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Personal DNA Testing

Classroom Activity


Activity Summary
Students investigate the genetics behind why people respond differently to the same drug.

Learning Objectives
Students will be able to:

  • state that DNA is the genetic material of all living things.

  • explain that single-nucleotide polymorphisms, or SNPs, are a type of change in the genetic code in which one base (i.e., adenine, cytosine, guanine, or thymine) is substituted for another.

  • explain that SNPs may be associated with different diseases or different responses to medications.

  • analyze a set of data and draw conclusions.

Suggested Time
One class period

Materials for each team

Background
In 2001, scientists announced the successful completion of the Human Genome Project—the years-long endeavor to determine the order of the three billion DNA base pairs that make up the tens of thousands of genes in the human genome. Completion of the project was just the first step in a new era of genomics research—with the sequence in hand, scientists are free to analyze the genome to learn more about how our DNA affects who we are.

Scientists make sense of the sequence data from the Human Genome Project by looking for people's differences at the level of their DNA. The DNA sequence from one person to the next is remarkably similar, but tiny variations do occur, rendering each of us a unique individual. In fact, the most common type of variation in the human genome is the single-nucleotide polymorphism, or SNP (pronounced "snip"). This is a single base-pair change in a segment of DNA—replacement of a C (cytosine) with a G (guanine), for example. You may wish to break down the term "single- nucleotide polymorphism" for your students by explaining that "poly-" means "many," and "-morph-" means "form." So a "single-nucleotide polymorphism" means a site where one nucleotide (or letter) in the genetic code may take on many forms.

Tell your students that a SNP is a location in the genetic code that can be different in different people. To help them understand what a SNP looks like and how scientists scan for them, write the following three sequences, including the row of numbers above the letters, on the board:

123456
AATCGA

AAACGA

AAGCGA

Explain that scientists read these sequences from left to right, just as we read words on a page, and they assign a position to each letter in sequence. Ask your students what they notice about these sequences. Point out that one position in each sequence contains a letter that differs from the others in that position, and that this position is called a SNP. In the first sequence, this SNP would be called "3T," meaning it is a SNP at the 3rd position in the sequence, and the nucleotide at that position is a thymine. The subsequent SNPs are 3A and 3G. You may need to walk through a few examples to be sure students see how to recognize SNPs in a length of genetic code.

SNPs most often occur outside of genes, but they do sometimes occur within genes themselves. In these cases, SNPs may affect gene function by subtly changing the structure of the protein the gene encodes. But the vast majority of SNPs are simply changes in the nucleotide at a specific position outside of the gene's coding region, with no change in the organism's phenotype, or physical traits.

As students discover in the Personal DNA Testing NOVA scienceNOW segment, scientists are learning how to use SNPs as indicators of certain diseases. SNPs themselves don't cause a disease; rather, they are identified with it. Most often, SNPs that are located close to a gene are associated with different versions, or alleles, of the gene. This close association gives researchers the ability to predict which allele a person has based on his or her SNP profile. Researchers also are increasingly using SNPs as markers that help predict how a patient may respond to different kinds of drugs.

A group of SNPs located near a gene called ADRB2 appears to predict how asthma patients respond to the asthma medication albuterol. The gene itself produces a protein that is embedded in the muscle cells lining the lungs; when the gene expresses this protein, the muscles relax. Albuterol activates this protein, causing the bronchial muscles to relax and relieving the symptoms of an asthma attack. Some patients respond very well to the drug, while others experience little or no relief, and researchers today are trying to determine how SNPs may be related to patient responses to albuterol. In the future, doctors may be able to screen patients' DNA to help predict how they will respond to certain medications—whether a drug will be effective, offer no relief, or even turn out to be harmful to them.

In this activity, students take on the role of researchers trying to determine the best course of treatment for five asthma patients. In this scenario, a recent large trial of three fictitious asthma drugs has just ended, and the study shows that genetic profiles could help predict patient responses to the medications. Based on the results of this "study," students will analyze five patients' SNP profiles and recommend a course of treatment for each.


