Pedigree Key 1
Unaffected Male
(Healthy –Normal)
Page 1 of 3 From Punnett Squares to Family Trees and Pedigrees
SJB Revised 3/22/2016
Name: ___________________________ Per. _____
Unaffected Female
(Healthy – Normal)
Cystic Fibrosis (CF) is an exocrine system disease condition
that is characterized by difficulty in breathing (lung function)
and digestive system issues.
Male w/ Phenotype
(Disease Condition)
Cystic Fibrosis (CF) is caused by a defective autosome gene
which causes the body to produce abnormally thick and sticky
mucus. This mucus builds up in the breathing passages of the
lungs and in the pancreas, the organ that helps breakdown and
absorb food. This collection of sticky mucus results in lifethreatening lung infections and serious digestive problems.
The disease may also affect the sweat glands and a man’s
reproductive system.
Female w/ Phenotype
(Disease Condition)
Male Carrier
(Healthy)
Female Carrier
(Healthy)
Millions of Americans carry the defective CF gene, but do not
Deceased Male
have any symptoms. That’s because a person with CF must
inherit two recessive defective CF genes---one from each
parent. An estimated 1 in 29 Caucasian Americans have the
Deceased Female
CF gene. The disease is the most common, deadly, inherited
disorder affecting Caucasians in the United States. It’s more
common among those of Northern or Central European descent. Most children with CF are
diagnosed by age 2 years. A small number, however, are not diagnosed until age 18 years or
older. These patients usually have a milder form of the disease. 1
The Pedigree Diagram 1 below traces two generations of a family affected by (CF). Refer to the
Pedigree Diagram 1 and Pedigree Key 1 to answer the associated questions on the following
pages.
1
7
3
2
4
8
5
9
6
The first generation husband and wife, individuals #s 1 & 2, do not have Cystic Fibrosis and did
not realize they were carriers until the birth of their fourth child (individual #6). Their daughter
died from (CF) complications when she was 7 years old. Now their other three children are all
grown and married. They are considering having children and all are concerned about the
possibility of having a child with (CF).
1
Information from: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001167/
Page 2 of 3 From Punnett Squares to Family Trees and Pedigrees
SJB Revised 3/22/2016
Name: ________________________________________ Per. _____ Date: _________________
Cystic Fibrosis Pedigree Questions
Refer to Pedigree Diagram 1 and use your knowledge of genetics and your ability to create
Punnett squares to answer the following questions. Where indicated, complete an associated
Punnett square.
For the Punnett square designate the trait of Cystic Fibrosis with the letters “C” and “c”
1. _____ Based on the Pedigree Chart, the allele for Cystic Fibrosis is
A. X linked Dominant
B. X linked recessive
C. Autosomal Dominant
D. Autosomal recessive
2. Using your pedigree analysis and answer to question # 1, complete the following:
A. The Dominant allele is Normal or Cystic Fibrosis (circle one)
B. The normal allele is represented by
a) A Capital “C”
b) A lowercase “c”
C. The Cystic Fibrosis allele is represented by
a) A Capital “C”
b) A lowercase “c”
3. How many of the first generation couple’s (individuals # 1 & 2) children (individuals #s 3, 4,
5, & 6) are:
A. Unaffected healthy normal individuals? _________
B. Healthy carriers? _____________
C. Have the phenotype disease condition? ___________
4. Create a Punnett square based on the parents’ (#1 & #2) genotypes to answer the following:
What was the probability of having a child with the Cystic Fibrosis phenotype?
♂
A. 100%
♀
B. 75%
C. 50%
D. 25%
1
Information from: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001167/
Page 3 of 3 From Punnett Squares to Family Trees and Pedigrees
SJB Revised 3/22/2016
Create a monohybrid Punnett square probability cross for Cystic Fibrosis for each of the
surviving children and their spouses to predict the chances of having a child with Cystic Fibrosis.
Use the Punnett squares to answer the following questions (must show your work).
5. _____ What is the probability of couple A having a child with
Cystic Fibrosis?
A. 0%
B. 25%
C. 50%
D. 75%
E. 100%
6. _____ What is the probability of couple B having a child with
Cystic Fibrosis?
A. 0%
B. 25%
C. 50%
D. 75%
E. 100%
7.
1
Couple A: Individuals #s 3 & 7
Couple B: Individuals #s 4 & 8
_____ What is the probability of Couple C having a child with Couple C: Individuals #s 5 & 9
Cystic Fibrosis?
A. 0%
B. 25%
C. 50%
D. 75%
E. 100%
Information from: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001167/