Framework for Teachable Unit
Topic: Sex-Linked Inheritance
Group Members’ Names: Geeta Kumar, Diana Libuda, Kristin Latham, Rou-Jia Sung, Aaron Payette, and Darcie
McClelland Descalzo
Learning Goals:
1) Understand how genes and chromosomes relate to traits.
2) Appreciate how traits are passed from parents to offspring.
3) Comprehend the inheritance of genetic disorders.
Learning Objectives:
1) Be able to diagram a single-trait sex-linked cross and calculate genotypic/phenotypic ratios.
2) Determine if a genetic disorder is sex-linked by analyzing a pedigree.
3) Distinguish between dominant versus recessive genetic disorders.
Summative Assessments (describe how you would assess your objectives and paste in any summative assessments you have
created):
1) Colorblindness is an X-linked recessive trait. If a father who is XRY has children with an XrXr mother, what is the probability
(percentage) that a daughter born to the couple would be colorblind?
a. 0%
b. 25%
c. 50%
d. 75%
e. 100%
2) Analyze the following pedigree for the pattern of inheritance, and answer the following questions. Assume that individuals II-1 and
II-4 do not have the detrimental allele.
Is this a dominant or recessive trait? Additionally, circle the couple that best supports your reasoning and explain.
Is this a sex-linked trait? Why or why not?
What is the genotype of individual I-1? Explain your reasoning.
Formative Assessments (activities/instruction you designed to teach the learner; please describe your instructional methods
referring your PowerPoint presentation so that others could give this presentation at their own institution.)
1) Students will answer the following clicker question:
Which of the following genotypes is representative of an affected female for hemophilia, an X-linked recessive disorder?
A. AA
B. XaY
C. aa
D. XaXa
E. XAXa
After answering and discussing the previous question, the students will answer the following (second) clicker question:
Which of the following genotypes is representative of a carrier for hemophilia, an X-linked recessive disorder?
A. AA
B. XaY
C. aa
D. XaXa
E. XAXa
Next, we posed the following questions to the class, had them conduct a think-pair-share exercise, and then report out:
Do you think males can be carriers for sex-linked disorders? Why?
2) Students will receive a handout with the following pedigree of a recessive sex-linked disorder:
a a
XX
A
XY
A A
XX
a
XY
They must fill in phenotypes for generation I individuals, and genotypes and phenotypes of all generation II individuals. They will
work in pairs first, and then discuss with the rest of their group. We will then ask for groups to volunteer their results.
a a
XX
A
A A
XY
a
XX
XY
\
A a
XX
a
XY
A a
XX
Next, we will have the students work in pairs to draw in one daughter and one son for generation three. Their pedigree will look like
the one immediately above. They will then cross the two parents to determine the possible genotype/s and possible phenotype/s for
the daughter and son. Working as a group, they will consider the following questions:
If II.2 and II.3 have children, is it possible for them to show the trait? If so, can both boys and/or girls show the trait?
3) Next, the students will conduct an exercise to determine the various genotypes and phenotypes of the boy and girl in generation III.
They will follow these directions:
You have each received a pair of cards representing alleles for the proud parents-to-be from Generation II. Now:
1) Find a partner with the opposite color cards.
2) Hold your cards behind your back, one in each hand.
3) Have your partner randomly select one of your hands.
4) Place your selected card on the table.
5) Repeat 3-4 with your partner’s cards.
6) Now define your offspring’s genotype.
7) ONE OF YOU report your offspring by clicking the
appropriate choice.
The possible responses the student pairs can give using their clicker are as follows:
A. XaXa
B. XAXa
C. XaY
D. XAY