Students will learn the names, characteristics, and causes of several different sex linked disorders, including muscular dystrophy. Students will create, describe and predict genotypes according to genetic pedigrees.
Additional Learning Outcomes
Students will be introduced to the ideas of genetic engineering and genetic counseling.
Students will need access to the Internet to complete research on a sex-linked chromosomal disorder.
2 hours, 50 minutes
Step 1 Duration: Varies Teacher Preparation
Review the lecture notes in Step 2 to become familiar with the concepts and assure that it is at the right level for the students. Students need prior knowledge of genetics terminology like dominant, recessive, carrier, sex-linked, as well as familiarity with pedigree symbols. A complete list is included in the “Genetics Terminology Word List”. If they are not familiar with genetics terms, please use the “Definitions for Sex-linked Disorder Vocabulary” to help acquaint them. Additionally, a key to pedigree symbols is included in the “Pedigree Symbols” document for the students to review if needed. Both the vocabulary sheet and the pedigree symbols document can be passed out before the lecture. Refer to the Web resources below for additional information about genetics terminology and pedigree symbols.
Title: Basic Principles of Genetics
URL:http://anthro.palomar.edu/mendel/Default.htm Description: This is a tutorial Web site on the basics of genetics. This site includes vocabulary with definitions as well as links to other related information.
Title: Pedigree symbols and Genetic Terms
URL:http://www.people.virginia.edu/~rjh9u/pedsymb.html Description: This Web site contains some additional pedigree symbols and genetic terms with definitions. It includes symbols for twins and still births.
Title: Pedigree symbols, rules, guidelines and examples
URL:http://wwwrhjh.lkwash.wednet.edu/homehelp/familytree/ Description: This Web site contains pedigree symbols, rules, guidelines and examples. In addition, this site provides directions on how to create a family pedigree.
Title: Genetics Terminology Word List
File Name:Sex linked disorders word list.doc Description: This document contains a list of genetic terminology that students should be familiar with before continuing this lesson.
Title: Definitions for Sex-linked Disorder Vocabulary
File Name:Sex-linked word definitions.doc Description: This documents provides brief and easy to understand definitions to the vocabulary for sex-linked disorders.
Title: Pedigree Symbols
File Name:Pedigree Symbols.doc Description: This Word document contains some commonly used pedigree symbols. Additional symbols can be found in the Web resources.
Step 2 Duration: 55 minutes
Notes on Sex-Linked Genes and Inheritance
In this step, students will learn about sex-linked genes, sex chromosomes and inheritance using the “Lecture Notes for Sex-Linked Disorders” provided as a supplemental document. This lecture will begin with a general discussion about genes, chromosomes, and inheritance and then will move on to sex-linked genes, followed by sex chromosomes. Please go through the lecture notes carefully and conclude by answering any questions about the material covered. The Web resources provide additional information on genetic counseling.
Title: Genetic counseling
URL:http://www.accessexcellence.org/AE/AEC/CC/counseling_background.html Description: This National Health Museum Web site contains information on genetic counseling.
Title: Frequently Asked Questions about Genetic Counselors and the National Society of Genetic Counselors
URL:http://www.nsgc.org/consumer/faq_consumers.asp Description: This National Society of Genetic Counselors Web site contains frequently asked questions and answers about genetic counseling.
Title: Lecture Notes for Sex-Linked Disorders
File Name:Lecture Notes.doc Description: These lecture notes discuss the genetics of sex-linked genes and sex chromosomes.
Step 3 Duration: 15 minutes Pedigree Practice
Using what the students have just learned from the lecture notes, they will answer questions in the “Pedigree Practice Sheet” included as a supplemental document. The students should work in groups or individually, but should be brought back together for discussion of the pedigree charts when they have completed them. Use the “Pedigree Practice Answer Key” to check for accuracy and to facilitate this discussion.
Title: Pedigree Practice Sheet
File Name:Pedigree Practice Sheet.doc Description: Word problems that allow the students to create three different pedigrees and answer a question about each of them.
Title: Pedigree Practice Answer Key
File Name:Pedigree Practice Answer Key.doc Description: Answer key with pedigrees drawn out and answers to the questions posed on the pedigree practice sheet.
Step 4 Duration: 20 minutes
Discussion and Summarization
After the students have completed their pedigrees, have them review additional concepts through the “What Disorder Am I?” game. In this game the students will divide into teams and quiz each other on important concepts and disorders discussed in the lecture notes. The directions are included in the “What Disorder Am I?” document and the cards for the game are included in the “Cards for ‘What Disorder Am I?’ Game” document. After the students have finished the game, bring the students back together as a group and ask them to describe some types and characteristics of muscular dystrophy. This discussion will lead them into the research they will be conducting on muscular dystrophy in the following step.
Title: What Disorder Am I?
File Name:Lecture Review Game - Directions.docDescription: This document includes directions for a game to review the information presented in the “Lecture Notes for Sex-Linked Disorders” in Step 2. In addition, the game serves as a lead in to the muscular dystrophy research students will conduct in Step 5.
Title: “Cards for ‘What Disorder Am I?’ Game”
File Name:Cards for Lecture Notes Game.doc Description: This document contains game cards for the “What Disorder Am I?” game.
Step 5 Duration: 1 hour, 20 minutes
Research and Presentation
Group the students into groups of two. Assign the group a research topic, one of the types of muscular dystrophy from the “Lecture Notes for Sex-Linked Disorders” in Step 2. Ask the students to break up the questions listed in the “Muscular Dystrophy Research Guidelines” included as a supplemental document in this step. An example of answers to these questions is provided in the “Research Answer Key”. Once all of the questions have been researched and answered, create a story board. The storyboards need to be on either a tri-fold board or a piece of poster board. See the “Display Board Rubric” for the information the storyboard should contain. After all students have finished their boards, have the students present their information to the class.
