular Biology The University of Arizona Designed by: Ken Kubo, Ph.D. Last Modified March 1, 2005 Nadja Anderson, Ph.D. nadja@email.arizona.edu http://biotech.biology.arizona.edu