Its All in the Family Tree That Is (Developing a Pedigree) Concept Development

Transcription

1 Its All in the Family Tree That Is (Developing a Pedigree) Concept Development Problem: How can you set up a pedigree, given a family history? Materials: handout of commonly used pedigree symbols Background: Looking at the genetic history of a family is the primary job of a genetic counselor. This history is the main tool a geneticist has to determine inheritance patterns within a family. As information is gathered about the family, the geneticist places it on a document called a pedigree. A human pedigree helps to keep track of relationships and traits within the family. It is useful in helping families identify the risk for transmitting a number of inherited illnesses. A pedigree is drawn using shapes connected by horizontal and vertical lines. Vertical lines represent generations. Horizontal lines connect parents with each other, and siblings with each other. Males are indicated by a square, and females are shown with a circle. A diamond is used to identify individuals of unknown sex. A pedigree reflects only one trait, but families may have several pedigrees. Each individual listed on your pedigree should be identified with a number. Generally the first person on the left side of each generation begins with the number one. Each generation is identified with a Roman numeral. The oldest generation would carry the Roman numeral I. An individual who is a carrier of the gene in question, but who does not express its characteristics, is drawn as a half colored in shape. If an individual expresses the phenotypic characteristics of the disorder, their shape is fully colored. Let s Investigate: Read the following three scenarios, presented as conditions. Create a pedigree to show each condition outlined. Put each pedigree on a separate piece of paper. Marcy and Dale Rice have a son, Mark, and a daughter, Lisa. Both children are healthy and appear normal. Marcy and Dale s neighbors, Tim and Cheryl Binton also have a son, James, and have two daughters, Carrie and Janet. James, Carrie, and Janet have always been healthy. As they grew up all five children played together often, and became good friends. Lisa and James began dating in high school and following their college graduation, were married. They now have three children. Their son, Terry, and one daughter, Kelly, have albinism. Their other daughter, Bethany, has normal skin pigmentation. Condition # Late in the afternoon,, September 1, 1997, Jacob Ward, Sam Beldon, Ken Maynard, Tim Deckland, and Paul Wilmand were enjoying a rousing game of basketball. Little did they know that within the hour one of them would be dead. After hitting his third threepointer of the game, Ken suddenly fell to the ground, clutching his chest. The paramedics were called, but Ken died within the hour of heart failure. The physician conducting the autopsy used both the family history and microscopic examination of Ken s heart muscle to diagnose familial hyperthrophic cardiomyopathy. This disorder affects both sexes and doesn t skip generations. Ken s father, Jeff, died at a young age of heart failure, as had two of his sisters, Mary and Kim. Jeff s other sister, Susan, married Sam, and neither of them are 61

2 affected. Jeff s brother, Raymond, is also not affected. Following the diagnosis, blood cells were taken from Ken s siblings, Sarah and Eric, and two cousins, Liza and Ben. All were tested for the gene. Liza and Ben s mother, Kim, had the condition. Kim s husband, Jake, however, was unaffected. Liza was diagnosed with the condition. She was told that, even though she was still healthy, restricting her exercise to swimming might extend her life. Ken s paternal grandfather, Jerry, and a paternal great-uncle, Kendal, had the disorder. Jerry s wife, Pearl, and his sister, Mabel were unaffected. Condition # 3 Michael was an active toddler. He was an only child, but that didn t stop him. He was full of energy. He bounded from room to room when inside and ran circles around the house when outside. As Michael grew he became more and more excited about going to school. At last it was time, and at age 6 Michael started school. As the year progressed, Michael came home with more and more bruises. His teachers commented that he seemed to have lost his coordination. He was falling down a lot. Time progressed and Michael didn t get any better. His mother, June, took him to the doctor. Michael was tested, and had a high level of creatinine phosphokinase in his cells. He was diagnosed with Duchenne Muscular Dystrophy. Michael s parents were surprised because neither one of them had the condition. Both of Michael s parents came from small families. June had one brother, Ted, and one sister, Tina. Ted had muscular dystrophy. Bill, Michael s, father, also had one brother, and two sisters, Paul, Mary, and Laura. Harriet, June s mother, was thought to have a mild form of some muscle defect. Michael s cousin, Robert, also has muscular dystrophy. He is the sson of June s sister, Mary and her husband Kyle s. June and Bill don t know of anyone else in the family who has symptoms such as these. They had heard that June s mother, had a brother, Marcus, who spent his life in a wheelchair. Bill s parents, Sophie and Charles, did not have the condition. Neither did Harriet s husband, Lyle. Summing Up: 1. Name the inheritance pattern described in condition #1?. Do men and women have the capability to transmit this condition equally? 3. List the people who are certain carriers of this condition. 4. List the family members possessing the phenotypic characteristics of the condition. 5. Can you identify anyone who will NOT be a carrier of the gene? Who? How can you tell? Condition # 6. Name the inheritance pattern described in condition #? 7. Do men and women have the capability to transmit this condition equally? 8. List the people who are certain carriers of this condition. 9. List the family members possessing the phenotypic characteristics of the condition. 10. Can you identify anyone who will NOT be a carrier of the gene? Who? How can you tell? 11. Name the inheritance pattern described in condition # 3? 1. Do men and women have the capability to transmit this condition equally? 13. List the people who are certain carriers of this condition. 14. List the family members possessing the phenotypic characteristics of the condition. 15. Can you identify anyone who will NOT be a carrier of the gene? Who? How can you tell? 6