Title: Muscular Dystrophy Association Web site
URL:http://www.mdausa.org/ Description: This Muscular Dystrophy Association (MDA) Web site contains links to the different types/forms of the muscular dystrophy.
Title: Becker Muscular Dystrophy
URL:http://www.mdausa.org/disease/bmd.cfm Description: This MDA Web site provides information on Becker muscular dystrophy. In addition, this site contains links that students should be encouraged to explore.
Title: Ducheene Muscular Dystroyphy Web Site
URL:http://www.mdausa.org/disease/dmd.cfmDescription: This MDA Web site provides information on Duchenne muscular dystrophy. In addition, this site contains links that students should be encouraged to explore.
Title: Emery-Dreifuss Muscular Dystrophy Web Site
URL:http://www.mdausa.org/disease/edmd.cfm Description: This MDA Web site provides information on Emery-Dreifuss muscular dystrophy. In addition, this site contains links that students should be encouraged to explore.
Title: Muscular Dystrophy Association Diseases Page
URL:http://www.mdausa.org/disease/index.html Description: This Web site is the start of MDA’s diseases page. It contains links to many of the types of muscular dystrophy with information that could be included on the poster boards.
Title: Facts About Duchenne and Becker Muscular Dystrophies
URL:http://www.mdausa.org/publications/fa-dmdbmd-what.html Description: This MDA Web site contains information on Duchenne and Becker muscular dystrophies, two common types.
Title: National Instutute of Neurolocial Disorder and Stroke’s Muscular Dystrophy Information Page
URL:http://www.ninds.nih.gov/disorders/md/md.htm Description: This National Institutes of Health Web site contains basic information on muscular dystrophy. Also, it includes information on several of the different types of muscular dystrophy.
Title: Muscular Dystrophy Research Guidelines
File Name:Muscular Dystrophy Research Guidelines.doc Description: These research guidelines provide a set of questions for students to answer while doing their research on their type of muscular dystrophy.
Title: Research Answer Key
File Name:Muscular Dystrophy Research Guidelines Answer Key.doc
Description: This document includes possible answers to the “Muscular Dystrophy Research Guidelines” questions for Duchenne muscular dystrophy.
Title: Display Board Rubric
File Name:SexLinked ChromDisorder- Rubric.doc Description: This rubric provides guidelines for scoring storyboard project. It can be used for student self-assessment as well as teacher assessment.
Assessment Students will be assessed on their creation of pedigrees in Step 3 using the “Pedigree Practice Answer Key” and on their generation of a sex-linked disorder display board using the “Display Board Rubric” in Step 5.
Further Internet research on other types of sex-linked disorders with interested students could be facilitated. Additionally, a guest speaker from a local support group or a special education teacher could speak to the class about disability and health.
Title: Genetic Pedigrees
URL:http://www.msu.edu/~langley6/chs/Bio/Genetics/Peddirect.htm Description: This is a Web site that students can use to generate family pedigree. It provides a great for extra credit.
National Science Education Standards
LIFE SCIENCE, CONTENT STANDARD C:
As a result of their activities in grades 9-12, all students should develop understanding of
autosomes and sex chromosomes segregate during meiosis (review meiosis if necessary)
sex of offspring is determined by the combination of sex chromosomes in the fertilized egg. The mother can only contribute an X chromosome because her genotype is XX, however the father can contribute either an X or a Y, because his genotype is XY. Therefore, the genotype of the off-spring is either male or female depending on whether the gamete receives an X or Y from the father.
Most organisms: XX=female XY=male
- The sex of some animals is determined in different ways.
Grasshoppers XX=girl XO=male
Ants and bees have NO sex chromosomes—sex determined by total chromosome number.
Fish and reptiles-sex determined by factors in the environment—like the temperature
A gene that is located on the X or Y chromosomes
Sex-linked gene examples:
White-eyes in fruit flies: If a fruit fly is white-eyed, then it must be male because the gene that makes the color of the eyes white is located on the Y chromosome. White eyes in fruit flies is a Y-linked trait..
Muscular dystrophy: Characterized by progressive weakness and degeneration of the skeletal and voluntary muscles with control movement
Affects people of all ages
Different forms have different onset ages, ranges from infancy to middle age or later
Duchenne Muscular Dystrophy, with an onset of 2 to 4 years, (X-linked)
Becker Muscular Dystrophy, with an onset in the teen and young adult years, (X-linked)
Emery-Dreifuss Muscular Dystrophy, with an onset of childhood or adulthood, (X-linked or autosomal)
Note: there are other forms of muscular dystrophy that are autosomal instead of X-linked
Hairy ears in humans: The gene for hairy ears is found only on the Y chromosome (Y-linked). Therefore, males are the only ones to have this sex-linked gene.
Below is an example of a pedigree for a Y-linked gene.
Color-blindness in humans: The gene for color blindness is located on the X chromosomes (X-linked) and is recessive. This means that color blindness affects more males than females because males only get one X chromosome while females get two X chromosomes. If a female has the gene for color blindness on one of her X chromosomes, it is likely that she will have the dominant gene on her other X chromosome and therefore will not express the trait. On the other, if a male has the gene for color blindness he does not have a second gene that could be dominant, so he will express the trait.
Hemophilia in humans: Like color-blindness, the gene for hemophilia is recessive and located on the X chromosome (X-linked). This means that males are more likely to be affected than females as explained above.
Historically, hemophilia has had an interesting effect on Queen Victoria and her family. She possessed the X-linked gene for hemophilia and passed this gene on to her children. This gene was passed down the royal family line, eventually affecting the youngest son of Tsar Nicolas the II, who received the gene from his mother, the granddaughter of Queen Victoria.