Genetics Practice Problems and Solutions for AP Biology

Genetics Practice Problems and Solutions for AP Biology

Genetics practice problems focus on concepts such as incomplete dominance, co-dominance, and sex-linked traits. This key provides detailed solutions to various genetics scenarios, including blood type inheritance and traits in cattle. Ideal for AP Biology students preparing for exams, it includes Punnett squares and genotype-phenotype ratios. The practice problems cover essential genetic principles and real-world applications, making it a valuable resource for mastering genetics.

Key Points

  • Explains incomplete dominance with radish color inheritance examples.
  • Covers co-dominance in blood types, detailing genotype frequencies.
  • Includes sex-linked trait analysis, particularly hemophilia inheritance.
  • Provides Punnett square solutions for various genetic crosses.
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Name _____________________________ Period _________
AP Biology Date ______________________
1 of 3
Developed by Kim B. Foglia • www.ExploreBiology.com • ©2008
GENETICS PRACTICE 2: BEYOND THE BASICS
Solve these genetics problems. Be sure to complete the Punnett square to show how you
derived your solution.
INCOMPLETE DOMINANCE
1. In radishes, the gene that controls color exhibits incomplete dominance. Pure-breeding red
radishes crossed with pure-breeding white radishes make purple radishes. What are the
genotypic and phenotypic ratios when you cross a purple radish with a white radish?
50% purple (RW)
50% white (WW)
R
W
W
RW
WW
W
RW
WW
2. Certain breeds of cattle show incomplete dominance in coat color. When pure breeding red
cows are bred with pure breeding white cows, the offspring are roan (a pinkish coat color).
Summarize the genotypes & phenotypes of the possible offspring when a roan cow is mated
with a roan bull
25% red (RR)
50% roan (RW)
R
W
R
RR
RW
W
RW
WW
25% white (WW)
CO-DOMINANCE
3. A man with type AB blood marries a woman with type B blood. Her mother has type O
blood. List the expected phenotype & genotype frequencies of their children.
25% type AB blood (I
A
I
B
)
50% type B blood (I
B
I
B
& I
B
i)
I
B
I
A
I
B
I
B
I
B
i
I
A
i
I
B
i
25% type A blood (I
A
i)
Name _____________________________ AP Biology
2 of 3
4. The father of a child has type AB blood. The mother has type A.
Which blood types can their children NOT have? _______________________
5. A woman with type A blood and a man with type B blood
could potentially have offspring with what blood types? _______________________
6. The mother has type A blood. Her husband has type B blood.
Their child has type O blood. The father claims the child can’t
be his. Is he right? _______________________
7. The mother has type B blood. Her husband has type AB blood.
Their child has type O blood. The father claims the child can’t
be his. Is he right? _______________________
8. The mother has type AB blood. The father has type B blood.
His mother has type O blood. What are all the possibilities of
blood type for their children? _______________________
LETHAL DOMINANT
9. Achondroplasia (dwarfism) is caused by a dominant gene. A woman and a man both with
dwarfism marry. If homozygous achondroplasia results in death of embryos, list the
genotypes and phenotypes of all potential live-birth offspring
50% dwarfism (Aa)
25% normal (aa)
What is the expected ratio of dwarfism to
normal offspring?
A
AA
Aa
a
Aa
aa
67% dwarfism : 33% normal
SEX-LINKED
10. The genes for hemophilia are located on the X chromosome. It is a recessive disorder. List
the possible genotypes and phenotypes of the children from a man normal for blood clotting
and a woman who is a carrier. (HINT: You have to keep track of what sex the children are!)
50% females normal
50% females carrier
50% males normal
X
H
X
H
X
H
X
H
Y
X
h
X
H
X
h
X
h
Y
50% males hemophilia
EXTRA CREDIT: Remember those roan cows from question 2? They also have a second gene
for horn vs. hornless cattle. The allele for horns dominates the allele for hornless. If a bull and
cow are heterozygous for both genes, what are the probabilities for each possible phenotype?
I
A
_ x I
A
I
B
= no O
I
A
_ x I
B
_ = AB, A, B, O
No! I
A
_ x I
B
_ = AB, A, B, O
Yes! I
B
_ x I
A
I
B
= AB, A, B
I
A
I
B
x I
B
i = AB, A, B
Name _____________________________ AP Biology
3 of 3
Solving it the short (probability) way:
R
RR
Rr
r
Rr
rr
h
H
HH
Hh
h
Hh
hh
Red, horn → RR x H_ = ¼ x ¾ = 3/16
Roan, horn → Rr x H_ = 2/4 x ¾ = 6/16
Red, no horn → RR x hh = ¼ x ¼ = 1/16
Roan, no horn → Rr x hh = 2/4 x ¼ = 2/16
White, horn → rr x H_ = ¼ x ¾ = 3/16
White, no horn → rr x hh = ¼ x ¼ = 1/16
Solving it the long way:
RH
Rh
rH
rh
RH
RRHH
red, horn
RRHh
red, horn
RrHh
roan, horn
RrHh
roan, horn
Rh
RRHh
red, horn
RRhh
red, no horn
RrHh
roan, horn
Rrhh
roan, no horn
rH
RrHH
roan, horn
RrHh
roan, horn
rrHH
white, horn
rrHh
white, horn
rh
RrHh
roan, horn
Rrhh
roan, no horn
rrHh
white, horn
rrhh
white, no horn
RRH_
red, horn: 3/16
RrH_
roan, horn: 6/16
RRhh
red, no horn: 1/16
Rrhh
roan, no horn: 2/16
rrH_
white, horn: 3/16
rrhh
white, no horn: 1/16
Usually your 9/16 if red showed
simple dominance to white
⎬
Usually your 3/16 if red showed
simple dominance to white
⎬
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End of Document
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FAQs of Genetics Practice Problems and Solutions for AP Biology

What is incomplete dominance in genetics?
Incomplete dominance occurs when the phenotype of heterozygotes is intermediate between those of the two homozygotes. For example, in radishes, crossing red and white pure-breeding plants results in purple radishes. This illustrates how alleles interact to produce a blended phenotype rather than one being completely dominant over the other.
How does co-dominance affect blood type inheritance?
Co-dominance occurs when both alleles in a heterozygote are fully expressed, resulting in a phenotype that displays characteristics of both alleles. In human blood types, a person with type AB blood has both A and B antigens expressed. This genetic interaction is crucial for understanding blood transfusions and compatibility.
What are the possible blood types from an AB and B cross?
When a man with type AB blood marries a woman with type B blood, their children can inherit blood types A, B, or AB. The possible genotypes include IAIB (AB), IBi (B), and IAi (A). This genetic combination highlights the importance of understanding inheritance patterns in human blood types.
What is the significance of sex-linked traits like hemophilia?
Hemophilia is a recessive disorder linked to the X chromosome, affecting blood clotting. In a cross between a normal man and a carrier woman, potential offspring can be affected by the disorder. Understanding sex-linked inheritance is vital for predicting the likelihood of such genetic conditions in families.

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