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Name________________________ Period_____ Date______ Lab #______ Regents Biology
Genetic Disorders: Case Studies
Genetic disorders are diseases that are caused by an abnormality or mutation in an individual’s
DNA. Mutations in the DNA can range from a small, single base change to the addition or deletion of
an entire chromosome. You can be born with these DNA mutations as a result of your mother or
father, or both, passing on their mutations to you, if they are in your dad’s sperm and your mom’s
egg. Mutations in your DNA can also arise later in life, possibly from environmental factors such as
excessive alcohol consumption, smoking cigarettes or exposure to UV radiation from the sun.

Define genetic disorders.

How can a child be born with a genetic disorder?

Other than being born with a DNA mutation, list three other factors in your environment that can cause mutations
in your DNA.
There are many types of mutations that can cause genetic disorders. A point mutation is when one
nitrogenous base in the DNA is changed.
Example of a Point Mutation:
Original DNA:
Mutated DNA:

ATTACTATCGAGATTAT
ATTACTATGGAGATTAT
Use a highlighter to highlight or underline where the point mutation has occurred in the mutated DNA strand.
Mutations can also occur when either a nitrogenous base is either added or deleted. The addition of
an extra letter in a gene is called an addition. Deleting a nitrogenous base is called a deletion.
Examples of Addition and Deletion Mutations:
Original DNA:
Mutated DNA #1:
Mutated DNA #2:

