Mystery of the Stolen Cat Food

Name:

Period:

The Scenario:

Fluffy is my white haired cat.   She sometimes likes to have her meals on the back porch, so I put her dish of cat food outside.   Recently she's been whining and complaining because she's hungry.   After doing a little detective work, I suspected that another cat has been eating Fluffy's food.   I placed a new bowl of cat food on the porch and kept Fluffy inside.   When I opened the door to look outside, there was a white cat running away from the food dish.    However, there are 3 other white haired cats in my neighborhood and I can't tell which cat is eating Fluffy's food.   You are going to help me figure out which cat is the criminal!

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 which cat is eating Fluffy's food?

What tricks can we use to see DNA?

Materials

• DNA from cat suspect #1, cat suspect #2, cat suspect #3, and the cat dish (X)
• agarose (0.8% in TAE)
• Tris-acetate/EDTA solution (TAE)
• micropipette/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 and set to 100 V. 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 20-25 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:

What can your data tell you about which cat suspect committed the crime?

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BIOTECH Project Department of Molecular and Cellular Biology The University of Arizona September 18, 2000 Last Modified March 1, 2002 http://biotech.biology.arizona.edu