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Genetics Review Problems: Monohybrid and Dihybrid
Complete Dominance, Incomplete Dominance, Codominance, Sex-linked, Pedigrees
These problems should be completed on a separate sheet of paper. Skip the ones you don’t know, but leave a
blank space for them so you can do them later!
1. A type of blindness known as aniridia occurs in humans and is due to an allele, A, which is dominant to the allele
for normal vision, a. Migraine headaches are due to a dominant allele, M, which is dominant to the allele for the
absence of migraine headaches, m. Each gene is found on a different pair of Autosomes. A man with normal
vision and without migraines marries a woman with normal vision and migraines. The man’s father had aniridia.
The woman’s father had normal headaches, but never a migraine.
a. Was the man’s father homozygous or heterozygous for aniridia?
b. Did the woman’s mother suffer from migraines?
c. What is the probability of this couple producing a child who is normal for both traits?
2. In humans, wavy hair (CS) results from the co-dominant situation of curly hair (C) and straight hair (S). What are
the possible results (genotypes and phenotypes and their percentages of the offspring) if a curly-haired man and
a wavy-haired woman have children?
3. Hemophilia is a sex-linked disorder. If you have the dominant gene (XH), you will have normal blood. If you have
ONLY the recessive gene (Xh), your blood will not clot. Sarah’s blood clots normally. What are all of the possible
genotypes of her parents?
4. In chimpanzees, straight fingers (F) are dominant to bent fingers (f). Complete a Punnett square to show the
genotypes and phenotypes expected for the following cross: A homozygous straight female and a homozygous
bent male?
5. What kind of surface molecule (antigen) is on type O blood?
6. In dogs, erect ears (E) is dominant over droopy ears (e). What are the results (genotypes and phenotypes and
their percentages of the offspring) if a homozygous erect dog has a litter of puppies with a heterozygous dog?
7. Tony has hemophilia, a sex-linked recessive disorder in which someone’s blood does not clot properly. One day,
he becomes angry at his parents, and blames his father, Chris, for giving him the disease. His mother, Anna,
defends Chris, saying that he can’t blame him for that.
a. Who gave Tony hemophilia: Both parents, just Anna, or just Chris?
b. Explain your answer by drawing a Punnett square and using it to support your conclusion.
8. In humans, straight toes (S) is dominant over curled toes (s). What would be the result (genotypes and
phenotypes and their percentages of the offspring) of a cross between a recessive male and a heterozygous
female?
9. What kind of antibodies does type A blood have?
10. What is a sex-linked trait?
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11. Muscular dystrophy in humans is caused by a recessive, sex-linked gene (Xm). Suppose that a woman who is a
carrier has a child with a normal man. What are the chances that the child is a…
a. Normal Female (phenotypically normal female can be a carrier)
b. Normal Male
c. Carrier Female
d. Carrier Male
e. Affected Female
f. Affected Male
12. In humans, the ability to roll your tongue (T) is dominant over not being able to roll your tongue (t). What would
be the result (genotypes and phenotypes and their percentages of the offspring) of a cross between a
heterozygous male and a homozygous recessive female.
13. Mary, who has type A blood has children with Juan, who has type B blood. They have four children: Anita
(genotype IAi), Marisa (genotype ii), Stephen (genotype IA IA), and Marc (genotype IA IB). The youngest child has
type O blood. The second-oldest has blood type A. The oldest child is from Mary’s previous marriage to Adam,
who had blood type A.
a. What is Mary’s genotype?
b. What is Juan’s genotype?
c. Arrange Mary’s children from youngest to oldest below.
14. In cattle, when a cow with Red (R) coat color and cow with White (W) coat color are mated together, the
offspring have a blended coat color that looks pink. It is called “roan.” What type of inheritance does this show?
Choose from: complete dominance, incomplete dominance, codominance, sex-linked.
15. What is the female sex chromosome called? The male sex chromosome?
16. A person with blood type A can successfully donate blood to people with which blood type(s)?
17. In Andalusian chickens, black (B) and white (W) chickens mate to make grey chickens in a pattern of inheritance
called incomplete dominance. Show a Punnett square for a cross between a grey chicken and a white chicken.
What are the expected genotypes and phenotypes and their percentages of the offspring) of the cross?
