Name: ______________________
Date: __________ Period: ______
Punnett Squares
Directions: Read each problem carefully. Make a “key” for the trait (what does each
letter mean), identify the genotypes. Show the Punnett square and give the ratio of both
genotype and phenotype.
Before you begin….Define the following terms from your notes…
 Homozygous
 Heterozygous
 Phenotype
 Genotype
 Dominant
 Recessive
1. In rabbits, black fur is dominant over white fur. Show the cross of a heterozygous black
male with a homozygous white female.
Key:
Genotypes:
2. Tall is dominant over short in pea plants. Show the cross of a homozygous short plant is
crossed with a homozygous tall plant.
Key:
Genotypes:
3. In humans, free-ear lobes are dominant to attached. Two parented that are both
heterozygous free are expecting a child. What are the chances that the child will have
free ear lobes of attached?
Key:
Genotypes:
4. Wrinkled seed are recessive to smooth seeds. Show a plant that always produces
wrinkled seeds crossed with a heterozygous smooth seeds producing plant.
Key:
Genotypes:
5. As in the previous problem… Show a heterozygous smooth plant crossed with another
heterozygous smooth seed producing plant.
Key:
Genotypes:
6. Blue eyes are dominant to red eyes in rabbits. Show a heterozygous blue-eyed rabbit
crossed with a red-eyed rabbit.
Key:
Genotypes:
7. In fruit flies, red eyes are dominant over white eyes. Show a cross between two whiteeye fruit flies.
Key:
Genotypes:
Directions: Complete the following Punnett Squares. Be sure that you include the ratios
of the genotypes (and the words used to describe those alleles) and phenotypes of the
characteristics.
1. B= Brown eyes b= blue eyes
Mom= Bb Dad= BB
What are the eye color possibilities if they chose to have children?
Genotypes
Phenotypes
2. Curly hair is recessive, and straight hair is dominant. A woman with curly hair marries
a man who is homozygous dominant for straight hair. Predict the outcomes for their
children.
Genotypes
Phenotypes
3. Black hair is homozygous dominant. Brown hair is heterozygous. Blonde hair is
homozygous recessive. (This is an example of incomplete dominance.) A woman with
brown hair marries a man with brown hair. What are the possible outcomes for their
kids?
Genotypes
Phenotypes
4. Attached earlobes are dominant over free hanging earlobes. Complete the Punnett
Square for the following individuals: Mom=BB and Dad=bb
Genotypes
Phenotypes
5. Incomplete dominance problem: T=tall (5’11”-6’2”); Tt=medium height (5’4”-5’10”)
t=short (5’3” or smaller)
Mom= 5’5”
Dad= 6’0”
What are the possible height outcomes of their children?
Genotypes
Phenotypes
6. Freckles are recessive. No freckles are dominant.
Mom= heterozygous Dad=homozygous recessive Possible outcomes for kids?
Genotypes
Phenotypes
Type of Inheritance: Dominant/Recessive
1. Apples can have a long stem or a short stem. Long stem (L) is dominant. Use a Punnett
Square for a cross between
a Long stem apple (LL) and
GENOTYPES
PHENOTYPES
a short stem apple (ll).
Show all percentages or
ratios of genotypes and
phenotypes.
2. In humans, hitchhikers
thumb (H) is dominant to
straight (h) thumbs. Use a
Punnett Square to show the
possible offspring for a
cross between a
heterozygous parent (Hh)
and a straight thumb
parent (hh). Show all
percentages or ratios of
genotypes and phenotypes.
GENOTYPES
PHENOTYPES
3. The type of running gait of horses is inherited. Trotting is due to a dominant gene (T) and
pacing is a recessive allele (t). If two hybrid trotters (Tt) are crossed, what are the possible
outcomes? Use a Punnett
Square to show all ratios of
GENOTYPES
PHENOTYPES
genotypes and phenotypes.
THE FOLLOWING PROBLEMS
HAVE CERTAIN THINGS
MISSING FROM THE QUESTION
THAT YOU HAVE TO FIGURE
OUT. BE CAREFUL THAT YOU ARE SETTING UP THE CROSS CAREFULLY. MAKE NOTES IN THE
MARGINS IF YOU HAVE TO.
4. Tomatoes can be red (R) or
yellow (r). If a homozygous
dominant tomato plant is
crossed with a homozygous
recessive tomato plant, what
GENOTYPES
PHENOTYPES
are the possible outcomes? Show all ratios of genotypes and phenotypes.
5. In fruit flies black eyes (B) is
dominant to red eyes (b). If a
hybrid black eyed fly is
crossed with a red eyed fly,
what are the possible
outcomes? Show all ratios of
genotypes and phenotypes.
6. Cleft chins (C) are dominant
over smooth chins (c). What
if two heterozygous parents
were crossed? What would
the possible outcomes be?
Show all ratios of genotypes
and phenotypes.
GENOTYPES
PHENOTYPES
GENOTYPES
PHENOTYPES
TO FIGURE THE QUESTIONS OUT IN YOUR HEAD FIRST, AND THEN USE A PUNNETT SQUARE TO
TEST YOUR ANSWER.
7. Huntington’s Disease is a dominant genetic disorder. If a hybrid person (Hh) is crossed with
a normal person (hh), what is the probability that their offspring will have Huntington’s
Disease?
8. Yapping is a trait controlled by a dominant allele (Y) and is uncommon in some populations.
If two heterozygous parents (Yy) have children, what is the probability that their offspring
will be a non-yapper? What percent will yap?