Welcome to CCA Genetic Counseling!
Focus Question: how can the knowledge of the inheritance of both sex-linked and autosomal traits be used to predict
the chances that a couple's offspring will have a given genetic disorder?
For this assessment, you and your classmates work collaboratively as a genetics counseling team. Couples come to you
for advice on their risk factors for having a child that has a disorder that runs in their family. For each of the following
scenarios, you will document your problem-solving in your scientist notebook, making sure to:
-draw a family pedigree
-label possible genotypes for each individual
-draw a punnet square for the couple (you may need to draw more than one if the parents have more than one
possible genotype)
- write a rough draft of a report that explains to the couple their odds of having a child that is a carrier or has the
disorder.
While each member will work on the pedigrees, genotypes and punnet squares for each scenario (to reduce errors and
check each other), each team member will serve as the "Lead" genetics counselor on a different scenario and will write
the rough draft of the report for their scenario in their own notebook.
ASSUMPTIONS: if the couple does not mention having the disorder themselves, you assume they do NOT have the
disorder.
Lead counselor:______________________________
Scenario 1: A couple describes their family history of a disorder in the following way (the husband is talking):
"My little sister has cystic fibrosis and my wife's older brother died from complications of cystic fibrosis before she was
born according to her parents. What are the chances we are carriers of this disorder? If we are carriers, what are the
chances that our children will be born with cystic fibrosis?"
Lead counselor:______________________________
Scenario 2: A couple describes their family history of a disorder in the following way (the wife is talking):
” My dad is colorblind and so is my husband. When we have children, what are the odds that they will be colorblind? Or
carriers? Oh, and my sister wanted me to ask you what were her odds of being a carrier for the colorblind gene since we
were meeting with you."
Lead counselor:______________________________
Scenario 3: A couple describes their family history of a disorder in the following way (the husband is talking):
"My father has just diagnosed with Huntington's Chorea and now my wife is talking about starting a family. Can you talk
to us about the odds that I will inherit this disorder? And if I have the disorder, what are the odds that any children we
have will be similarly afflicted??"
Lead counselor:______________________________
Scenario 4: A woman arrives for genetic counseling and this is her concern:
"My husband has just learned that polydactyly** runs in my family. In fact, my brother was born with seven toes on one
of his feet and six fingers on each hand! This is kind of freaking him out. I am pregnant. Might my child have this
condition?"
**(As a genetic counselor, you understand that polydactyly is a dominant disorder in which children are born with extra
toes or fingers. This deformation is easily corrected with surgery.)
Quick review:
Fill in the blanks as a review of the content we have already learned in preparation for today's activity.
Any child that is born receives two copies of a gene for a given trait, one comes from the ______ and one comes from
the __________. These "copies" are called ______________.
For some traits, a simple pattern of inheritance can be seen. One version of the allele is ___________ and will be
expressed in the child if even one copy is present. The other version of the allele is __________ and the child must have
two copies of the allele, one from each parent, in order for that trait to be expressed.
Occasionally, these traits that have a simple pattern of inheritance are found on the _____ chromosome. This increases
the chance of a son having the recessive trait because in this scenario, because the recessive trait can be expressed
when only one copy is present because the dominant trait is not there to "mask" it. These types of traits are called
____________-_____________. In this scenario, if a father has the trait, 100% of his daughters will be __________ of
the trait but would only have the trait themselves if they got a copy of the gene from their ________ as well.
Not all traits have a simple pattern of inheritance. Some are controlled by many genes and are referred to as
____________ traits. Human attributes like height, skin color, and some diseases are controlled by this style of
inheritance and will often show a distribution of traits in a large population that resembles a __________ __________
with only a few individuals with the extreme version of the trait.
Post-writing activity:
If a couple came to you about the chances of their child developing diabetes based on having grandparents with type II
diabetes, what advice could you give them? Why is this scenario different from the ones your team looked at above?
Questions to provide during the activity:
How is this trait inherited?
Is this trait dominant or recessive?
What MUST the genotype of the grandparents be if they had a child with the disorder?
Where must one of the daughter's X chromosomes come from?
Select and sequence: as students work, determine the groups with a good basic understanding of what should be
communicated to the parents--both basic and advanced and then share out results
Finished early? research if a test exists to determine if a person is a carrier and add that to your counseling statement