Genetics Unit Test: Practice Guide Answers
Part A: Complete the following questions:
1.) What is the purpose of a punnett square? What does it show?
All possible results of a genetic cross.
The possible genotypes of the offspring.
The alleles in the gametes of each parent.
2.) What is a genotype? Genetic makeup Give an example of how it is written. GG
3.) What is a phenotype? Physical appearance Give an example of how it is written. green
4.)In a simple dominance problem involving green pea pods (green is the dominant
color), what would be two possible genotypes for green pea pods? GG or Gg Why are
they both green? the dominant trait is expressed phenotypically.
G
g
5.)In a simple dominance problem, what parental genotypes
cross to produce a 3:1 phenotypic ratio of green pea pods
G
to yellow pea pods? Draw an example to the right.
g
6.) Same punnett square as #5.
Phenotypes = 3 green: 1 yellow Genotypes = 1GG:2Gg:1gg
7.) What does homozygous mean? Two of the same alleles What are two other terms
meaning the same thing? pure or purebred
8.) What does heterozygous mean? Alleles are different What is one other terms
meaning the same thing? Hybrid
9.) What does the Law of Segregation say? When organisms reproduce, alleles separate
from each other Is there an equal chance of inheriting each allele from one
parent? yes How about the other parent? each parent contributes 50%
X
X
Draw an example punnett square using the sex chromosomes (Female =
XX, Male = XY).
Y
X
10.)Snapdragon flowers exist in three color variations; white, red, and pink. What type of
inheritance does this show? Incomplete dominance What would be the genotypes for
each of the phenotypes described above? To the right, cross a Pink flower with a Pink
flower, and give the genotypic and phenotypic ratios.
R
Red: RR, White: WW, Pink: RW
R
Genotypic Ratio: 1RR:2RW:1WW
W
W
Phenotypic Ratio: 1red:2pink:1white
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Genetics Unit Test: Practice Guide Answers
11.) What does incomplete dominance mean? Incomplete dominance involves alleles
that are not clearly dominant or recessive. The third phenotype is a blending or
intermediate of the other 2 pheontypes.
12.) What does co-dominance mean? Two dominant alleles that are expressed at the
same time.
13.) Roan cattle have a coat that has both red and white hairs appearing at the same time.
Answer the following questions using this information.
a. What is this type of inheritance called? Co-dominance
b. How is a Roan cow produced? What would be the genotypes of the parents that
would only produce Roan calf? red and white hairs intermixed in the coat of the
calf- producing red patches and white patches
c. What would be the genotypes and phenotypes of
the offspring of two roan cattle. Complete the
punnett square to the right to solve the problem.
Genotypes: _____________________________________
CR
CW
C
R
C
W
Phenotypes: 1 red, 2 roan, 1 white
14.) What is a karyotype? A picture of our chromosomes What can be observed in a
karyotype? An extra or missing chromosome[s]
15.) What is selective breeding? Specific desirable traits are chosen to reproduce Give an
example. Dogs
16.) What is genetic engineering? Taking DNA from one source & transferring it into
another living thing. Give an example of how it can be beneficial for someone who is
diabetic. Using plasmids to create recombinant DNA, it has made insulin cheaper and
more readily available.
17.) How might GMO (genetically modified organisms) crops be harmful to humans and
the environment? Genetic engineering has led to genetically modified plants that resist
insect pests and bacterial and fungal infections. This could cause unplanned ecosystem
interactions.
18.) What is gene therapy? specific gene sequences are inserted into an individuals cells
and tissues to replace a defective or mutant allele. How does it work? Use viruses to
insert specific gene sequences.
19.) What is cloning? What does the process produce? Cloning an individual usually produces
organisms that contain identical genes.
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Genetics Unit Test: Practice Guide Answers
20.) What does the Law of Independent Assortment say? Two alleles separate independently
of one another. Give an example. A certain type of flower has two alleles for color (red, white),
and two alleles for stem height (tall, short).
21.) What is a polygenic trait? Controlled by more than one gene. Give an example. Height
22.) What does it mean if a trait is sex-linked? The trait is on the sex chromosome What
chromosome are they located on? The X chromosome only
23.) Why do men more frequently suffer from sex-linked diseases? They only have one X What
does it mean for a woman to be a carrier? Woman have two X chromosomes, so one could be
normal & the other could have the trait
24.) What is PKU? an inherited disorder that increases the levels of a substance called
phenylalanine in the blood. How is it inherited? recessive Show a cross between two H
heterozygous parents that do not have PKU.
H
h
h
Part B: Use the table to solve the following blood type problems:
25.) A Mother with type A blood has offspring with a Father with type O blood. Complete
two punnett squares to find the probability that their children will have type B blood.
IA
IA
IA
i
i
i
IA i
IA i
i i
IA i
IA i
IA i
i i
i
i
IA i
They will not have a child with type B blood!
26.)Blood type is inherited through multiple, codominant alleles, including IA, IB, and i. A
child has type B blood. If the father has type AB blood, what are all the possible
phenotypes of the mother? A, B, AB, or O
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Genetics Unit Test: Practice Guide Answers
27.) There has been a mix-up at the hospital, and the staff is attempting to make sure that
the babies have made it home with their appropriate parents. Sheryl has type A blood,
AA or AO and her husband Steve has type B blood, BB or BO. Please make both
appropriate punnett squares to show if their “baby” who has type O blood is definitely
their baby.
A
O
B
O
Part C: Use the pedigree to answer the following questions:
28.)What is a pedigree used for?
Determine whether a trait is inherited.
Show how a trait is passed from one generation to the next.
Determine whether an allele is dominant or recessive.
29.)What do the squares represent? Males
30.)What do the circles represent? Females
31.)What does a shaded circle or square indicate? They have the trait
32.)How many generations are shown? 3
33.)How many children did the original parents have? 4
34.)How many males are there in the third generation? 5
35.)How many individuals are colorblind in this pedigree? 2
36.)How many individuals are carriers in this pedigree? 4
37.)How will you study differently for this exam? What study strategies will you use?
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