Procedure Before the Lesson The Lesson
  1. Review the terminology students were introduced to in the segment. Ask for a volunteer to define "SNP" and to explain what question Neil DeGrasse Tyson, the host of the segment, was seeking to answer by having his DNA analyzed. You may need to redefine the term "SNP" or explain in more detail what it means. In the segment, the host had his DNA analyzed for SNPs associated with a gene called APO E4. Having this gene is associated with a higher probability that a person will develop Alzheimer's disease later in life.

  2. Divide the class into teams of two. Present the following scenario to the class:

    • They are clinical researchers investigating how patients with different genetic profiles (combinations of SNPs) respond to three fictitious asthma drugs that are in development at a drug company.
    • The company's goal is to determine which drug works best for the greatest number of people and carries the fewest side effects.
    • As clinical researchers, students must determine the genetic profile or profiles associated with positive responses to the drug. They also must determine whether any patients should be advised to avoid the drug based on specific genetic profiles.
    • They will launch this research with a DNA analysis of five patients who came to their clinic two weeks ago seeking relief for seasonal asthma. At the time, a technician at the clinic took a saliva sample from each patient and sent it to a laboratory that sequenced a short segment of DNA in the region of a gene associated with asthma. Today, the results have arrived.

  3. Distribute the DNA Testing in the Clinic handout and have your student researchers complete it.

Extension: Discuss a real-world example in which physicians use SNP profiling to predict whether a drug is appropriate for certain leukemia patients. Direct the class to watch the animation Beyond the Stethoscope: Your Doctor's New Tools. Use the animation to start a conversation about the field of pharmacogenomics, which uses genetics to predict patient responses to various drugs.

For another extension activity, you also may direct students to take the poll in Four Tests, and discuss their reactions to the scenarios presented. What are some of the benefits of genetic testing? What are some of the drawbacks?


Activity Answer

DNA sequence readouts

Nucleotide position 1 2 3 4 5 6 7 8 9 10 11 12 13
Adam G A C C T G C T T A A C G
Renee G A C C T G C T C A A C G
Karla G A A C T G C T A A G C G
Lon G A G C T G C T A A A C G
Rosie G A G C T G C T G A A C G

Note: Students are only expected to note the drug or drugs they would recommend for each patient, as well as whether they would need to provide a warning about side effects

Adam
SNP Profile: 3C 9T 11A
Drug name: BreatheMor Inhaleze Relaxxalung
Recommended for this SNP profile? (y/n) No, not effective for this SNP profile No, not effective for this SNP profile Yes, effective for this SNP profile
Precautions or warnings for the patient? Yes, trial patients broke out in a rash Yes, 17% of patients with this profile developed blurred vision Yes, 20% of patients with this profile broke out in a rash

Renee
SNP Profile: 3C 9C 11A
Drug name: BreatheMor Inhaleze Relaxxalung
Recommended for this SNP profile? (y/n) Yes, effective for this SNP profile Yes, effective for this SNP profile No, not effective for this SNP profile
Precautions or warnings for the patient? No side effects reported for this profile Yes, 15% of patients with this profile developed blurred vision Yes, 21% of patients with this profile broke out in a rash

Karla
SNP Profile: 3A 9A 11G
Drug name: BreatheMor Inhaleze Relaxxalung
Recommended for this SNP profile? (y/n) No, not effective for this SNP profile No, not effective for this SNP profile No, not effective for this SNP profile
Precautions or warnings for the patient? Yes, 8% of patients with this profile reported headaches No side effects reported for this profile Yes, 7% of patients with this profile had uncontrollable hiccups for 30 minutes or longer

Lon
SNP Profile: 3G 9A 11A
Drug name: BreatheMor Inhaleze Relaxxalung
Recommended for this SNP profile? (y/n) No, not effective for this SNP profile Yes, effective for this SNP profile No, not effective for this SNP profile
Precautions or warnings for the patient? No side effects reported with this profile No side effects reported with this profile No side effects reported with this profile

