Monohybrid Crosses
Practice Exercises
Complete the following Punnett Squares for the questions below. Find the genotype as well as the phenotype
ratios for the possible offspring.
Question 1: Long haired fur is dominant to short haired fur in dogs. Show a cross between a purebred
homozygous long haired dog and a purebred homozygous short haired dog. Use the following template as a
guide.
P generation:
LEGEND
Homozygous long Heterozygous long Homozygous short -
__________ X __________
Results of a _____ x _____ cross
F1 genotypes:
F1 phenotypes:
Question 2: Show a cross between a heterozygous (hybrid) long haired dog with a purebred short haired dog.
Question 3: Solid Green watermelon skin is dominant to striped watermelon skin. Show a cross between a
heterozygous solid green watermelon and a homozygous striped watermelon. Find the possible offspring.
Question 4: Black guinea pigs are dominant to white guinea pigs. Find the possible offspring produced as a
result of a cross between a hybrid (heterozygous) black guinea pigs and another hybrid (heterozygous) black
guinea pig.
Question 5: Tongue rolling is dominant in humans over non tongue rolling. Show a cross between a
homozygous tongue roller and a homozygous non tongue roller. Find the possible offspring.
Question 6: Red eyes are dominant to white eyes in fruit flies. Find the ratio of the offspring produced in the
following fruit fly cross: Hybrid red eyes with purebred white eyes.
Question 7: In humans, unattached earlobes are dominant to attached earlobes. Find the result for the offspring
produced between heterozygous unattached earlobes with another who is also heterozygous for unattached
earlobes.
Question 8: Round seeds are dominant to wrinkled seeds in pea plants. Find the results when a hybrid round
seed plant is crossed with a pure trait wrinkle seed plant.
Question 9: White flowers are recessive to red flowers some species of carnations. Show a cross between two
white flowering plants.
Question 10: Curly hair is dominant to straight hair in humans. Show a cross between a heterozygous curly
haired parent with a pure homozygous straight haired parent.
Bikini Bottom – Dihybrid Crosses
Name ________________________________
Use the chart to identify the genotypes of the following traits:
1. Heterozygous round eyes, blue body ________
2. Hybrid eye shape, purebred roundpants ________
3. Purebred roundpants, heterozygous long nose ________
Trait
Body Shape
Body Color
Eye Shape
Nose Style
Dominant Gene
Squarepants (S)
Yellow (Y)
Round (R)
Long (L)
Recessive Gene
Roundpants (s)
Blue (y)
Oval (r)
Stubby (l)
4. SpongeBob’s aunt, who is a roundpants, has a cute stubby nose. She has finally found the sponge of her dreams
and is ready to settle down. Her fiancé always comments on how adorable her nose is (he says it reminds him of his
mother’s – aww, how sweet!). They wonder what the chances are of that trait being passed on. Her fiancé is a
purebred squarepants and is a hybrid for his long nose.
A. Identify the genotypes of the aunt and her fiancé.
Aunt = Roundpants, Stubby Nose = ________
Fiancé = Purebred Squarepants, Long Nose = ________
B. What are the possible gamete combinations for each person?
Aunt = ______________________________
Fiancé = ______________________________
C. What are the possible genotypes for their children? ______________________________________
5. As we know, SpongeBob is heterozygous for his yellow body color and his squarepants, while his wife
SpongeSusie is blue and has roundpants. Use this information to answer the following questions.
A. Give the genotypes for each.
SpongeBob = __________________
SpongeSusie = _______________
B. What are the possible gamete combinations for each person?
SpongeBob = __________________
SpongeSusie = __________________
C. Complete the Punnett square based on the information provided in #5.
____________
____________
____________
____________
____________
____________
____________
____________
D. Answer the questions based on your Punnett square.
What is the chance of a blue baby? _____
What is the chance of a blue squarepants? _____
What is the chance of a squarepants? _____
What is the chance of a purebred recessive for both traits? _____
Contributed by Andrea Stonebraker
6. In starfish, pink body color (P) is dominant to orange (p), and thick eyebrows (T) are dominant over thin (t)
ones. Patrick, who is heterozygous for body color but purebred for thick eyebrows, has met Patti, who is recessive
for both traits.
