Download Lesson Plans

67
40
1
50 -m
i n ut e s
e ss
io
VE
R
-
to
ns
What Would You Do?
O
ACTIVIT Y OVERVIEW
T
TA L KI N G I
SUMMARY
Students return to Joe’s dilemma and consider whether he should be tested for the
Marfan syndrome. This activity provides more information about the Marfan syndrome and also allows students to consider further how a diagnosis of a genetic condition might affect a person. They consider the trade-offs involved in finding out if
you have a disease as they write Joe a letter telling him whether they think he should
submit himself to genetic testing.
KEY CONCEPTS AND PROCESS SKILLS
1.
Some medical conditions and diseases are genetic.
2.
Understanding the principles of genetics can help individuals to make
decisions about genetic conditions and genetic testing.
3.
In some cases, the presence of a genetic condition can be established by
genetic testing.
4.
The Marfan syndrome is an inherited disease that affects a person’s connective
tissue and is characterized by a pattern of symptoms, some or all of which may
be displayed by an individual with the syndrome.
5.
A person with the Marfan syndrome can live a full productive life, but may
have to avoid some physical activities and monitor his/her health.
6.
Pediatric genetics and genetic counseling are careers that require a background
in genetics.
7.
There are personal and social trade-offs associated with knowing one has a
genetic condition.
KEY VOCABULARY
DNA
mutation
dominant
probability
homozygous/heterozygous
trait
Teacher’s Guide
D-171
Activity 67 • What Would You Do?
MATERIALS AND ADVANCE PREPARATION
For the teacher
1
Transparency 67.1, “Pros and Cons of Genetic Testing”
You may want to have students review Activity 56, “Joe’s Dilemma,” for homework
the night before doing this activity.
TEACHING SUMMARY
Getting Started
1.
Review Joe’s story.
Doing the Activity
2.
Students read the email from Joe to Megan and develop a list of pros and cons
of genetic testing.
3.
The class discusses the science and societal issues related to Joe’s situation.
Follow-Up
4.
Students respond to the Analysis Questions and discuss their
recommendations to Joe.
Extension
Students use the SALI page of the SEPUP website as a starting point for research on
genetic conditions and issues related to genetic conditions and genetic testing.
BACKGROUND INFORMATION
The Marfan Syndrome
The Marfan syndrome is caused by a defect in a critical connective tissue protein (fibrillin). Because of this, many parts of the body can be affected. Most important among
these are the skeletal system (spine curvature, chest deformation), the eyes (lens dislocation, retinal detachment), and especially the cardiovascular system (heart valve
defects, aortal swelling and tearing).
The aorta is the culprit in most cases of sudden, unexpected deaths from the Marfan
syndrome and related disorders. Thus, the health of the aorta is one important reason
why physicians want to diagnose the Marfan syndrome early, during childhood if
D-172
Science and Life Issues
What Would You Do? • Activity 67
possible. Managing the condition, through limiting strenuous activity, is the frontline
strategy; however, aortic surgery is frequently performed, either as a preventive measure or in response to severe aortic swelling. An artificial valve and a variable amount
of prosthetic aorta are used to replace the weakened tissue, thereby significantly
improving the individual’s chance for a full lifespan.
The Marfan syndrome can be caused by a dominant mutation in any one of several
connective tissue genes, but for purposes of pedigree analysis and genetic counseling
it can be considered a one-gene trait.
Huntington’s disease
Another dominant condition that may interest the class is Huntington’s disease. However, the long-term prospects for people with Huntington’s disease are far less optimistic than for people with the Marfan syndrome. The symptoms usually appear in
midlife, although the time of onset is highly variable. Dr. Nancy Wexler’s father
founded the Hereditary Disease Foundation after her mother was diagnosed with
Huntington’s disease. Dr. Wexler, originally trained as a clinical psychologist, has used
the classical approach of tracing Huntington’s disease through family pedigrees as
well as modern laboratory techniques to find the gene for this disease. She has built
on the work of earlier scientists and collaborated with other scientists from all over
the world. She is now a professor at Columbia University, president of the Hereditary
Disease Foundation, and chair of the Ethics Working Group within the Human
Genome Project.
REFERENCES
http://www.marfan.org. The National Marfan Foundation. The website, together
with mailings sent upon request, offers useful resources for any age level.
Pyeritz, Reed E. and Cheryl Gasner. The Marfan Syndrome. New York: National
Marfan Foundation, 1994.
Teacher’s Guide
D-173
What Would You Do? • Activity 67
analyze the trade-offs of a decision. Ask students to
TEACHING SUGGESTIONS
work in groups for about 5 minutes to come up with
some pros and cons to add to the transparency.
GETTING STARTED
1.
