Practicing Punnett Squares and Pedigrees
Directions: Answer the following questions on a piece of binder paper. Be sure to show Punnett
squares and pedigrees (including genotypes) to prove your answers.
Case Study: Sickle Cell Anemia
Sickle­cell anemia is known to be a hereditary disease. It has a pattern of inheritance that closely
follows the model for recessive traits described by early geneticist Gregor Mendel. For a recessive
trait to appear, a person must have inherited two copies of the recessive gene.
1. John and his wife Anna are heterozygous for Sickle­cell. Create a Punnett Square to analyze the
odds of any offspring inheriting sickle­cell anemia.
2. If their child who has both normal hemoglobin genes marries a person who has sickle­cell
anemia, what is the probability of any of their offspring inheriting sickle­cell anemia (use a
Punnett square)?
3. If a person has anemia, his or her blood cells are oxygen deprived. Describe to this couple how
a person with sickle­cell anemia might feel.
4. Why would simple blood transfusions not be able to cure this disease?
5. Make a Pedigree of John and Anna’s family. They have one non sickle­cell son who married a
normal female. However the son has an infected daughter. Show all genotypes.
Punnett Squares and Pedigrees: Why Do I (or don’t I) Have Freckles and Curly Hair?
Solve the genetics problems below by using Punnett squares and pedigrees. Write your answers on a
separate piece of paper.
The gene for freckles has two alleles.
F =freckles (dominant allele)
f=no freckles (recessive allele)
1. a. Dan is heterozygous for freckles. His wife, Deborah, does not have any freckle. Create a
Punnett square to predict the results of their children.
b. What percentage of their children will have freckles?
c. What percentage of their children will not have freckles?
d. Make a pedigree of Dan’s family if he had 3 sons; the oldest has freckles, the others do not.
2. a. Sara and Justin both have freckles and both are heterozygous for this trait. Create a Punnett
square to predict the results of their children.
b. What are the chances they will have a child with freckles?
c. What is the chance they will have a child with the FF genetic makeup?
d. Make a pedigree for Sara, Justin, and both their parents. Justin’s mom and Sara’s dad both
have freckles.
3. a. Make a pedigree for YOUR family’s freckles genes. Include your parents and siblings.
b. Include all genotypes.
The gene for hairstyle has two alleles.
H= curly hair (dominant allele)
h= straight hair (recessive allele)
4. Gloria has straight hair and her husband, Andre, also has straight hair. Make a pedigree of their
family, which includes 2 girls and a boy. The boy is the youngest. Don’t forget genotypes.
5. Make a pedigree for Maria’s family; Maria has straight hair. Her mother, Irma, has curly hair and
her father, Pedro, also has curly hair. Maria has an older sister with curly hair, but who has a
straight haired son. Maria also has a younger brother with straight hair, whose daughter has curly
hair. Maria has 2 children, a son with curly hair, and a daughter with straight.
6. a. Do you have curly hair or straight hair? What is your genotype?
b. Make a pedigree of your immediate family (parents and siblings) to determine your genotype.
Include all family members’ genotype.