A. What is Patti’s phenotype? _______________________________
B. Is it possible for the new couple to have offspring that resemble their mother? Explain.
___________________________________________________________________________
___________________________________________________________________________
C. Before Patrick commits to this relationship, he would like to guarantee that his offspring
would have his thick eyebrows as he thinks they make him smarter! You need to provide
evidence for or against the marriage with regards to eyebrows ONLY.
7. While Squidward’s family boasts about being a purebred line for dominant light
blue skin color, they are also purebred for a less distinguished trait: the recessive
trait of baldness. Lack of hair causes Squidward some self-esteem issues that he
does not want his children to face. He would like to ensure that his offspring have
hair AND with his blue skin color. What traits should he look for in a bride?
A. Must she have hair? Explain. _____________________________________________
_______________________________________________________________________
B. Must she be blue? Explain. _______________________________________________
________________________________________________________________________
Squidward Traits:
Skin Color
Blue = B, Green = b
Hair
Hair = H, Bald = h
C. Squidward has found a potential bride prospect with the green squid Octavia. While Octavia has
does not. Determine the chances of their child being blue and having hair.
hair, her father
Squidward's Genotype = __________ Octavia's Genotype = __________
D. Use the genotypes in above to complete the Punnett square below and then answer the questions.
____________
____________
____________
____________
____________
____________
____________
E. Answer these questions based on your Punnett square.
For which traits, if any, is it possible for their offspring to be purebred?
What is the probability of their children being heterozygous for both traits? ________
Contributed by Andrea Stonebraker
____________
Bikini Bottom Genetics
Incomplete Dominance
Name ________________________________
SpongeBob loves growing flowers for his pal Sandy! Her favorite flowers, Poofkins, are found in red,
blue, and purple. Use the information provided and your knowledge of incomplete dominance to
complete each section below.
1. Write the correct genotype for each color if R represents a red gene and B represents a blue gene.
Red - _____
Blue - ______
Purple - _____
2. What would happen if SpongeBob crossed a Poofkin with red flowers with a Poofkin with blue flowers.
Complete the Punnett square to determine the chances of each flower color.
(a) Give the genotypes and phenotypes for the offspring.
(b) How many of the plants would have red flowers? _____%
(c) How many of the plants would have purple flowers? _____ %
(d) How many of the plants would have blue flowers? _____ %
3. What would happen if SpongeBob crossed two Poofkins with purple flowers? Complete the Punnett
square to show the probability for each flower color.
(a) Give the genotypes and phenotypes for the offspring.
(b) How many of the plants would have red flowers? _____%
(c) How many of the plants would have purple flowers? _____ %
(d) How many of the plants would have blue flowers? _____ %
4. What would happen if SpongeBob crossed a Poofkin with purple flowers with a Poofkin with blue
flowers? Complete the Punnett square to show the probability for plants with each flower color.
(a) Give the genotypes and phenotypes for the offspring.
(b) If SpongeBob planted 100 seeds from this cross, how many should he
expect to have of each color?
Purple flowers - ______ Blue flowers - ______ Red flowers - ______
SpongeBob and his pal Patrick love to go jellyfishing at Jellyfish Fields! The fields are home to a
special type of green jellyfish known as Goobers and only really great jellyfishermen are lucky enough
to catch some on every trip. Many of the jellyfish are yellow (YY) or blue (BB), but some end up green
as a result of incomplete dominance. Use this information to help you complete each section below.
5. What would happen if SpongeBob and Patrick crossed two “goobers” or green jellyfish? Complete the
Punnett square to help you determine the probability for each color of jellyfish.