They should record their ideas. Then have each
group suggest one pro or con to add to the chart on
Review Joe’s story.
Tell students that they now have a chance to
reconsider Joe’s dilemma and make a recommendation to him about whether to be tested. Have
them re-read Activity 56, “Joe’s Dilemma,” silently or to one another in groups of four students, if
you did not assign it as homework. Also have them
review their answers to the Analysis Questions
from Activity 56, or use the questions to spark a
short review discussion.
the transparency. Some of the ideas they are likely
to come up with follow in the table below.
3.
The class discusses the science and societal
issues related to Joe’s situation.
Discuss the genetic basis of the Marfan syndrome as
a trait determined by a single mutant allele (a dominant trait). Respond to any questions students may
still have about the genetic basis of the syndrome.
Students may be curious about the use of heart
surgery. If so, use the Background Information sec-
DOING THE ACTIVIT Y
2.
Students read the email from Joe to Megan
and develop a list of pros and cons of
tion as a resource for additional information. Students may also wish to further research this question on the Internet.
genetic testing.
Select students to read each of the paragraphs of the
email aloud. Then display Transparency 67.1, “Pros
and Cons of Genetic Testing.” Tell students that
making a chart of pros and cons can help them to
Explain that genetic counselors work with people
who may have genetic conditions. They help people
decide whether to be tested, and help people diagnosed with genetic conditions understand how likely it is that their children will inherit the condition.
Pros
Cons
Would know one way or other, and wouldn’t
be uncertain any more.
Father is against testing.
If test is negative, can forget the whole thing
for good.
If the test is positive, would worry about the condition.
If test is positive, could be careful about
exercise and reduce risk.
Have to give up soccer and scholarship.
If the test is positive, could get check-ups and
if needed have surgery to prevent serious
heart problems.
Insurance company might deny health insurance.
If the test is positive, Joe would know if his
children would be likely to be affected.
Others, such as employers, might discriminate.
Teacher’s Guide
D-175
You may wish to show again some of the parts of
idea that the probability of a “spontaneous” occur-
the video used in Activity 56 to highlight the role of
rence of a genetic condition is very low. However, it
the genetic counselor working with people. At this
does occasionally occur. In fact, a significant per-
time, students will be able to understand some of
centage of individuals with the Marfan syndrome
the comments the genetic counselor is making
appear to have a new mutation that arose random-
when she uses a pedigree to discuss the probability
ly during development of the egg or sperm.
of a child inheriting the Marfan syndrome. Ask students for their reactions to the issues of discrimination by employers and insurance companies that
are raised by Joe’s situation. Ask, Do you think we
need more laws to prevent discrimination against
people with genetic conditions? Who should pay
for the tests and treatments? As more and more
information about our genes becomes available,
how will individuals and society respond to all of
the information?
Analysis Questions 2 and 3 provide assessment
opportunities and should be answered individually.
Question 2 is similar to Analysis Question 5 in Activity 59, “Gene Combo,” and can be used to assess
whether students understand the concept of dominance and realize that a dominant trait need not be
more common in the population (it is simply the
trait that appears in a heterozygous individual). Their
responses can be scored with the U NDERSTANDING
C ONCEPTS (UC) scoring guide. Analysis Question 3
Students may ask if there are cases of insurance
can be used to assess either aspect of the C OMMUNI -
being denied to individuals with genetic disorders.
C AT I N G
There are in fact a number of such cases, and there
well as the “Using Evidence to Make Trade-offs” ele-
is growing concern about where this will lead as the
ment of the E V I D E N C E
genetic basis of more conditions is established sci-
able. The response should be written as an email to
entifically, and as it becomes possible to diagnose
Joe from his friend’s perspective. This letter should
more such conditions based on genetic testing.
describe the pros and cons, but should also include
S C I E N T I F I C I N F O R M AT I O N (CM) variable as
AND
T R A D E - O F F S (ET) vari-
the friend’s final recommendation and how he/she
FOLLOW–UP
4.
Students respond to the Analysis Questions
and discuss their recommendations to Joe.
Analysis Question 1 can be assigned for individual
response or can be the basis of a class discussion.
After you review Question 1, you may wish to ask,
If Joe does not have the Marfan syndrome and
decides he wants to have a child someday, what
are the chances the child will have the Marfan syndrome? (Assume that the child’s mother does not
have the Marfan syndrome either.) This question
provides you with an opportunity to discuss the
D-176
Science and Life Issues
weighed the pros and cons of the testing. If you are
using the question as an assessment, review the scoring guides that you will use to assess the letter.
Review students’ responses. You may wish to have a
few students share their responses with the whole
class or have each group of four students read their
answers to one another.
