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Genetics Practice Problems
Name:___________________________
Problem set #1 -Monohybrid
1. A man with neurofibromatosis ( a dominant (Nn) condition that causes growths on nerves) has a
child with a woman who does not have the condition and absolutely no history of it in her family.
What is the probability of their child having neurofibromatosis? Use a punnett square to prove
your answer.
2. Streptomicrodactyly, crooked little fingers, is dominant to the normal situation in humans. A man
with normal little fingers marries a woman with crooked little fingers, but whose mother had straight
little fingers. Complete a punnett square and give the genotypic and phenotypic ratios of the expected
offspring.
3. Tay Sachs disease is a lethal recessive disorder most common in certain populations of Jewish
people. A child born with Tay Sachs has two normal parents. What must be their genotypes?
Explain.
4. In guinea pigs, the gene for black coat is dominant over that for white coat. If a homozygous,
black-coated male is crossed with a white-coated female, what color of coat would you expect in
the first (f1) generation? What are the genotypic and phenotypic ratios?
5. a. If you flip a coin 150 times, what would the expected frequency of “heads” be?
b. Would your observed results equal this expected frequency?
6. There is a 50:50 chance of producing a child of either sex. What is the probability of having 3
girls in a row? (Show your work)
Problem Set #2 – Dihybrid Cross
1. Explain in your own words what Mendel’s law of independent assortment states:
2. What is a dihybrid cross?
In Rabbits, long fur (L) is dominant to short fur (l) and Floppy Ears (F) are dominant over straight (f)
ears. Two heterozygous, long fur – floppy ear rabbits are crossed. Find the expected genotypes and
phenotypes.
a. What are the genotypes of both parents? __________ and ___________
b. What are the possible gametes from each parent?
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How many offspring will be:
c. long and floppy? ________________
d.
long and straight? ________________
e.
short and floppy? _______________
f.
short and straight ________________
3. Cross a Long(LL) fur / straight ear rabbit with a heterozygous individual for both traits.
a. What are the genotypes of the parents? ___________ and _____________
b. What are the possible gametes for the parents?
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c. What is the genotypic ratio:
d. What is the phenotypic ratio:
Problem Set #3
Name: ________________
Incomplete Dominance
1. What is an incomplete dominant trait?
Snapdragon flowers are often found in a variety of colors. No color is dominant over another. Use the
following genotypes to solve the next set of questions.
2. Cross a pink snapdragon with a white snapdragon
Genotypes
Phenotypes
a. Parents ______________x _______________
RR
RED
b. G ratio = ________________
WW
WHITE
c. P ration = ________________
RW
Pink
d. % white = ________________
e. % Red = ________________
f. % Pink = ________________
3. Cross a red snapdragon with a pink snapdragon
a. Parents ______________x _______________
b. G ratio = ________________
c. P ration = ________________
d. % white = ________________
e. % Red = ________________
f. % Pink = ________________
4. If we obtain a phenotypic ratio of one red to one white to two pink, what color were
the parents? Explain:
Problem set # 4 -Co-dominance
1. What is Codominance?
In horses, chestnut and white coat colors are codominant. Heterozygous horses have a blend of both
colors, which is a golden tan color. Such heterozygous horses are known as palominos (like Mr. Ed).
Define the trait:
HWHW –
HB H B HWHB –
2. Cross a palomino horse with a white horse
Parents _____________ x ________________
Genotypic ratio:
Phenotypic ratio:
2. What color horses would you have to breed in order to have three different colored offspring?
Explain your answer and prove with a punett square.
Problem Set #5 – Multiple Alleles
1. What are multiple alleles?
Blood type is determined by multiple alleles. Complete the following chart for possible blood types.
Phenotype
Antiobodies
A Blood
Antigen in Blood
cells
A
B
% distribution in
US
42
B Blood
B
A
7
A and B
None
2
none
A and B
48
AB Blood
O Blood
Genotype
2. Mixing blood from two individuals can lead to blood clumping or agglutination. The clumped red
cells can crack and cause toxic reactions. This can have fatal consequences. The transfusion will work if
a person who is going to receive blood has a blood group that doesn't have any antibodies against the
donor blood's antigens. But if a person who is going to receive blood has antibodies matching the donor
blood's antigens, the red blood cells in the donated blood will clump.
a. What blood type is the universal donor? _______________
b. What blood type is the universal recipient? ________________
c. A type A blood person can donate to __________________________
3. Suppose two newborn babies were accidentally mixed in the hospital, and their was a question of
which baby belonged to which parents. From the following blood types, determine which baby belongs
to which parents. Explain your answer
Baby 1 = Type 0
Mrs. Brown = Type B
Baby 2 = Type A
Mr. Brown = Type AB
Mrs. White = Type B
Mr. White = Type B
4. One Parent has Type A Blood. The other parent has type B blood. What are their genotypes if they
produce many children whose blood types are: Prove your answers
a. All AB
b. ½ AB and ½ B
c. ¼ O
5. The following is an edited version of email exchange that occurred in response to the a human
genetics tutorial on a biology website.
First message from a concerned grandmother:
I am wondering how to find out blood type of my grandson…. My daughter has A blood…. The father is
in questions and she is stressed to the max on the father of the baby boy.
a. What is the most common blood type?