18. What does the “P” in “P generation” stand for?
19. In humans, wavy hair (CS) results from the co-dominant situation of curly hair (C) and straight hair (S). What are
the possible results (genotypes and phenotypes and their percentages of the offspring) if two curly-haired
people have children?
20. A person with blood type AB can NOT successfully donate blood to people with which blood type(s)?
21. In cats, one type of fur color is sex-linked. Gene XW produces a yellow coat, and XB produces a black coat. The
heterozygote, XBXW has a mixture of black and yellow hairs and is called a tortoise shell.
a. There are two types of inheritance going on in the example above. What are they? Choose from:
Complete dominance, Incomplete dominance, Co-dominance, Sex-linked.
b. Show a cross between a tortoise shell cat and a yellow cat. What are the results of the cross (genotypes
and phenotypes with percentages)
c. A black cat and a yellow cat have kittens. 50% of the cats produced are tortoise shell and the other 50%
are yellow male cats. What are the genotypes of the parents?
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22. What is the difference between incomplete dominance and codominance?
23. A person who has sickle cell anemia has the genotype SS and a person who does not have the sickle cell trait
has the genotype RR. This disease is inherited through incomplete dominance. What is the percent chance that
a man who is a carrier for sickle cell can have children with sickle cell disease with a woman who is normal?
24. Which blood types are:
a. Dominant?
b. Recessive?
c. Co-dominant to each other?
25. What is a “carrier”?
26. A person who can successfully donate blood to ANY person is considered the “universal donor.” Which blood
type is the universal donor? Which blood type is the universal recipient?
27. Cara, a woman who does not show any symptoms of sickle cell disease has three children with Mark, who also
does not show any symptoms of sickle cell disease. One of their children has sickle cell disease. What are the
genotypes of Cara and her husband, Mark? Genotype for Sickle Cell is SS. Genotype for Normal blood is RR.
28. What is the difference between complete dominance and incomplete dominance?
29. Can a type O father and a type AB mother have a type AB baby? Why or why not? Complete a Punnett square
to show your results.
30. Color blindness in humans is due to a recessive, sex-linked gene (Xb). A man who is normal marries a woman
who is color-blind. What are the chances of having a ….
a. Colorblind female?
b. Colorblind male?
c. Normal female? (phenotypically normal female can be a carrier)
d. Normal male?
e. Carrier female?
f. Carrier male?
31. Explain the principle of segregation using Alyssa as an example. Alyssa has freckles, and her genotype is Ff.
When Alyssa’s body makes eggs, it will use the principle of segregation. Explain this according to how it will
happen to Alyssa.
a. Alyssa also has brown eyes, genotype Bb. Explain the principle of independent assortment as it pertains
to her body making eggs.
32. When is a test-cross used?
33. What does the F in “F1” stand for?
34. How do male and female sex chromosomes look different?
35. In the jimsonweed plant, the allele for smooth seed pods, s, is recessive to the allele for spiny pods, S. At
another independently assorting locus, the allele for white flowers, w is recessive to the allele for purple flowers,
W.
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a. Two plants of unknown genotype are crossed and the following progeny result: smooth and white: 27.
spiny and white: 85. spiny and purple: 256. Smooth and purple: 93. Identify possible genotypes for the
parent plants.
b. In another cross, two plants of unknown genotype are crossed and produce the following progeny:
smooth and white: 75, spiny and white:82. Spiny and purple: 69; smooth and purple:77. Identify possible
genotypes for the parent plants.
36. Use the pedigree for Huntington’s disease below to answer the following questions. You may answer the
Pedigree questions on this paper.
a. Is the individual #1 a male or female?
b. Determine whether Huntington’s is dominant or recessive to normal (non-disease) phenotype.
c. Does individual #6 have Huntington’s or do they have a normal phenotype?
d. What is the genotype of the individual #3?
e. If individual #11 was crossed with an individual who has Huntington’s, what is the percent chance that
they will have a child with a normal phenotype? (Do a Punnett square)
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37. Use the pedigree below to answer the following questions. You may answer the Pedigree questions on this
paper.
a. Is the individual III-4 a male or female?
b. Determine whether the disease above is dominant or recessive to normal (non-disease) phenotype.
c. Does individual IV-2 have the disease or do they have a normal phenotype?
d. What is the genotype of the individual II-3?
e. If individual III-1 was crossed with individual III-6, what is the percent chance that they will have a child
with a normal phenotype? (Do a Punnett square(s))
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