Extension
Students use the SALI page of the SEPUP website
as a starting point for research on genetic conditions and issues related to genetic conditions and
genetic testing.
What Would You Do? • Activity 67
For links to more information on genetic
the child’s mother does not have the Marfan
conditions, have students go to the
syndrome.) Make a Punnett square and explain
SALI page of the SEPUP website.
your answer.
Students may also check current
M
m
m
Mm
mm
m
Mm
mm
news reports and research laws against genetic
discrimination at the state and national levels.
SUGGESTED ANSWERS
TO ANALYSIS QUESTIONS
1.
Joe’s family pedigree is shown below. How would a
Joe’s alleles are shown at the top. This assumes
genetic counselor answer the following questions?
he is heterozygous, as discussed in Analysis
Question 1a. Joe’s future partner’s (the moth-
?
er’s) alleles are shown at the left. Since she does
not have the syndrome, she is homozygous
recessive. The square shows that the child has a
?
?
50% chance of having the Marfan syndrome
because he or she has a 50% chance of receiving
a Marfan allele from Joe.
?
Joe
?
2.
The Marfan syndrome is a dominant UC
trait. Write your own definition of dominant
trait as it is used in genetics. Use evidence to explain
a.
If Joe has the Marfan syndrome, is he likely to
be homozygous or heterozygous? Explain your
whether the dominant trait is always the most common trait in a human population.
answer.
A sample level 3 response follows.
If Joe has the Marfan syndrome, he is likely to
be heterozygous. There is no evidence that his
Dominance has nothing to do with how com-
father has the Marfan syndrome; since the syn-
mon a trait is. The dominant trait is whatever
drome is dominant, the father does not have an
trait you see when an individual is heterozy-
allele for the condition. (Therefore Joe is het-
gous for a gene. The trait that is dominant
erozygous; he received a normal allele from his
might be common (such as the case of PTC tast-
father as well as a Marfan-causing allele from his
ing) or very rare in the population (such as poly-
mother.)
dactyly or the Marfan syndrome).
b.
If Joe has the Marfan syndrome and has a child
someday, what is the probability that his child
will have the Marfan syndrome? (Assume that
A level 4 response might highlight the idea that
if the allele for a dominant trait is very rare in
the population, that condition will be rare.
Teacher’s Guide
D-177
Activity 67 • What Would You Do?
3.
Pretend that you are Joe’s friend. Write
a letter to Joe telling him whether you think
he should be tested.
ET
uet
terrible and is the one big risk of testing, as far
CM
won’t let that happen to you.
as I can see. It sounds like the laws in our state
Hint: To write a complete answer, first state your
Even if you have to take the risk with your
opinion. Provide two or more pieces of evidence that
health insurance, the decision seems clear to
support your opinion. Then consider all sides of the
me. I don’t want anything to happen to you,
issue and identify the trade-offs of your decision.
Joe; please have the test.
Student answers will vary. Level 3 answers for
Hey Joe—
and against testing follow. Be sure that students
I don’t think you should have the test. You’re
realize the serious risk involved in not being
probably so tall because you’re from a tall fam-
tested and the importance of taking appropri-
ily. What if your mom didn’t actually die from
ate precautions if the test is positive.
the Marfan syndrome? Your uncle and grandfa-
Hi Joe—
ther are healthy, so you might be healthy too—
I doubt any of you have the Marfan syndrome.
I’ve thought a lot about your email. I think you
should get the test. If you don’t get the test, you
will just worry anyway, so you might as well
know one way or the other if you have this
thing. If you don’t have it, you can stop worrying and enjoy soccer. If you do have it, I know
You love soccer, and your dad was counting on
you getting that scholarship. The scholarship
will help you get a good education, and that’s
important. You don’t want to risk being discriminated against when you need health insurance or a job.
giving up soccer would be hard for you, and
that’s a tough trade-off, but think of the advan-
I guess the biggest trade-off is that you are taking
tages of knowing. You can take care of yourself,
a risk with your health. But it doesn’t seem that
get your heart checked out, and if worse comes
big a risk, since you’re healthy so far. Look at
to worse, have the surgery to fix your aorta.
Abraham Lincoln—people think he had the Marfan syndrome, but it didn’t stop him! Take care of
You should try to talk your dad into going along
with you. After all, it’s your life! The health
insurance question is tricky, but maybe you can
find out more. Losing your insurance would be
D-178
Science and Life Issues
yourself. Get a lot of checkups to be sure your
heart is okay. Maybe you can get the test in a few
years. Right now, it’s more important to move on
with your plans and not worry so much.
Pros and Cons of Genetic Testing
Cons
©2006 The Regents of the University of California
Pros
Science and Life Issues Transparency 67.1
D-179