Decoding Inheritance: Sex-Linked Traits and Punnett Squares
Lesson Description
Video Resource
Example punnet square for sex-linked recessive trait | High school biology | Khan Academy
Khan Academy
Key Concepts
- Sex-linked inheritance
- Recessive traits
- Punnett squares
- Genotype vs. phenotype
- Carrier status
Learning Objectives
- Students will be able to define sex-linked recessive inheritance.
- Students will be able to construct a Punnett square for a sex-linked trait.
- Students will be able to calculate the probability of offspring inheriting a sex-linked recessive trait.
- Students will be able to differentiate between genotype and phenotype in the context of sex-linked traits.
- Students will be able to explain the concept of a 'carrier' for a recessive trait.
Educator Instructions
- Introduction (5 mins)
Briefly introduce the concept of sex-linked traits and their difference from autosomal traits. Ask students if they have heard of hemophilia and its inheritance patterns. Explain that the lesson will focus on using Punnett squares to predict the inheritance of a sex-linked recessive trait like hemophilia. - Video Viewing (10 mins)
Play the Khan Academy video: 'Example punnet square for sex-linked recessive trait'. Instruct students to take notes on the key terms and the steps involved in creating and interpreting the Punnett square. - Guided Practice (15 mins)
Work through a similar example problem on the board, guiding students through each step: identifying genotypes, setting up the Punnett square, and calculating probabilities. Emphasize the importance of correctly representing sex chromosomes (XX and XY) and alleles (H and h). Use the example from the video's transcript. - Independent Practice (15 mins)
Provide students with practice problems to solve individually or in pairs. These problems should involve different scenarios of sex-linked recessive inheritance, allowing them to apply the concepts learned. - Wrap-up & Review (5 mins)
Review the key concepts and address any remaining questions. Briefly introduce the concept of other sex-linked traits (e.g., color blindness) and their inheritance patterns.
Interactive Exercises
- Punnett Square Challenge
Divide students into groups and provide each group with a different scenario involving a sex-linked recessive trait. Each group must create a Punnett square and present their findings to the class. - Online Simulation
Use an online Punnett square simulator to explore different inheritance scenarios and visualize the resulting probabilities. Many free simulators are available online that allow students to manipulate parental genotypes and observe offspring phenotypes.
Discussion Questions
- How does the inheritance pattern of a sex-linked trait differ from that of an autosomal trait?
- Why are males more likely to express sex-linked recessive traits than females?
- What are the ethical considerations surrounding genetic testing for sex-linked disorders?
- How can understanding inheritance patterns help families make informed decisions about family planning?
Skills Developed
- Problem-solving
- Critical thinking
- Data analysis
- Scientific reasoning
- Model building
Multiple Choice Questions
Question 1:
A woman who is a carrier for hemophilia has a child with a man who does not have hemophilia. What is the probability that their son will have hemophilia?
Correct Answer: 50%
Question 2:
Which of the following genotypes represents a female carrier for a sex-linked recessive trait?
Correct Answer: XHXh
Question 3:
In a Punnett square for a sex-linked trait, what do the letters 'X' and 'Y' represent?
Correct Answer: Sex chromosomes
Question 4:
Hemophilia is caused by a:
Correct Answer: X-linked recessive allele
Question 5:
What is the probability of a daughter inheriting hemophilia if her father has hemophilia and her mother is a carrier?
Correct Answer: 50%
Question 6:
A male inherits his X chromosome from his:
Correct Answer: Mother
Question 7:
What does it mean to be a 'carrier' for a recessive trait?
Correct Answer: Having one copy of the recessive allele and not expressing the trait
Question 8:
Which of the following is NOT a characteristic of X-linked recessive inheritance?
Correct Answer: Affected fathers pass the trait to all their sons
Question 9:
A man with hemophilia has a child with a woman who is not a carrier. What is the probability that their daughter will be a carrier for hemophilia?
Correct Answer: 100%
Question 10:
The Punnett square is used to determine the:
Correct Answer: Possible genotypes of the offspring
Fill in the Blank Questions
Question 1:
Hemophilia is a blood clotting disorder caused by an _________-linked recessive trait.
Correct Answer: X
Question 2:
A person with hemophilia has trouble with their blood _________.
Correct Answer: clotting
Question 3:
Females have _______ X chromosomes.
Correct Answer: two
Question 4:
Males have _______ X chromosome and _______ Y chromosome.
Correct Answer: one
Question 5:
A _________ is someone who does not show a trait, but carries one of the alleles
Correct Answer: carrier
Question 6:
The dominant allele is shown with a _________ letter.
Correct Answer: capital
Question 7:
The hemophilia allele is shown with a _________ letter.
Correct Answer: lowercase
Question 8:
A _________ is a chart that shows all the possible combinations of alleles that can result from a genetic cross
Correct Answer: Punnett Square
Question 9:
The combination of alleles is called the _________.
Correct Answer: genotype
Question 10:
The physical appearance is called the _________.
Correct Answer: phenotype
Educational Standards
Teaching Materials
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