Todd Family Mystery

Name:

Period:

The Scenario:

Last year Todd was an 8th grader at MLK Middle School in Salt Lake City, Utah. Todd is a pretty normal kid, but he had some things that always bugged him about his family, he did not look anything like his Mother and Father, nor his brother and sister. They all had brown hair and brown eyes, and even had dark complexion. Todd on the other hand had blue eyes, blonde hair and had a fair complexion. He also felt like he was very different personality wise, and his siblings always teased him that he had been switched at birth. In 8th grade Todd learned about genetics, and learned that there was a way to determine whether or not he was his parents’ child and, with his parents’ permission, we can help him confirm or deny his current biological parentage.

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

What is DNA and what does it do?

What are chromosomes and how many copies do you have in each of your cells? Where did they come from?

How is DNA passed on differently in the offspring of sexual reproduction compared to asexual reproduction?

How much DNA do you share with each of your parents? How much DNA do you share with your siblings?

What are some characteristics or properties of DNA?

How can we take advantage of these properties to help us figure out if Todd is the son of his parents Frank and MaryAnn?

Materials

• DNA from Frank, MaryAnn, Todd and his two siblings John and Anastasia
• agarose
• 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. Why near the black electrode?

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?
   
   Draw a picture of your gel and label which samples will be added to which wells before you add DNA.
   
   
   

3. Load your DNA SAMPLES into the wells, be sure to keep track of which samples you loaded in which lanes.

4. Now pour TAE solution over your gel CAREFULLY so that is it completely covered plus a little more. What do you think the TAE solution is for?
   

5. 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? If time permits, you will run the gel for about 30 minutes.
   
   
   

Analyzing Your DNA Data

Plug in your gel electrophoresis tray, and after 15 minutes draw a picture.

What can your data tell you about the relationship of Todd with Frank and Maryann?Is Todd the son of Frank and Maryann?

How much DNA do Todd and John share? Can you determine Todd and John’s relationship from the results of their two DNA samples? Please Explain.

What if you compared John with Frank and Maryann, does this help in determining the relationship of Todd and John? Please Explain.

How much DNA do Todd and Anastasia share. Can you determine a relationship between Todd and Anastasia using these DNA samples?

What chance do siblings have sharing bands in this DNA fingerprinting technique?

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