Interpreting Pedigrees Activity 8 Interpreting Pedigrees

Read the introduction. (P. 316) What is a PEDIGREE?

A pedigree shows generations and relationships among biological parents and offspring. It also tracks which of those individuals have a specific trait.

What information can geneticists obtain by analyzing a pedigree? Challenge What information can geneticists obtain by analyzing a pedigree?

Analyzing Pedigrees Point out the features of pedigrees. Ask students, What can you say about the individuals shown in the pedigree? Have the class generate a list of ideas, and take this opportunity to gauge students’ understanding of pedigrees. As needed, review with students the symbols that represent biological parents, offspring, male, female, affected individuals, and generations. This image is from Transparency 8.1, “Analyzing Pedigrees.”

Pedigree A: Huntington’s Disease Looking at this pedigree… do you think Huntington’s Disease is a DOMINANT, RECESSIVE, or SEX-LINKED trait? How do you know? Students may need support in determining the correlation between the types of inheritance and the patterns seen on the pedigrees. Suggestions and more information can be found in the Teacher’s Edition for this activity. Once students have completed Procedure Step 5, discuss their conclusions about the inheritance of dominant, recessive, and sex-linked recessive traits, making sure students understand the patterns these types of traits demonstrate in pedigrees. Huntington’s Disease is a dominant trait. The pedigree supports this because the trait occurs in each generation and in both genders, although the evidence does not rule out a recessive trait.

Pedigree B: PKU Looking at this pedigree… do you think PKU Disease is a DOMINANT, RECESSIVE, or SEX-LINKED trait? How do you know? PKU (phenylketonuria) is a recessive trait. This is supported by the pedigree showing that it skips generations and is found in both genders.

Pedigree C: Hemophilia Looking at this pedigree… do you think Hemophilia is a DOMINANT, RECESSIVE, or SEX-LINKED trait? How do you know? Hemophilia is a sex-linked recessive trait. The pedigree shows that only sons of carriers express the condition. You may want to emphasize that only genetic testing identifies carriers of hemophilia, and that the evidence does not rule out a recessive trait. Once students have completed the rest of the Procedure Steps, hold a class discussion to review students’ conclusions about what kind of inheritance mechanism factor Z displays. More information on holding this class discussion can be found in the Teacher’s Edition for this activity.

Analysis 2 Examine the pedigree below for grain plants with a trait for a high amount of protein. What can you determine about the trait based on the pedigree? Analysis Question 2 is a Quick Check for you to monitor students’ understanding of pedigrees and the information they convey. See the Teacher’s Edition for this activity and Teacher Resources IV: Assessment for more information and a sample student response.

Analysis 3 How do farmers and agricultural geneticists use the information provided by a pedigree to breed desirable traits in an agricultural crop? Discuss students’ responses to Analysis Question 3 and how this information relates to the issue of genetically modified organisms. See the Teacher’s Edition for this activity for more information and a sample student response.

Analysis 4 On the next slide is a pedigree for cattle that have been genetically modified to produce a human protein that helps prevent blood clots in humans. Using the information in the pedigree, answer the following questions: What type of inheritance mechanism—dominant, recessive, or sex-lined recessive—is shown in the pedigree? Support your answer with evidence. From the information in the pedigree from generation 3, can you determine if the gene is still present in the cow population? Explain why or why not? Discuss students’ responses to Analysis Question 4 and how this information relates to the issue of genetically modified organisms. See the Teacher’s Edition for this activity for more information and a sample student response.

Analysis 4, continued Discuss students’ responses to Analysis Question 4 (Note: Question text is on previous slide.) and how this information relates to the issue of genetically modified organisms. See the Teacher’s Edition for this activity for more information and a sample student response.

What information can geneticists obtain by analyzing a pedigree? Revisit the Challenge What information can geneticists obtain by analyzing a pedigree? Students should be able to articulate that pedigrees allow scientists to trace traits over multiple generations within a family. They should also be able to explain how to analyze a pedigree to infer the genetic mechanism of inheritance for a given trait.

allele carrier Dominant pedigree recessive sex-linked Key Vocabulary allele carrier Dominant pedigree recessive sex-linked sex-linked recessive See Teacher Resources III: Literacy for more information on key vocabulary and the most effective strategies to enhance student vocabulary learning. Note that bold words are formally defined in this activity. Words in regular font are used in the activity, but not formally defined. The definition of a key vocabulary word should not be discussed as a class prior to the formal definition being introduced.