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Project 8.2.7 Mystery Disease Part 2: Genetic Testing Introduction At the conclusion of the previous assignment, you determined that the patient, Joe Bloggs, should be tested for Huntington’s disease based on family history and the patient’s symptoms. Huntington’s disease is an inherited disease that is caused by a mutation in the DNA of the affected person. DNA, or deoxyribonucleic acid, is a molecule located in the nucleus of the cell that determines the structure of proteins produced in the cell. This genetic information is inherited, or passed from parent to child, with half of the child’s DNA coming from each parent. A person with Huntington’s disease has a mutation or change in their DNA that causes a mutation in the resulting protein. To confirm a diagnosis of Huntington’s disease, a genetic test is performed that identifies if the person has the mutation in his or her DNA. DNA must be isolated from the rest of the cell before genetic testing can occur. This chemical process involves collecting the cells, dissolving the cell membrane, and gathering the DNA molecules together. Once the DNA has been isolated, it can undergo a variety of different genetic tests. In this project you will learn more about Huntington’s disease and investigate how DNA is isolated for genetic testing by collecting your cheek cells, isolating DNA, and creating a necklace with your isolated DNA. Equipment Laboratory Journal Pencil Computer with Internet access Medical History Form from 8.2.6 Carolina DNA Necklace Kit Small plastic cup with 2 mL of sport drink 15-mL tube Plastic pipet Pendant tube Piece of embroidery thread Lysis solution Ice cold 70% ethanol Safety goggles Latex or nitrile gloves Permanent marker © 2013 Project Lead The Way, Inc. PLTW Gateway – Medical Detectives Project 8.2.7 Mystery Disease Genetic Testing – Page 1 Procedure What is Huntington’s Disease? 1. As a class or individually, watch the video titled “What is Huntington’s Disease?” at http://hopes.stanford.edu. 2. Visit the page on the HOPES website titled “Bryan’s Dad has Huntington’s Disease” and read through Part I. https://www.stanford.edu/group/hopes/cgibin/wordpress/2010/07/bryans-dad-has-huntingtons-disease/ As you read, answer conclusion questions 1-8. 3. As time allows, investigate Huntington’s disease on the HOPES website. How is DNA isolated? DNA is often described as the “code of life” because it determines an organism’s characteristics and is passed from one generation to the next. DNA is located in almost every cell of your body. The length of DNA is about 100,000 times as long as the cell itself. However, it fits into the nucleus, which takes up only about 10% of the cell’s volume by folding around proteins and compacting into chromosomes. Answer the questions below as your teacher reviews the structure of DNA. 1. What are the base pairs? 2. What molecule is encoded by genes? 3. Describe the basic structure of DNA. 4. What is a histone? 5. How many chromosomes do human beings have? 6. Label the image below: © 2013 Project Lead The Way, Inc. PLTW Gateway – Medical Detectives Project 8.2.7 Mystery Disease Genetic Testing – Page 2 7. Describe the three steps involved in precipitating and isolating DNA from cheek cells as your teacher continues the presentation. a. Collect cheek cells b. Cell lysis c. DNA precipitation 8. What is the importance of DNA extraction? © 2013 Project Lead The Way, Inc. PLTW Gateway – Medical Detectives Project 8.2.7 Mystery Disease Genetic Testing – Page 3 Follow the directions below to extract and isolate the DNA from your cheek cells. 4. Obtain the DNA Necklace Instructions handout and workstation supplies. 5. Follow the directions on the DNA Necklace Instruction handout to complete the experiment. 6. After you have created your DNA necklace, either take a photo of the DNA in the vial or draw a picture of your observations. 7. While you are waiting for the DNA to precipitate out of the lysate solution, answer conclusion questions 9-11 from the inherited diseases presentation. 8. Answer remaining conclusion questions. Conclusion 1. According to the story, what symptoms typical of HD did Bryan’s dad display? 2. How old is Bryan’s dad now and how old was he when his mother died from Huntington’s disease? 3. Why are the chances of inheriting Huntington’s disease like flipping a coin? 4. What cells are damaged in Huntington’s disease and where in the brain are they located? 5. What gene on Bryan’s dad’s DNA is mutated? 6. Would you expect Bryan’s dad to have more or less than 40 codons of CAG in his Huntington gene? Why? 7. How does the huntingtin protein damage cells? 8. How is Huntington’s disease confirmed? © 2013 Project Lead The Way, Inc. PLTW Gateway – Medical Detectives Project 8.2.7 Mystery Disease Genetic Testing – Page 4 9. Explain how a recessive genetic disease is inherited. 10. Explain how a dominant genetic disease is inherited. 11. Is Huntington’s disease a recessive or dominant genetic disease? 12. Were you able to see the double helix structure of the DNA that condensed in the vial? Why or why not? 13. What percent chance does the teenage daughter of the patient have of getting Huntington’s disease? 14. Would you recommend that the daughter be tested for the HD mutation? Why or why not? © 2013 Project Lead The Way, Inc. PLTW Gateway – Medical Detectives Project 8.2.7 Mystery Disease Genetic Testing – Page 5