Answer to the first message by Professor Hallick:
Blood type analysis can occasionally rule out a potential faterh (i.e. if the mother is type A and the child
is type ) the father could not be type AB, but could be type A, B, or O), but is not a metho the can be used
to establish paternity. If the paternity of your grandson needs to be established for legal reasons, such as
establishing responsibility for child support, a DNA test would be the accepted method. There are
commercial laboratories that will do the test for a fee. Blood samples would be required from the
mother, child and any of the alleged father.
Second Messange from grandmother:
Thanks so much for your prompt reply. Here is the scenario…. Paternity isn’t going to be established…
it is going to lay…for lack of a better expression. My daughter is Type A, my grandson is B, we don’t
know how the types of the two gentlemen in question…. My question is what are the types that the
fathers would have to be in order for my grandson to be type B?
What is the correct answer to the grandmother’s question? Explain your answer to grandma.
6. (True Story) In Denmark, a husband and wife who had been unsuccessfully trying to have a baby went
to a fertility clinic. Sperm and eggs were collected from father and mother, and combined in a petri dish,
creating several "test-tube babies". These babies were implanted in the mother and 9 months later she
delivered twins, one with light skin and one with dark skin. Because this seemed strange, a DNA test was
conducted and it was found that both children were related to the mother, but only the light skinned child
was related to the father. What must have happened?
Problem Set # 6 – Sex Linked and sex influenced Inheritance:
1. Compare a sex linked trait to a sex influenced trait. Give an example of each.
2. A young married couple is anxiously awaiting the birth of their first child. What are the chances they
have a boy?
3. Five years later the couple is awaiting the birth of their 5th child. They found out, through an ultrasound, that they are having their fifth daughter. What are the odds of having five daughters?
In humans a sex-linked recessive gene causes color-blindness. The gene is carried on the X chromosome.
A human female must have tow recessive genes for color-blindness before she is colorblind. The human
male only need one gene for color blindness to be color-blind.
4. What is the genotype for a carrier female: ______________
5. What is the genotype for a normal vision male: ______________
6. Cross a carrier female with a normal vision male.
a.
b.
c.
d.
e.
How many normal vision females? ________
How many normal vision males? _______
How many carrier females? _______
How many colorblind males? _______
How many colorblind females? _____
7. If a father is colorblind and the mother is homozygous normal vision. Prove your answer with a
punnett square.
a. What are the odds of having a colorblind son? ____________
b. What are the odds of having a colorblind daughter?___________
c. What are the odds of having a carrier daughter? ____________
8. Webbed toes are dominant in humans. The gene for webbed toes is carried on the Y chromosome. If
a normal woman marries a man with webbed toes, what proportion of the children will have webbed
toes?
a. female % ______________
b. male % _______________
9. A dairy farmer and a geneticist were looking out the farmer’s living room window and saw a
mahogany colored Ayrshire cow with a newly born red calf. The farmer wanted to know the sex of the
calf, and the geneticist told him it was obvious from the color of the calf which sex it was. He explained
that in Ayrshire cattle, the genotype AA is mahogany and aa is red. The genotype Aa is mahogany in
males and red in females. What sex did the geneticist say the calf is? Explain your reasoning
Early balding (pattern baldness) in humans. Heterozygous men (b+/b) lose their hair; heteroyzgous
women do not have significant hair loss. Homozygous men or women (b/b) become bald. The trait is
therefore dominant in men, recessive in women. (We used b to designate the mutant baldness allele even
though the allele is dominant in males.)
10. If two individuals heterozygous for the pattern baldness allele have children, what proportion of
males will lose their hair? what proportion of females will lose their hair?
11. Is it true that if your grandfather on your mother side was bald (Bb), you will be bald? Assume your
father is not bald. Prove your answer with a punnett square.
Problem Set # 7 - Pedigrees
Name: _______________________
1. Why are pedigrees useful in biology class?
2. What symbols are used to represent the following individuals?
a. Normal female
b. Normal Male
c. Carrier female
d. affected male
e. affected female
3. At the last Mechenich family reunioun, Mr. Mechenich brought is vial of PTC paper and had everyone
taste it. What a blast we had! The following pedigree shows the Mechenich Family tree for the trait of
PTC tasting. Tasting is a dominant trait. Show the genotypes for each of the family members.
Mr. Mechenich
4. The Following pedigree shows a trait for colorblindness. Colorblindness is a sex-linked recessive trait
carried on the x chromosome. Read the pedigree and answer the following questions.
p
f1
?
a. What are the genotypes of the parents? ____________ and ________________
b. What fraction of the male offspring are colorblind?
c. What fraction of the females are colorblind?
d. Explain why males have a better chance of being colorblind.
e. What is the genotypic cross of the son in the F1 generation to his wife? _________ and ________
1. What chance do their daughters have of being colorblind? __________
2. What chance do their son’s have of being colorblind? __________
3. Are any of their son’s colorblind? Why or why not
f. What is the genotypic cross of the daughter in the F 1 generation to her husband? ______, _____
1. If they decided to have more children, what are the chances they produce a colorblind
boy?
g. How did the boys in the F3 generation end up being colorblind even though both of the parents
were not?
5. The Von Rotten family pedigree for blood types was recently discovered. Amy Von Rotten wants to
know the genotype of her blood. The phenotypes are provided.
Margaret
John
___ ___
James
Hans
___ ___
___ ___
Charlene
___ ___
John II
Eva
___ ___
___ ___
___ ___
Francine
John II
Amy
___ ___
Gertrude
___ ___
___ ___
___ ___
Ava
___ ___
Mabel
___ ___