Rosie
SNP Profile: 3C 9T 11A
Drug name: BreatheMor Inhaleze Relaxxalung
Recommended for this SNP profile? (y/n) No, not effective for this SNP profile Yes, effective for this SNP profile Yes, effective for this SNP profile
Precautions or warnings for the patient? No side effects reported with this profile No side effects reported with this profile Yes, 18% of patients with this profile broke out in a rash
  1. Describe what the term "SNP" means. Illustrate your answer by drawing a hypothetical length of DNA from three different people, showing three locations that are SNPs.
    A SNP is a position in the genetic code that can be different in different people. For example, the people below have a SNP at position 3:
    CCATGA
    CCTTGA
    CCGTGA
  2. Based on the results of the large-scale clinical trial, which drug provides relief to the greatest number of patients with the lowest risk of side effects? Which drug provides relief to the greatest number of patients overall?
    BreatheMor provided relief to 40% of patients with no side effects. Inhaleze benefits 59% of patients, but some of them experienced side effects.
  3. Based on the trial results, which drug helped patients with the rarest SNP profile? Did people with this profile experience relief with either of the other two drugs?
    Inhaleze also helped people with the rarest SNP profile (3G 9A 11A). People with this profile did not experience relief from either of the other two drugs.
  4. If the pharmaceutical company could develop only one of the drugs, which should it develop? Explain your reasoning.
    There are no correct answers here; look for evidence that students weigh the costs and benefits of any decision. A sample answer may be: The company should develop the drug (BreatheMor) that benefits the most people without side effects, because at least it will help some portion of the population with minimal risk.
  5. If the company could develop two of the three drugs, which two should it pursue? Why those and not another combination?
    There are no correct answers here; look for evidence that students weigh the costs and benefits of any decision. A sample answer may be: If it can develop two drugs, then I think it should develop BreatheMor and Inhaleze, because Inhaleze works for more patients, even though it has some risk of side effects.
  6. What are some advantages to genetic testing? What are some drawbacks?
    Some advantages are that it could help doctors pinpoint better treatment options for patients and reduce the risk of giving people drugs to which they may react poorly. Drawbacks include privacy concerns and the ethical questions raised when testing for conditions for which there are no current treatments. Also, scientists are still learning how genetic differences are associated with disease; a straightforward genetic scan might not supply all the information they need.

Use the following rubric to assess each team's work.

Excellent Satisfactory Needs improvement
Completing handouts
  • Students correctly identify SNPs in each patient and can explain how they identified the SNPS.
  • Students show ability to apply information from large-scale trial to individual patients and make recommendations for an effective course of treatment.
  • Students have clear understanding of real-world applications of SNP analysis.
  • Students need assistance while trying to determine SNP profiles of different patients.
  • Students only partially complete the charts and handouts and have limited understanding of the real-world applications of SNP analysis.
  • Students have difficulty identifying SNPs or explaining SNPs in their own words.
  • Students make little effort to complete patient charts and have difficulty connecting this activity to a real-world situation.

Standards

The "Personal DNA Testing" activity aligns with the following National Science Education Standards (see books.nap.edu/html/nses).

Grades 9-12
Life Science

  • Molecular basis of heredity


Science in Personal and Social Perspectives

  • Personal and Community Health



Classroom Activity Author

Jennifer Cutraro and WGBH Educational Outreach Staff

Jennifer Cutraro has 12 years of experience in science writing and education. She has written text and ancillaries for Houghton Mifflin, K12, and Delta Education and has taught science and environmental education at science centers across the country. She also contributes news and feature stories about science and health to media outlets including The Los Angeles Times, The Boston Globe, Science News for Kids and Scholastic Science World.

Teacher's Guide
NOVA scienceNOW: Personal DNA Testing
WATCH THE VIDEO ONLINE PROGRAM OVERVIEW VIEWING IDEAS CLASSROOM ACTIVITY RELATED NOVA RESOURCES


WebsiteFour Tests Flash Interactive
WebsitePersonal DNA Testing QuickTime or Windows Media segment
   

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