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Name________________________ Period_____ Date______ Lab #______ Regents Biology Genetic Disorders: Case Studies Genetic disorders are diseases that are caused by an abnormality or mutation in an individual’s DNA. Mutations in the DNA can range from a small, single base change to the addition or deletion of an entire chromosome. You can be born with these DNA mutations as a result of your mother or father, or both, passing on their mutations to you, if they are in your dad’s sperm and your mom’s egg. Mutations in your DNA can also arise later in life, possibly from environmental factors such as excessive alcohol consumption, smoking cigarettes or exposure to UV radiation from the sun. Define genetic disorders. How can a child be born with a genetic disorder? Other than being born with a DNA mutation, list three other factors in your environment that can cause mutations in your DNA. There are many types of mutations that can cause genetic disorders. A point mutation is when one nitrogenous base in the DNA is changed. Example of a Point Mutation: Original DNA: Mutated DNA: ATTACTATCGAGATTAT ATTACTATGGAGATTAT Use a highlighter to highlight or underline where the point mutation has occurred in the mutated DNA strand. Mutations can also occur when either a nitrogenous base is either added or deleted. The addition of an extra letter in a gene is called an addition. Deleting a nitrogenous base is called a deletion. Examples of Addition and Deletion Mutations: Original DNA: Mutated DNA #1: Mutated DNA #2: ATTACTATCGAGATTAT ATACTATCGAGATTAT ATTACTATCCGAGATTAT Which mutated DNA strand is an example of an addition mutation? __________ How do you know? Be as specific as possible. Mutations can be good, bad or have little effect on an organism. Changes in the DNA code do not always guarantee a change in the amino acid sequence or protein that is made. If the mutation does not change the sequence of amino acids then it will not change the type of protein being made and therefore, will have little to no effect on the organism. Some mutations can cause diseases such as Cystic Fibrosis, Breast Cancer, Sickle Cell Anemia, Downs Syndrome, or Tay Sach’s Disease. These diseases are examples of when the mutated DNA does cause a change in the amino acid sequence and therefore, a change in the protein being made. 1 Examples of Mutations Original DNA: Original RNA: Amino Acids: TAC AUG Start Mutated DNA #1: TAC Mutated RNA #1: ____ Mutated Amino Acids _____ GGG CCC Pro CGC GCG Ala TTT AAA Lys ATT UAA Stop GGC CGC TTC ATT _____ ____ ____ _____ _____ _____ ____ _____ In this example, did the amino acid sequence change? If so, describe what amino acid(s) changed. Did this mutation cause a change in the protein that was made by the DNA? Explain why or why not. Was this mutation harmful, beneficial or create no change in the person? Explain how you know. Original DNA: Original RNA: Amino Acids: TAC AUG Start Mutated DNA #2: TAC Mutated RNA #1: ____ Mutated Amino Acids _____ GGG CCC Pro CGC GCG Ala TTT AAA Lys ATT UAC Stop GGC AGC TTC ATT _____ ____ ____ _____ _____ _____ ____ _____ In this example, did the amino acid sequence change? If so, describe what amino acid(s) changed. Did this mutation cause a change in the protein that was made by the DNA? Explain why or why not. Was this mutation harmful, beneficial or create no change in the person? Explain how you know. 2 Case Study #1: Sickle Cell Anemia Directions. While watching the short video: “ Sickle Cell Anemia: A Patient’s Journey,” answer the following questions. 1. What disease does Alexandria have? 2. What cells are deformed in Alexandria’s body? 3. What happens to Sickle Cell patients’ red blood cells when they are flowing through her blood vessels? 4. What are some symptoms of the disease? 5. Why is Alexandria at risk for organ failure? 6. There is no cure for sickle cell anemia. What do doctors do to help keep patients as healthy as possible? 7. What is the purpose of the procedure that is used to keep patients healthy? 8. In your group, get a microscope and two blood smears: a prepared sample of Infinity’s blood and a blood smear of a normal individual. In the area below, sketch the appearance of Infinity’s red blood cells and a healthy patient’s red blood cells. Sickle Cell Patient’s Blood Smear Healthy Patient’s Blood Smear 3 10. Make an inference, how do you think the shape of the red blood cells in a sickle-cell patient may affect how well the cells are able to circulate throughout the blood vessels? 11. What body system is disrupted in Sickle-Cell Anemia patients?________________________ 12. Below is a table, comparing the gene mutation that occurred in Infinity’s DNA for making hemoglobin and the gene for a healthy individual. Complete the mRNA, the amino acid and shape of red blood cell rows. DNA Code Normal Hemoglobin Sickle Hemoglobin GGG CTA CTT TTT GGG CAA CTT TTT mRNA Code Amino Acid Order Shape of Red Blood Cells Sickle Cell Anemia is a genetic disease caused by one single base mutation in the DNA. This disease is recessive, meaning that carriers of the disease do not have symptoms. Therefore, a seemingly normal couple may have a child with sickle cell anemia. Complete the punnett squares below to determine the odds of having a child with sickle cell anemia. Sickle Cell Trait = s Normal Trait = S 13. Complete the punnett square to determine the likelihood of two parents, each heterozygous for the disease, having a child with sickle cell anemia. ____ % of offspring would have sickle-cell anemia ____% of offspring would not have sickle cell anemia, but would be carriers for the disease. ____% of offspring would not have sickle cell anemia and would not be carriers for the disease. 14. Complete the punnett square to determine the likelihood of two parents, one who is a carrier of the sickle cell trait and one who is homozygous dominant (normal), having a child with sickle cell anemia. ____ % of offspring would have sickle-cell anemia ____% of offspring would not have sickle cell anemia, but would be carriers for the disease. ____% of offspring would not have sickle cell anemia and would not be carriers for the disease. 4 Case Study #2: Tay Sach’s Disease Watch the following video about Hayden, a young boy with Tay Sach’s Disease. http://www.pbs.org/wgbh/nova/genome/program.html Click on the “One Wrong Letter” link. 1. What were some of the early warning signs that Hayden’s parents noticed by the time he was a year old, indicating there was something wrong with him? a. ______________________________________________________________________ b. ______________________________________________________________________ c. ______________________________________________________________________ 2. What major organ is affected by children with Tay Sach’s disease?_____________________ 3. What major body system is affected? _______________________ 4. How many mistakes in the DNA code are there for children with Tay Sach’s disease?______ 5. Gene’s (segments of DNA) create_________________. 6. Tay Sach’s patients are missing an important protein in their body that is created by a specific sequence of DNA. What is the job of this protein normally?__________________________ ___________________________________________________________________________ 7. How does all of this extra fat building up in the brain affect the child’s brain cells? ___________________________________________________________________________ 8. Is there a cure for Tay Sach’s disease?___________ What is the life expectancy of children with Tay Sach’s disease?______________________________________________________ 9. Both parents of Hayden were carriers of the tay-sach’s disease. What does this mean? Did they have the disease? How did Hayden end up with the disease? ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ 10. What ended up happening to Hayden?___________________________________________ 11. Complete the following Punnett square to determine if both parents were carriers of the TaySach’s disease trait, what is the likelihood that they will have a child who actually has the disease. Mom T= Normal Gene (segment of DNA) t= Tay Sach’s Gene (segment of DNA) a. What is the probability that they will have a child with Tay Sach’s Disease? ______________ Dad b.What is the probability that they will have a child who is a carrier for the Tay Sach’s trait?____________ 5 Sickle Cell Anemia BOTH Tay- Sach’s Disease 6 HUNTINGTON DISEASE FAMILY SECRETS UNIVERISTY OF ROCHESTER 7