Date _______
Punnett Square Problems
Genes and Alleles in Mendel’s Pea Plants
Gene
Dominant Allele
Leaf Size
Large (L)
Flower Color
Blue (B)
Plant Height
Tall (T)
Seed Color
Green (G)
1. Make a Punnett Square for Ll x ll
Name __________________
Recessive Allele
Small (l)
Yellow (b)
Short (t)
Yellow (g)
5. Cross a plant that is heterozygous for blue
flowers with a plant that has yellow flowers.
a. Give the genotype ratio.
a. Give the genotype ratio.
b. Give the phenotype ratio.
b. Give the phenotype ratio.
2. Make a Punnett Square for BB x Bb
a. Give the genotype ratio.
b. Give the phenotype ratio.
3. Make a Punnett Square for Tt x Tt
a. Give the genotype ratio.
6. Cross a homozygous tall plant with a short plant.
a. What is the genotype of the offspring?
b. What is the phenotype of the offspring?
7. When a tall plant is crossed with a short plant,
some of the offspring are short.
a. What are the genotypes of the parent
plants?
b. Give the phenotype ratio.
4. Cross two plants that are heterozygous for
green pods.
b. What are the genotypes of the offspring
plants?
c. What is the phenotype ratio of the
offspring plants?
a. Give the genotype ratio.
b. Give the phenotype ratio.
8. What cross would result in ½ of the offspring
having green seeds and ½ of the offspring
having yellow seeds
Date _______
Punnett Square Problems
Name __________________
1. Cystic Fibrosis is a genetic disease caused by a recessive allele. Those who have cystic fibrosis
usually die at a young age because their body constantly produces mucus that clogs their airways
and they suffocate. Two healthy adults have a child who suffers from cystic fibrosis.
a. What is the genotype for the parents?
b. Draw the Punnett Square for the parents.
c. What are the chances that their second child will
have cystic fibrosis?
2. Achondroplasia is the most common form of dwarfism and it is passed from one generation to the
next as a dominant allele. Two heterozygous dwarf parents are expecting a baby. They want to
know the chances that their child will be normal height so they can figure out if they should start
buying normal sized chairs.
a. Draw the Punnett square for the parents.
b. What are the chances that they will have a normal
sized child?
3. Albinism is a condition where your body does not produce pigments. A John, who has albinism,
marries Maria, who has normal skin pigment. John believes that if he and Maria were to have a
child, the child would not be albino because neither of his parents where albino. However, albinism
runs in Maria’s family. Maria’s mother was an albino.
a. What are the genotypes for John’s parents
b. Draw a Punnett square for John’s parents and give the
genotype ratio.
c. What is the genotype for Maria’s mother?
d. Can you determine the genotype of Maria’s father? Explain
why or why not.
e. Draw a Punnett square for John and Maria and give the
phenotype ratio.
Date _______
Punnett Square Problems
Name __________________
4. Some guy from the Maury Show(Billy) is accusing his girlfriend(Bobby Jo) of cheating because they
both have blue eyes, yet their kid has brown eyes. Assume that brown eyes are dominant to blue
eyes.
a. Draw a Punnett square for Billy and Bobby Jo. Give
the genotype ratio.
b. Will the DNA test reveal that Billy is the father of Bobby
Jo’s child? Explain.
5. Eric can play songs on the piano that very few other people can play because he has six fingers on
each hand. This condition is known as polydactylism and it is passed on as a recessive trait. Eric was
hoping that he could pass on this trait to his children so they can also be musical prodigies.
He marries Alice and they have 7 children and all of which have the normal number of fingers.
a. What is the likely genotype of Alice.
b. Draw a Punnett square for Alice and Eric.
c. What are the chances that Alice will give Eric a child
with six fingers.
He then marries Samantha and they have 4 children, 2 have polydactylism and the other 2 have the
normal number of fingers.
d. What is the likely genotype of Samantha.
e. Draw a Punnett square for Samantha and Eric and
give the genotype ratio.
6. Annie is an orphan with red hair and freckles. Neither one of her parents had freckles. Her mother
had red hair and her father had brown hair. Looking at a photograph of her grandparents on her
father’s side, she could see that they both had red hair.
a. Which allele is dominant, freckles or no freckles?
Explain or show Punnett square.
b. Which allele is dominant, brown hair or red hair?
Explain or show Punnett square
.