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Genetics Practice Problems
Name ___________________________________
Use Punnett squares to support all answers.
1. Use a Punnett square to determine all of the offspring’s genotype and phenotype
frequencies from the following crosses. “R” is the dominant allele, specifying
round seeds in pea plants. “r” is the recessive allele for wrinkled seeds.
a) Rr X Rr
b) Rr X rr
c) RR X rr
2. Sheep exist in white or black fur color. A white ewe mates with a white ram and
produces a black lamb. What is the dominant trait? What is the chance that
another black lamb could be produced from these parents?
3. Albinism in humans is a recessive trait. Two non-albino parents have five
children. Four are normal and one is an albino. Determine the genotypes of the
parents and all five children.
4. Achonodroplasia is a form of dwarfism inherited as a dominant trait. Inheriting
two dominant alleles is fatal at birth. Two dwarfs have a child that is a dwarf and
later a child that is of normal height. What are the parent’s genotypes? What is
the probability of having a third child that is of normal height?
Genetics Practice Problems
Name ___________________________________
5. A brown mouse is mated with two female black mice. After several generations
the first female has had 48 black mice and 0 brown. The second female has had 4
black and 11 brown offspring. What pattern of inheritance controls the coat-color
in mice? Give the genotype of the three parents and support your answer.
6. In humans, brown eyes are dominant over blue. If a blue-eyed man has children
with a brown-eyed woman (whose father has blue eyes), what percentage of their
children would you predict will have blue eyes?
7. A man has six fingers on each hand. His wife and first-born child have normal
digits but the other six children have a sixth finger. The man’s father has a sixth
finger as well but not his mother. What pattern of inheritance does the extra digit
(polydactyly) follow? What is the dominant trait and what is the recessive trait.
8. Male pattern baldness is a controlled by a gene on the X chromosome. If a man
who is not bald has children with a woman suffering from pattern baldness, what
are the chances that their sons would also be bald? Their daughters?
Genetics Practice Problems
Name ___________________________________
9. In Mexican Hairless dogs, hairless is dominant over normal hair. If heterozygous
Mexican Hairless dogs are interbred, the puppies show a ratio of 2/3 hairless to
1/3 normal hair. In addition, some of the puppies are born dead and deformed.
Propose an explanation for this outcome and outline how you could test your
hypothesis.
10. In a maternity ward, four babies become accidentally mixed up. The blood types
of the children are O, AB, A and B respectively. Indicate which sets of parents’
matches each child.
a) AB X O
b) A X O
c) A X AB
d) O X O
11. A woman with a rare (and hypothetical) disease called bent fingers has children
with a normal man. All of their sons and none of their daughters have bent
fingers. What is the pattern of inheritance for this condition? Why do the
daughters not have bent fingers? Will the daughter’s future children have bent
fingers? Explain.
12. A male parent has type B blood (his mother has type O) and a female parent has
type A blood (her father has type B). Predict the blood types that their future
children could inherit.
Genetics Practice Problems
Name ___________________________________
13. Yellow guinea pigs crossed with white ones always produce cream-colored
offspring. Mating two cream-colored guinea pigs produced yellow, cream and
white offspring in the ratio of 25% yellow, 50% cream and 25% white. Explain
how these fur colors are inherited. List the genotypes of each color of guinea pig.
14. Suppose a father and mother claim they were given the wrong baby at the
hospital. Both parents are blood type A. The baby they have been given is blood
type O. Were they given the wrong child? What evidence do you have to prove
or disprove this?
15. An X-linked recessive gene produces a blood clotting disorder called hemophilia.
A normal woman whose father was a hemophiliac has children with a man that
has hemophilia.
a) What are the possible genotypes for the mother of the hemophiliac man?
b) What are the chances that the first child from this mating will be a boy
with hemophilia?
c) Of the girls produced by these parents, what percentage can be expected to
have hemophilia?
d) Of all the children (gender unspecified) of these parents, what proportion
can be expected to have normal blood clotting ability?