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Sickle Cell Anemia: A Case Study Approach to Teaching High School Genetics

Teacher: Jeanne Ting Chowning
School: BioLab, Seattle, WA
Grade Level: 10-12

Download: This case study and all associated activities, masters, and worksheets can be downloaded in PDF at the GENETICS download page.

Summary:
Sickle cell anemia is an example of a genetic disease that can serve as a vehicle for teaching many biology concepts. Using a case study approach, opportunities arise to make connections not only to various aspects of genetics and molecular biology, but to physiology, evolution and societal and ethical issues as well.

Instructional Materials (included at this website):

• Sickle Cell Anemia and Genetics: Background Information.
• Allele Frequencies and Sickle Cell Anemia Lab. Student instructions, data sheet, analysis questions, overhead master.
• Sickle Cell Anemia: Blood Video Questions and Translation Practice Worksheet.
• Sickle Cell Lab: Diagnosis Using Simulated Restriction Analysis of DNA.
  --PreLab reading and questions
  --Student instructions and questions
  --Teacher information

List of Classroom Activities:

• Mystery of the Crooked Cell PreLab Activities (includes viewing slides of normal and sickled red blood cells).
• Viewing Blood is Life video.
• Sickle Cell Anemia: Blood Video Questions and Translation Practice Worksheet.
• Sickle Cell Anemia: Diagnosis Using Simulated Restriction Analysis of DNA.
• Viewing Children by Design video.
• Bioethical Decision-Making.
• Allele Frequencies and Sickle Cell Anemia Lab.

Description:
Before beginning the unit, briefly review the circulatory system and the normal functions of its components, which were covered earlier in the semester. Then begin the sickle cell unit with the prelab activities described in "Mystery of the Crooked Cell." Students are presented with the symptoms of a patient with an "unknown" disease and must hypothesize its cause after completing four 10-20 minute prelab exercises, which include: examining slides of diseased and normal red blood cells (RBCs), modeling the occlusion of capillaries by sickled RBCs with hands-on manipulatives, using balloons and beads to build simple models of RBCs containing either normal or mutant hemoglobin, and determining the inheritance pattern of the disease based on the patientís family history.

Extending the analysis of blood and hemoglobin in the prelab activities, students view the three-dimensional structure of hemoglobin on the Internet. Students watch Blood is Life, a video that teaches about blood from the perspective of a young school teacher with sickle cell anemia. Students complete the Sickle Cell Anemia: Blood Video Questions and Translation Practice Worksheet , which reviews key concepts in the video and provides practice in conceptual transcription and translation of the b globin gene, both normal and mutant.

Sickle cell disease provides a clear example of how changes in DNA can result in an altered protein. Dry labs or exercises such as the Translation Practice Worksheet can be used to illustrate this connection. How can the disease be diagnosed? How can people with a family history of the disease learn whether they carry the trait? Discuss how the answers to these questions can be found by using restriction enzymes to analyze the DNA that codes for b globin and how hemoglobin itself can be analyzed by protein electrophoresis. Students can simulate a restriction analysis of wildtype and mutant b globin genes by eletrophoresing dyes through an agarose gel, as described in Sickle Cell Anemia: Diagnosis Using Simulated Restriction Analysis of DNA .

These activities lead naturally to the topic of genetic testing and a discussion of the ethical concerns that surround such testing. Use current newspaper and magazine articles related to genetics issues to get students thinking and stimulate discussion. Or watch one of several videos that deal with these issues, such as Children By Design, which includes segments on genetic testing, gene therapy, and medical selection of disease-free early embryos for implantation. To make decisions about genetics-related ethical issues, such as denying a person insurance coverage or employment based on his or her genotype, an ethical decision-making model like that developed by the Hastings Center can be used.

Sickle cell anemia, which is inherited as an autosomal codominant, also provides the opportunity to discuss classical Mendelian genetics. Further connections can be made to meiosis, gamete formation, and environmental influences that can affect phenotype. Lastly, sickle cell anemia provides an outstanding opportunity to build a connection between genetics and evolution. Students learn the mechanisms by which allele frequencies in a population change over time in response to selective forces (such as malaria) by using laboratory simulations and analyzing disease distribution data. In the Allele Frequencies and Sickle Cell Anemia Lab, students randomly draw red and white beans from "gene pool" containers to model the changes in b globin allele frequencies in a population in response to the selective pressure of malaria.

Genetics Concepts:
A number of genetics concepts are covered by State and National Standards. This unit addresses the following concepts:

Classical Genetics/Central Dogma:

• Genotype gives rise to phenotype.
• The two inherited alleles for a gene determine the phenotype for the trait.
• The DNA information provides instructions for building proteins.

Molecular Biology:

• The genetic information is encoded in DNA.

Evolution:

• Changes in DNA, or mutations, cause new alleles to arise, leading to variation among organisms within a population.

Applications:

• Genetics research has applications in many different fields.

Ethics:

• Genetics research raises many ethical, legal, and social issues.

References:

• *"Teaching Biology Around Themes: Teach Proteins and DNA Together," S. Offner, American Biology Teacher 54, #2 (1992).
• *"Making the Chromosome-Gene-Protein Connection," C. Mulvihill, American Biology Teacher 58, #6 (1996).
• *"Mystery of the Crooked Cell: An Investigation and Laboratory Activity About Sickle-Cell Anemia," D. A. DeRosa and B. L. Wolfe, American Biology Teacher 61, #2, 137-148.
• Slides of normal and sickled red blood cells. Order from Triarch Inc. (800-848-0810).
• Three-dimensional Hemoglobin on the Internet. (Requires the Chime plug-in.) http://info.bio.cmu.edu/Courses/BiochemMols/BuildBlocks/Hb.html.
• Blood is Life. 45 min. video. Order from Films for the Humanities & Sciences (800-257-5126).
• Children By Design. Video, Secret of Life series.
• New Choices, New Responsibilities: Ethical Issues in the Life Sciences. B. Jennings, K. Nolan, C. Campbell, S. Donnelley, E. Parens, L. Turner, E. DeVaro, 1997. Decision-making framework for bioethical issues.
  Note: a review of New Choices and ordering information can be found at: http://genetics-education-partnership.mbt.washington.edu/rev/resource_reviews/newch.html.
  A brief description of the decision making template can be found at: http://genetics-education-partnership.mbt.washington.edu/Cool/tools/ethics.html.

*Note: American Biology Teacher has agreed to send out reprints of these articles upon request. To contact ABT, visit their website at: http://www.nabt.org/publications_journals.html.

Contributed by Jeanne Ting Chowning, BioLab, Seattle, WA
Provided jointly by the GENETICS Project and the Genetics Education Partnership