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Student Exploration: DNA Profiling
Vocabulary: DNA polymerase, DNA profiling, gel electrophoresis, gene, mutation, non-coding region, polymerase chain reaction, primer, short tandem repeat
Prior Know
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Student Exploration: DNA Profiling
Vocabulary: DNA polymerase, DNA profiling, gel electrophoresis, gene, mutation, non-coding region, polymerase chain reaction, primer, short tandem repeat
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
In 1985, Darryl Hunt was convicted of murder. While Hunt was in jail, a new method for analyzing DNA evidence was invented. The DNA evidence on the victim did not match Hunt’s DNA but did match that of another prisoner. After 19 years spent behind bars, Hunt was finally declared innocent and released from prison in 2004.
1. DNA is used to tell people apart. What aspects of DNA do you think make this possible?
2. What are some possible uses for technology that can identify people based on their DNA?
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Gizmo Warm-up
DNA profiling does not just compare people’s entire genome side by side. Instead, a very particular part of the DNA is compared. In the DNA Profiling Gizmo you will learn about the differences in DNA that make DNA profiling possible and you will use that knowledge to design your own DNA profiling test.
Click on the crime lab in the Forensic training section. You are looking at a strand of DNA. DNA contains genes and non-coding regions between genes. Click on Non-coding A.
1. You are looking at a portion of the non-coding A section for three different people. Are these sections the same or different? Explain.
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Activity A: Forensic training Get the Gizmo ready:
● Click on Forensic training and Start again.
Introduction: In this activity, you will learn about the principles and techniques that make DNA profiling possible. Genes code for specific traits. In people, the DNA sequences for most genes are nearly identical, since any change could result in a harmful disorder. The areas between genes do not code for any essential traits, so a change to the DNA sequence doesn’t have any major consequences. As a result, these regions tend to be very different for different people.
Question: How can the differences in DNA be exploited to perform DNA profiling?
1. Observe: Click on non-coding A. What do you see in the middle of each of the three DNA sequences?
2. Compare: Turn on Show short tandem repeats (STRs). An STR is a short, repeated sequence of DNA, like TAAA. They can be repeated any number of times without affecting the traits of the person. Different people usually have different numbers of repeats.
What does this do to the length of each person’s non-coding regions?
3. Create: Your goal is to make copies of the STR region. To do this, you will make primers that surround the STR region. A primer is a short sequence of DNA that acts as a starting point for DNA replication.
Click Next. Click on person 1’s DNA to separate the two strands. Drag along the AAGGC nucleotides, and then the TCGCC nucleotides to create primers. Click Next. The Gizmo will add the same primers to the two other people.
What do you notice about where the primers attach in each person?
4. Observe Click Next. An enzyme called DNA polymerase uses the primers as a starting point to copy the DNA. Copying DNA using primers is a technique called Polymerase chain reaction (PCR).
Click Next again. The DNA segments are copied millions of times.
What do you notice about the lengths of the copied DNA strands?
Activity A (continued from previous page)
5. Compare: Click Next. Gel electrophoresis is used to separate DNA strands of different lengths. An electric current is passed through the gel. As the current moves from top to bottom, it pulls the DNA and loading dye along with it. Click on the power box to turn it on.
A. Which person’s DNA band travelled the farthest? Shortest?
B. Turn on Show labels. What do you notice about the length of the DNA versus the distance it travelled down the gel?
C. Can you identify people by comparing the length of STR regions on a gel? Explain. (2)
6. Observe: Click Next. Then select Gene A.
A. Does gene A have any STRs?
Because genes are segments of DNA that hold the instructions for producing proteins, they usually don’t have large variable regions like STRs.
B. Are there any differences in gene A between the individuals? Look carefully
Genes may contain small mutations that don’t affect the length of the segment.
C. Create primers and copy the DNA. What do you notice about the length of the duplicated regions?
D. Click Next and turn on the gel electrophoresis apparatus. What do you notice about the position of the band?
E. Can you identify people by comparing the length of genes on a gel? Explain. (2)
7. Summarize: How can PCR and gel electrophoresis be used to identify people?
Activity B:
Design and test primers
Get the Gizmo ready:
● Select Design primers on the left.
Introduction: To identify people based on DNA, copies of certain segments of DNA are compared using gel electrophoresis. In this activity, you will design primers that will copy segments of DNA that will help to identify people.
Question: How can you use your knowledge to create a DNA profiling test?
1. Predict: Gel electrophoresis distinguishes DNA segments by length. To identify people by DNA, is it better to make copies of genes or non-coding segments? Explain.
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2. Create: Pick a section of DNA you want to copy and follow the directions to create primers.
A. Click Preview primer. Did the DNA copy properly?
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