(a) Give the possible genotypes and phenotypes for the offspring.
(b) What percentage of the offspring would be yellow? _____%
(c) What percentage would be blue? _____ %
(d) What percentage would be “goobers” (green)? _____ %
6. What would happen if they crossed a yellow jellyfish with a goober? Complete the Punnett square to help
you determine the probability for each color of jellyfish.
(a) Give the possible genotypes and phenotypes for the offspring.
(b) What percentage of the offspring would be yellow? _____%
(c) What percentage would be blue? _____ %
(d) What percentage would be “goobers” (green)? _____ %
7. What would happen if they crossed a blue jellyfish with a yellow jellyfish? Complete the Punnett square
to help you answer the questions.
If 100 jellyfish were produced from this cross, how many would you
expect for each?
Yellow - _____
Blue - _____
Goobers - ______
8. What would happen if they crossed a blue jellyfish with a goober? Complete the Punnett square to help
you answer the questions.
If 100 jellyfish were produced from this cross, how many would you
expect for each?
Yellow - _____
Blue - _____
Goobers - ______
Codominance Worksheet (Blood types)
Name ______________________________
Human blood types are determined by genes that follow the CODOMINANCE pattern of inheritance. There are two
dominant alleles (IA and IB) and one recessive allele (i).
Blood Type (Phenotype)
Genotype
O
ii
AB
A
B
1.
Can donate blood to:
A,B,AB and O
(universal donor)
IAIB
IAIA or
IAi
B
B
I I or IAi
O, AB
AB, A
AB,B
Can receive blood from:
O
A,B,AB and O
(universal receiver)
O,A
O,B
Write the genotype for each person based on the description:
a.
b.
c.
d.
e.
f.
g.
Homozygous for the “B” allele
Heterozygous for the “A” allele
Type O
Type “A” and had a type “O” parent
Type “AB”
Blood can be donated to anybody
Can only get blood from a type “O” donor
______
______
______
______
______
______
______
2.
Pretend that Brad Pitt is homozygous for the type B allele, and Angelina Jolie is type “O.” What are all the
possible blood types of their baby?
3.
Draw a Punnett square showing all the possible blood types for the offspring produced by a type “O” mother
and an a Type “AB” father
4.
Mrs. Clink is type “A” and Mr. Clink is type “O.” They have three children named Matthew, Mark, and
Luke. Mark is type “O,” Matthew is type “A,” and Luke is type “AB.” Based on this information:
a. Mr. Clink must have the genotype ______
b. Mrs. Clink must have the genotype ______ because ___________ has blood type ______
c. Luke cannot be the child of these parents because neither parent has the allele _____.
5.
Two parents think their baby was switched at the hospital. Its 1968, so DNA fingerprinting technology does
not exist yet. The mother has blood type “O,” the father has blood type “AB,” and the baby has blood type
“B.”
a. Mother’s genotype: _______
b. Father’s genotype: _______
c. Baby’s genotype: ______ or ________
d. Punnett square showing all possible genotypes for children produced by this couple
e. Was the baby switched?
Two other parents think their baby was switched at the hospital. The mother has blood type “A,” the father
has blood type “B,” and the baby has blood type “AB.”
a. Mother’s genotype: _______ or ________
b. Father’s genotype: _______ or ________
c. Baby’s genotype: ______
d. Punnett square that shows the baby’s genotype as a possibility:
e. Was the baby switched?
Based on the information in this table, which man could not be the father of the baby? Justify your answer
with a Punnett square.
6.
7.
Name
Mother
Baby
Blood Type
Type A
Type B
Sammy the player
George the sleeze
The waiter
The cable guy
Type O
Type AB
Type A
Type B
8.
Explain why blood type data cannot prove who the father of a baby is, and can only prove who the father is
not.
Codominance Worksheet (Blood types)
Name ______________________________
Human blood types are determined by genes that follow the CODOMINANCE pattern of inheritance. There are two
dominant alleles (IA and IB) and one recessive allele (i).
