Recommended for: Grades 9-12

Lesson Plan: DNA Fingerprints

Lesson Plan
Standards

Overview

In this lesson, students learn how DNA fingerprinting has been used in criminal investigations. They do an interactive Web activity to learn about the process of DNA fingerprinting. In teams, they interpret different DNA fingerprints, then do a jigsaw activity to explore other uses of DNA forensics. Finally, they listen to a radio program about using DNA as evidence and discuss the limitations of and problems with DNA testing.

Objectives

Understand how DNA fingerprinting can be used in criminal investigations
Describe the process of DNA fingerprinting
Learn which part of the DNA genome is used for DNA fingerprinting
Understand the factors that can increase the accuracy of DNA fingerprinting
Interpret DNA fingerprints
Explore various uses for DNA fingerprinting
Recognize the limitations of and problems with DNA testing

Suggested Time

Two to three class periods.

Multimedia Resources

Forensic DNA Analysis QuickTime Video
Create a DNA Fingerprint Shockwave Interactive
How DNA Evidence Works PDF Document
DNA Fingerprint Photos PDF Document
DNA on the Witness Stand PDF Document
DNA Makes History PDF Document
Forensics HTML Document
Dab of DNA Helps Keep Counterfeiters at Bay PDF Document
DNA Evidence QuickTime Audio

Materials

Index cards for steps of DNA fingerprinting
Tape
DNA fingerprint cards

Before the Lesson

Review the concept of DNA and the different components of the DNA code.
Make copies of DNA fingerprint photos and cut up and paste on cards. Make enough sets for teams of four students.
Make copies of articles for jigsaw teams.

After the Lesson

Optional: Do the Forensic Lab Activity, DNA Fingerprinting at
http://www.accessexcellence.org/AE/ATG/data/released/0157-theasinclair/Heading7.html .

The Lesson

Part I

1. Show the video Forensic DNA Analysis. Discuss the following:

What does the DQA1 DNA test identify?
What are the advantages and disadvantages of this method?
Can the results of this test accurately pinpoint the source of the blood? Why or why not?

2. Have students do the Create a DNA Fingerprint Web activity. Then give student teams index cards and ask them to write the name of each step of the DNA fingerprinting process on the front of a separate card, with an explanation for the step on the back. Ask teams to put the cards in order according to the sequence of steps. Then have students shuffle the cards and put them back in order. Have each team tape their cards in order to the board and compare their sequences and explanations to those of other teams. Ask different students to explain what happens in each step.

3. Have students read and take notes on the article How DNA Evidence Works. Then have the same student teams as before answer these questions:

What are VNTRs, and why are they valuable for DNA fingerprinting?
How do the steps for fingerprinting DNA described in this article compare to the steps on your index cards? What new information about the process did you learn?
What are some other uses for DNA fingerprinting (e.g., paternity testing, identifying missing people or victims of war or disasters)?
Why is DNA fingerprinting called "a numbers game"? What increases the accuracy of DNA fingerprinting?

Point out that the DNA fingerprinting technique described in the article, VNTR profiling, is sometimes called Southern Blotting. (The process by which DNA fragments are blotted off the gel and transferred to the nylon membrane was designed by a scientist named Southern.) The analysis is also referred to as RFLP (Restriction Fragment Length Polymorphism). This technique is commonly used in fingerprinting when there is enough DNA available.

The DQA1 DNA test used in the video about Sam Sheppard was a different process that used a genetic marker, DQA, to identify individual alleles. This test is simpler and faster than VNTR profiling and can be used with small quantities of DNA, which are amplified by the Polymerase Chain Reaction (PCR) process. But since about 7 percent of the population have the same DQA type, the test can distinguish different individuals only 93 percent of the time. That's not good enough to convict someone, but the test can quickly clear someone who has been wrongfully accused.

4. Give teams of students a set of the DNA fingerprint cards. Ask them to interpret the fingerprints and compare their answers to those of other teams when they are finished. Provide a key of the correct answers.

Part II

5. Have students do a jigsaw activity to explore other examples of how DNA fingerprinting has been used (Jigsaw Explanation (PDF)). Use the sources listed below. Divide DNA on the Witness Stand into sections if necessary.

DNA on the Witness Stand PDF Document
DNA Makes History PDF Document
Forensics HTML Document
Dab of DNA Helps Keep Counterfeiters at Bay PDF Document

Have students listen to the NPR "All Things Considered" audio program DNA Evidence. Ask pairs of students to consider and discuss these key questions:

What issues and concerns about DNA testing are raised in this program?
Do you think that anyone who is arrested should be required to have his or her DNA tested? Why or why not?
What safeguards, if any, should there be on future uses of DNA databases?

6. Ask students to report to the class three things they learned about DNA fingerprinting that they found surprising. Or, have students use the term DNA Fingerprint as an acronym. Have students in teams brainstorm what they have learned about this topic and then organize this information into sentences that begin with each letter of the acronym. Ask them to include the most essential information about the topic. For example:

DNA sections with repeating sequences are called VNTRs and are used in DNA fingerprinting.
No DNA fingerprint test can prove defendant's guilt, but a match can establish probability.
A fingerprint begins with a sample of tissue such as blood, skin, or semen.

Fingerprinting can also be used to determine paternity and to identify victims of disasters or war.
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Gel electrophoresis separates the DNA fragments by size, as the smaller pieces move faster through the gel.
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Restriction enzymes break DNA into more manageable sizes for fingerprinting.
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