ATTACTATCGAGATTAT
ATACTATCGAGATTAT
ATTACTATCCGAGATTAT
Which mutated DNA strand is an example of an addition mutation? __________ How do you know? Be as
specific as possible.
Mutations can be good, bad or have little effect on an organism. Changes in the DNA code do not
always guarantee a change in the amino acid sequence or protein that is made. If the mutation does
not change the sequence of amino acids then it will not change the type of protein being made and
therefore, will have little to no effect on the organism. Some mutations can cause diseases such as
Cystic Fibrosis, Breast Cancer, Sickle Cell Anemia, Downs Syndrome, or Tay Sach’s Disease. These
diseases are examples of when the mutated DNA does cause a change in the amino acid sequence
and therefore, a change in the protein being made.
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Examples of Mutations
Original DNA:
Original RNA:
Amino Acids:
TAC
AUG
Start
Mutated DNA #1:
TAC
Mutated RNA #1:
____
Mutated Amino Acids _____
GGG
CCC
Pro
CGC
GCG
Ala
TTT
AAA
Lys
ATT
UAA
Stop
GGC CGC TTC ATT
_____ ____ ____ _____
_____ _____ ____ _____
In this example, did the amino acid sequence change? If so, describe what amino acid(s) changed.
Did this mutation cause a change in the protein that was made by the DNA? Explain why or why not.
Was this mutation harmful, beneficial or create no change in the person? Explain how you know.
Original DNA:
Original RNA:
Amino Acids:
TAC
AUG
Start
Mutated DNA #2:
TAC
Mutated RNA #1:
____
Mutated Amino Acids _____
GGG
CCC
Pro
CGC
GCG
Ala
TTT
AAA
Lys
ATT
UAC
Stop
GGC AGC TTC ATT
_____ ____ ____ _____
_____ _____ ____ _____
In this example, did the amino acid sequence change? If so, describe what amino acid(s) changed.
Did this mutation cause a change in the protein that was made by the DNA? Explain why or why not.
Was this mutation harmful, beneficial or create no change in the person? Explain how you know.
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Case Study #1: Sickle Cell Anemia
Directions. While watching the short video: “ Sickle Cell Anemia: A Patient’s Journey,” answer the
following questions.
1. What disease does Alexandria have?
2. What cells are deformed in Alexandria’s body?
3. What happens to Sickle Cell patients’ red blood cells when they are flowing through her blood
vessels?
4. What are some symptoms of the disease?
5. Why is Alexandria at risk for organ failure?
6. There is no cure for sickle cell anemia. What do doctors do to help keep patients as healthy as
possible?
7. What is the purpose of the procedure that is used to keep patients healthy?
8. In your group, get a microscope and two blood smears: a prepared sample of Infinity’s blood
and a blood smear of a normal individual. In the area below, sketch the appearance of
Infinity’s red blood cells and a healthy patient’s red blood cells.
Sickle Cell Patient’s Blood Smear
Healthy Patient’s Blood Smear
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10. Make an inference, how do you think the shape of the red blood cells in a sickle-cell patient
may affect how well the cells are able to circulate throughout the blood vessels?
11. What body system is disrupted in Sickle-Cell Anemia patients?________________________
12. Below is a table, comparing the gene mutation that occurred in Infinity’s DNA for making
hemoglobin and the gene for a healthy individual. Complete the mRNA, the amino acid and
shape of red blood cell rows.
DNA Code
Normal Hemoglobin
Sickle Hemoglobin
GGG CTA CTT TTT
GGG CAA CTT TTT
mRNA Code
Amino Acid Order
Shape of Red Blood
Cells
Sickle Cell Anemia is a genetic disease caused by one single base mutation in the DNA. This
disease is recessive, meaning that carriers of the disease do not have symptoms. Therefore, a
seemingly normal couple may have a child with sickle cell anemia. Complete the punnett squares
below to determine the odds of having a child with sickle cell anemia.
Sickle Cell Trait = s Normal Trait = S
13. Complete the punnett square to determine the likelihood of two parents, each heterozygous
for the disease, having a child with sickle cell anemia.
____ % of offspring would have sickle-cell anemia
____% of offspring would not have sickle cell anemia, but would be carriers for the
disease.
____% of offspring would not have sickle cell anemia and would not be carriers for
the disease.
14. Complete the punnett square to determine the likelihood of two parents, one who is a carrier
of the sickle cell trait and one who is homozygous dominant (normal), having a child with sickle
cell anemia.
____ % of offspring would have sickle-cell anemia
____% of offspring would not have sickle cell anemia, but would be carriers for the
disease.
____% of offspring would not have sickle cell anemia and would not be carriers for
the disease.
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Case Study #2: Tay Sach’s Disease
Watch the following video about Hayden, a young boy with Tay Sach’s Disease.
http://www.pbs.org/wgbh/nova/genome/program.html Click on the “One Wrong Letter” link.
1. What were some of the early warning signs that Hayden’s parents noticed by the time he was
a year old, indicating there was something wrong with him?
a. ______________________________________________________________________
b. ______________________________________________________________________
c. ______________________________________________________________________
2. What major organ is affected by children with Tay Sach’s disease?_____________________
3. What major body system is affected? _______________________
4. How many mistakes in the DNA code are there for children with Tay Sach’s disease?______
5. Gene’s (segments of DNA) create_________________.
6. Tay Sach’s patients are missing an important protein in their body that is created by a specific
sequence of DNA. What is the job of this protein normally?__________________________
___________________________________________________________________________
7. How does all of this extra fat building up in the brain affect the child’s brain cells?
___________________________________________________________________________
8. Is there a cure for Tay Sach’s disease?___________ What is the life expectancy of children
with Tay Sach’s disease?______________________________________________________
9. Both parents of Hayden were carriers of the tay-sach’s disease. What does this mean? Did
they have the disease? How did Hayden end up with the disease?
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
10. What ended up happening to Hayden?___________________________________________
11. Complete the following Punnett square to determine if both parents were carriers of the
TaySach’s disease trait, what is the likelihood that they will have a child who actually has the
disease.
Mom
T= Normal Gene (segment of DNA)
t= Tay Sach’s Gene (segment of DNA)
a. What is the probability that they will have a child with
Tay Sach’s Disease? ______________
Dad
b.What is the probability that they will have a child who is a carrier
for the Tay Sach’s trait?____________
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Sickle Cell Anemia
BOTH
Tay- Sach’s Disease
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HUNTINGTON DISEASE FAMILY SECRETS UNIVERISTY OF ROCHESTER
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