Blood Type (Phenotype)
Genotype
O
ii
AB
A
B
1.
Can donate blood to:
A,B,AB and O
(universal donor)
IAIB
IAIA or
IAi
B
B
I I or IAi
O, AB
AB, A
AB,B
Can receive blood from:
O
A,B,AB and O
(universal receiver)
O,A
O,B
Write the genotype for each person based on the description:
a.
b.
c.
d.
e.
f.
g.
Homozygous for the “B” allele
Heterozygous for the “A” allele
Type O
Type “A” and had a type “O” parent
Type “AB”
Blood can be donated to anybody
Can only get blood from a type “O” donor
______
______
______
______
______
______
______
2.
Pretend that Brad Pitt is homozygous for the type B allele, and Angelina Jolie is type “O.” What are all the
possible blood types of their baby?
3.
Draw a Punnett square showing all the possible blood types for the offspring produced by a type “O” mother
and an a Type “AB” father
4.
Mrs. Clink is type “A” and Mr. Clink is type “O.” They have three children named Matthew, Mark, and
Luke. Mark is type “O,” Matthew is type “A,” and Luke is type “AB.” Based on this information:
a. Mr. Clink must have the genotype ______
b. Mrs. Clink must have the genotype ______ because ___________ has blood type ______
c. Luke cannot be the child of these parents because neither parent has the allele _____.
5.
Two parents think their baby was switched at the hospital. Its 1968, so DNA fingerprinting technology does
not exist yet. The mother has blood type “O,” the father has blood type “AB,” and the baby has blood type
“B.”
a. Mother’s genotype: _______
b. Father’s genotype: _______
c. Baby’s genotype: ______ or ________
d. Punnett square showing all possible genotypes for children produced by this couple
e. Was the baby switched?
Two other parents think their baby was switched at the hospital. The mother has blood type “A,” the father
has blood type “B,” and the baby has blood type “AB.”
a. Mother’s genotype: _______ or ________
b. Father’s genotype: _______ or ________
c. Baby’s genotype: ______
d. Punnett square that shows the baby’s genotype as a possibility:
e. Was the baby switched?
Based on the information in this table, which man could not be the father of the baby? Justify your answer
with a Punnett square.
6.
7.
Name
Mother
Baby
Blood Type
Type A
Type B
Sammy the player
George the sleeze
The waiter
The cable guy
Type O
Type AB
Type A
Type B
8.
Explain why blood type data cannot prove who the father of a baby is, and can only prove who the father is
not.
Lethal alleles Worksheet
Name ______________________________
Alleles that cause an organism to die only when present in homozygous condition are called lethal
alleles.
1. Cystic fibrosis is caused by a recessive lethal gene and can be detected by an excess
concentration of chloride in sweat. If a sweat test reveals a man to be heterozygous and
his wife to be homozygous normal, what are the chances that their children will have the
disease? Could any of their grandchildren have the disease?
2. In humans, sickle-cell anemia is caused by a recessive lethal allele Hbs; individuals
who are HbaHbs have sickle-cell trait, but are healthy.
a. What is the probability of two heterozygous individuals giving birth to a child with
sickle-cell trait?
b. What is the probability of two heterozygous individuals giving birth to a child with
sickle-cell anemia?
c. If a normal HbaHba individual receives a blood transfusion from a HbaHbs individual
(heterozygous for sickle cell) what are the chances that the HbaHba man and his HbaHba
wife will have HbaHbs children?
3. Albinism in corn plants is caused by a recessive lethal gene that results in death before
maturity. What will the adult phenotypic ratio be for the F1 generation of heterozygous
parents?
4. Huntington's chorea is a dominant lethal in humans. The disease does not appear until
later in life, so that afflicted individuals may already have produced children. What are
the F1 genotypic and phenotypic ratios of parents who are homozygous dominant and
heterozygous?