Download cystic fibrosis pedigree

CYSTIC FIBROSIS PEDIGREE
Cystic fibrosis is a genetic disorder. Individuals with CF have an excess amount of fluid produced in
their lungs, leading to severe respiratory problems. People with CF often die within their first year of
life.
The gene for CF is not found on the sex chromosomes. Therefore, males and females will each have
two CF alleles in their genotype. The dominant allele for cystic fibrosis gene is “F”, for normal fluid.
The recessive allele is “f” for too much fluid. Heterozygotes, “Ff”, have the normal amount of fluid in
their lungs. Heterozygotes are also called carriers of the CF gene because even though they do not
have the disease, they can pass the recessive allele to their offspring.
STEP 1:
Complete the key to the right of the pedigree by coloring in appropriate circles and
boxes and by writing the appropriate genotypes (FF, Ff or ff).
STEP 2:
Use the pedigree to answer the analysis questions.
KEY
1
2
normal female, ____
affected female, ____
3
4
5
6
normal male, ____
affected male, ____
7
8
1. How many generations are represented in the pedigree? _________
2. How many offspring did the first couple have? __________
3. How many males have CF? _______ How many females have CF? _______
4. What is the genotype of individual 4? _______
5. Which individuals must be carriers of the recessive CF allele? ____________
6. A woman and man are both heterozygous for the CF gene. They want to have a child
but are worried that their baby will inherit CF. What is the likelihood that their baby
will be affected by CF? Use a Punnett Square to support your conclusions.
DIRECTIONS: For each pedigree, use the key and alleles to determine the genotypes of the unnumbered
individuals. Write individual genotypes on the lines provided.
PEDIGREE 1: Dominant Trait: Huntington’s Disease (H,h)
KEY
2
1
normal female
affected female
5
4
3
normal male
affected male
6
Genotypes:
1. ______
2. ______
3. ______
4. ______
5. ______
6. ______
PEDIGREE 2: Codominant Trait: Blood Type (A, B, O)
AB
Genotypes:
A
1
B
A
B
2
3
B
4
O
A
9
B
O
5
6
A
B
A
7
8
AB
O
O
1. ________
7. ________
2. ________
8. ________
3. ________
9. ________
4. ________
10. ________
5. ________
11. ________
6. ________
12. ________
AB
A
B
10
11
O
B
12