Decoding Inheritance: Pedigree Analysis of Sex-Linked Recessive Traits
Lesson Description
Video Resource
Pedigree for determining probability of exhibiting sex linked recessive trait | Khan Academy
Khan Academy
Key Concepts
- Pedigree Charts
- Sex-Linked Inheritance
- Recessive Traits
- Probability Calculation
- Genotype and Phenotype
Learning Objectives
- Students will be able to define and interpret symbols used in pedigree charts.
- Students will be able to explain the mechanism of sex-linked recessive inheritance.
- Students will be able to determine the genotypes of individuals in a pedigree.
- Students will be able to calculate the probability of offspring inheriting a sex-linked recessive trait using pedigree analysis.
Educator Instructions
- Introduction (5 mins)
Briefly introduce pedigree charts as tools for tracking traits through generations. Discuss the concepts of sex-linked inheritance and recessive traits as a review. Mention that the class will use a Khan Academy video to learn how to solve probability questions using pedigrees. - Video Viewing (10 mins)
Play the Khan Academy video: 'Pedigree for determining probability of exhibiting sex linked recessive trait'. Instruct students to take notes on key terms, symbols, and problem-solving strategies presented in the video. - Guided Practice (15 mins)
Work through one or two example pedigree problems together as a class, modeling the thought process and calculations. Emphasize the importance of correctly identifying genotypes and phenotypes. - Independent Practice (15 mins)
Provide students with additional pedigree problems to solve individually or in small groups. Circulate to provide assistance and answer questions. - Wrap-up and Discussion (5 mins)
Review key concepts and address any remaining student questions. Preview upcoming topics related to genetics.
Interactive Exercises
- Pedigree Construction
Have students create their own simplified pedigree charts based on fictional families with a sex-linked recessive trait. They should then exchange pedigrees and determine the probability of a particular individual inheriting the trait. - Online Pedigree Simulation
Use an online simulation tool (if available) that allows students to manipulate pedigree charts and observe the resulting probabilities of trait inheritance.
Discussion Questions
- How does sex-linked inheritance differ from autosomal inheritance?
- Why are males more likely to express sex-linked recessive traits than females?
- What are some real-world examples of sex-linked recessive disorders?
- How can pedigree analysis be used in genetic counseling?
Skills Developed
- Critical Thinking
- Problem Solving
- Data Interpretation
- Scientific Reasoning
- Application of Mathematical Concepts
Multiple Choice Questions
Question 1:
In a pedigree chart, what shape represents a male?
Correct Answer: Square
Question 2:
What does a shaded shape in a pedigree chart typically indicate?
Correct Answer: Affected individual
Question 3:
Sex-linked traits are typically located on which chromosome?
Correct Answer: X Chromosome
Question 4:
A female with one copy of a recessive X-linked allele is referred to as a:
Correct Answer: Carrier
Question 5:
If a colorblind (X-linked recessive) father has children with a woman who is not a carrier, what percentage of their sons will be colorblind?
Correct Answer: 0%
Question 6:
Which of the following is NOT typically found in a pedigree?
Correct Answer: Individuals' names
Question 7:
What is the probability of two parents, both carriers for an X-linked recessive trait, having an affected son?
Correct Answer: 50%
Question 8:
In pedigree analysis, determining the _______ of individuals is crucial to understanding inheritance patterns.
Correct Answer: Genotype
Question 9:
A horizontal line connecting a male and female in a pedigree represents:
Correct Answer: Marriage/Mating
Question 10:
Why are X-linked recessive traits more commonly expressed in males than females?
Correct Answer: Males have only one X chromosome
Fill in the Blank Questions
Question 1:
A chart used to trace the inheritance of traits across generations is called a __________.
Correct Answer: pedigree
Question 2:
A trait that is expressed only when an individual has two copies of the responsible allele is called _________.
Correct Answer: recessive
Question 3:
A female who carries one copy of a recessive X-linked allele but does not express the trait is called a _________.
Correct Answer: carrier
Question 4:
Sex-linked traits are located on the sex chromosomes, usually the ____ chromosome.
Correct Answer: X
Question 5:
If both parents are carriers for a recessive trait, the probability of their child inheriting the trait is _____%
Correct Answer: 25
Question 6:
In a pedigree chart, a ________ represents a female.
Correct Answer: circle
Question 7:
Individuals exhibiting the trait of interest are typically represented by _________ shapes in a pedigree.
Correct Answer: shaded
Question 8:
The genetic makeup of an individual is known as their _________.
Correct Answer: genotype
Question 9:
The observable characteristics of an individual are known as their _________.
Correct Answer: phenotype
Question 10:
A person that has one affected allele and one unaffected allele for a trait is considered to be ________.
Correct Answer: heterozygous
Educational Standards
Teaching Materials
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