Name
Date
Class
Family Puzzle
Joshua and Bella want to know the probability that any future children they
have might inherit cystic fibrosis like their son Ian. Use the information in
the Case Study to predict this probability.
INQUIRY FOCUS Interpret Data
Procedure
Case Study: Joshua and Bella
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Ian has been diagnosed with cystic fibrosis.
Joshua and Bella are both healthy.
Bella’s parents are both healthy.
Joshua’s parents are both healthy.
Joshua’s sister, Sara, has cystic fibrosis.
Materials
24 allele cards
1. Read the Case Study. In your notebook, draw a pedigree that shows all the family
members. Use circles to represent females, and squares to represent males.
2. Cystic fibrosis is inherited through a recessive allele. To help you figure out the
family pedigree, you will use allele cards. The letter N represents the dominant
allele, while n represents the recessive allele.
3. Use the cards to represent Ian’s alleles. Write his genotype next to his
pedigree symbol.
4. Write Sara’s genotype next to her pedigree symbol.
5. Now use the cards to figure out what genotypes Joshua and Bella must have.
Write their genotypes next to their symbols in the pedigree.
6. Use the cards to figure out the remaining genotypes. Fill in the genotypes next
to the symbols. If more than one genotype is possible, write in both genotypes.
Shade the circles or squares to represent the individuals with cystic fibrosis.
Think It Over
If Bella’s father’s genotype is NN, does that allow you to determine her mother’s
genotype? Explain.
What is the probability that Joshua and Bella will have another child with cystic
fibrosis? What is the probability that they will have a healthy child?
HUMAN GENETIC DISORDERS
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