3 Teacher Notes Its All in the Family Tree That Is (Developing a Pedigree) Concept Development BIOMES Topic: Genetics Patterns of Inheritance Lab setup: none easy moderate difficult Class time required: minutes minutes minutes minutes Reasoning level: easy moderate difficult Process skills: observing classifying inferring predicting interpreting data formulating models Web Connect: yes no Objectives: Students will interpret data to determine the family pedigrees of a number of reallife families. National Science Education Standards: Content Standards: Life Science - The cell, Molecular basis of heredity Matter, energy and organization in living systems Science as Inquiry: Abilities necessary to do scientific inquiry Science in Personal and Social Perspectives: Personal and community health Materials: Notebook paper or typing paper Handout of commonly used pedigree symbols. Teaching Strategies: The students should have been introduced to the autosomal dominant, autosomal recessive, and sex-linked inheritance patterns before completing this activity. Having learned about dominant and recessive traits allows the student to focus on how a pedigree is constructed. Remind the students that the easiest way to begin a pedigree is with a family tree. When they have the family tree diagramed, they can add the correct symbols. Sample Data: I-1 Marcy II-1 Mark III-1 Terry I- Dale II- Lisa III- Bethany I-3 Cheryl II-3 James III-3 Kelly I-4 Tim II-4 Carrie II-5 Janet 63

4 Condition # I-1 Pearl II-1 Jeff III-1 Ken I- Jerry II- Amber III- Sarah I-3Kendal II-3 Susan III-3 Eric I-4 Mabel II-4 Sam III-4 Liza II-5 Mary III-5 Ben II-6 Raymond II-7 Kim II-8 Jake II I III I-1 Charles II-1 Laura III-1 Michael I- Sophie II- Mary III- Robert I-3 Lyle II-3 Paul I-4 Harriet II-4 Bill I-5 Marcus II-5 June II-6 Ted II-7Tina II-8 Kyle Sample Answers to Summing Up: 1. The inheritance pattern is autosomal recessive, and doesn t show up until the third generation.. Men and women can transmit this condition equally. 3. Lisa and James are certain carriers, but Marcy, Dale, Cheryl, and Tim are also likely carriers. 4. Terry and Kelly have the phenotypic characteristics of Albinism. 5. Anyone in either family could be a carrier, because the gene was passed down from Marcy, Dale, Cheryl, and Tim. Some of the individuals have not yet married and do not have children so it is unclear what they will pass on. 64

5 Condition # 6. This family expresses an autosomal dominant inheritance pattern. 7. Men and women can pass on this gene equally. 8. Jerry, Kendal, Jeff, Mary, Kim, Ken, and Lisa are carrier of the condition. Since the disorder is expressed as a dominant trait, all carriers also have the phenotypic characteristics of the disorder. 9. Jerry, Kendal, Jeff, Mary, Kim, Ken, and Lisa all possess the pheonotypic characteristics of the disorder. 10. Anyone who has the gene will also have the disorder, because it expressed as a dominant trait. Carriers will have the disorder. 11. The inheritance pattern is sex-linked, on the X-chromosome. 1. Women have two X chromosomes so are twice as likely to pass on the affected chromosome. 13. The carriers are Harriet, June, and Mary. 14. The people showing phenotypic characteristics of this condition are Marcus, Ted, Robert, and Michael. 15. None of Michael s dad s relatives, and the males without MD who are related to June, Michael s mother, will be carriers. 65