EXAM 2 GENETICS PORTAGE LEARNING | ACTUAL EXAM QUESTIONS
AND ANSWERS WITH COMPLETE SOLUTIONS
Question 1
If a plant that is heterozygous for tallness (Tt) is crossed with a plant that is homozygous
recessive for shortness (tt), what is the probability that the offspring will be tall?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
Correct Answer: C) 50%
Rationale: This is a monohybrid cross. The heterozygous parent (Tt) can produce two types of
gametes: T and t. The homozygous recessive parent (tt) can only produce one type of gamete: t.
A Punnett square of this cross (Tt x tt) shows that 50% of the offspring will have the genotype Tt
(tall phenotype) and 50% will have the genotype tt (short phenotype).
Question 2
Mendel's Law of Segregation states that:
A) Alleles for different traits are passed to offspring independently of one another.
B) During gamete formation, the two alleles for a trait separate from each other, so that each
gamete receives only one allele.
C) One allele in a pair may mask the effect of the other allele.
D) Offspring will always exhibit a blend of the parents' traits.
E) Dominant alleles are always more common in a population than recessive alleles.
Correct Answer: B) During gamete formation, the two alleles for a trait separate from each
other, so that each gamete receives only one allele.
Rationale: The Law of Segregation describes what happens to the alleles for a single gene. It
explains that the two alleles an individual possesses for a trait are separated (segregated) during
meiosis, ensuring that each gamete (sperm or egg) carries only one of the two alleles.
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Question 3
A cross between two individuals that are heterozygous for two different traits (e.g., RrYy x
RrYy) is expected to produce what phenotypic ratio in the offspring, assuming independent
assortment?
A) 1:1
B) 3:1
C) 1:2:1
D) 9:3:3:1
E) 1:1:1:1
Correct Answer: D) 9:3:3:1
Rationale: This is the classic Mendelian dihybrid cross ratio. When two individuals
heterozygous for two independently assorting genes are crossed, the offspring phenotypes will
appear in a 9:3:3:1 ratio, representing the four possible combinations of dominant and recessive
traits.
Question 4
Red-green color blindness is an X-linked recessive trait. If a colorblind woman (XᶜXᶜ) has
children with a man who has normal vision (X⁺Y), what is the probability that their son will be
colorblind?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
Correct Answer: E) 100%
Rationale: A son inherits his Y chromosome from his father and one of his mother's X
chromosomes. Since the mother is colorblind, both of her X chromosomes carry the recessive
allele (Xᶜ). Therefore, any son she has must inherit one of her Xᶜ chromosomes and will be
colorblind (XᶜY).
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Question 5
In snapdragons, flower color is an example of incomplete dominance. A cross between a red-
flowered plant (CᴿCᴿ) and a white-flowered plant (CᵂCᵂ) produces pink-flowered offspring
(CᴿCᵂ). What is the expected phenotypic ratio if two pink-flowered plants are crossed?
A) 3 red : 1 white
B) 1 red : 2 pink : 1 white
C) 1 red : 1 white
D) All pink
E) 9 red : 3 pink : 1 white
Correct Answer: B) 1 red : 2 pink : 1 white
Rationale: The cross is CᴿCᵂ x CᴿCᵂ. The resulting genotypes will be in a 1:2:1 ratio: 1 CᴿCᴿ
(red), 2 CᴿCᵂ (pink), and 1 CᵂCᵂ (white). Because the heterozygous phenotype is distinct from
both homozygous phenotypes, the phenotypic ratio matches the genotypic ratio.
Question 6
The process of synthesizing an RNA molecule from a DNA template is called:
A) Translation
B) Replication
C) Transcription
D) Transformation
E) Transduction
Correct Answer: C) Transcription
Rationale: Transcription is the first step of gene expression, where the information stored in a
segment of DNA (a gene) is copied into a messenger RNA (mRNA) molecule by the enzyme
RNA polymerase.
AND ANSWERS WITH COMPLETE SOLUTIONS
Question 1
If a plant that is heterozygous for tallness (Tt) is crossed with a plant that is homozygous
recessive for shortness (tt), what is the probability that the offspring will be tall?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
Correct Answer: C) 50%
Rationale: This is a monohybrid cross. The heterozygous parent (Tt) can produce two types of
gametes: T and t. The homozygous recessive parent (tt) can only produce one type of gamete: t.
A Punnett square of this cross (Tt x tt) shows that 50% of the offspring will have the genotype Tt
(tall phenotype) and 50% will have the genotype tt (short phenotype).
Question 2
Mendel's Law of Segregation states that:
A) Alleles for different traits are passed to offspring independently of one another.
B) During gamete formation, the two alleles for a trait separate from each other, so that each
gamete receives only one allele.
C) One allele in a pair may mask the effect of the other allele.
D) Offspring will always exhibit a blend of the parents' traits.
E) Dominant alleles are always more common in a population than recessive alleles.
Correct Answer: B) During gamete formation, the two alleles for a trait separate from each
other, so that each gamete receives only one allele.
Rationale: The Law of Segregation describes what happens to the alleles for a single gene. It
explains that the two alleles an individual possesses for a trait are separated (segregated) during
meiosis, ensuring that each gamete (sperm or egg) carries only one of the two alleles.
,[Type here]
Question 3
A cross between two individuals that are heterozygous for two different traits (e.g., RrYy x
RrYy) is expected to produce what phenotypic ratio in the offspring, assuming independent
assortment?
A) 1:1
B) 3:1
C) 1:2:1
D) 9:3:3:1
E) 1:1:1:1
Correct Answer: D) 9:3:3:1
Rationale: This is the classic Mendelian dihybrid cross ratio. When two individuals
heterozygous for two independently assorting genes are crossed, the offspring phenotypes will
appear in a 9:3:3:1 ratio, representing the four possible combinations of dominant and recessive
traits.
Question 4
Red-green color blindness is an X-linked recessive trait. If a colorblind woman (XᶜXᶜ) has
children with a man who has normal vision (X⁺Y), what is the probability that their son will be
colorblind?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
Correct Answer: E) 100%
Rationale: A son inherits his Y chromosome from his father and one of his mother's X
chromosomes. Since the mother is colorblind, both of her X chromosomes carry the recessive
allele (Xᶜ). Therefore, any son she has must inherit one of her Xᶜ chromosomes and will be
colorblind (XᶜY).
, [Type here]
Question 5
In snapdragons, flower color is an example of incomplete dominance. A cross between a red-
flowered plant (CᴿCᴿ) and a white-flowered plant (CᵂCᵂ) produces pink-flowered offspring
(CᴿCᵂ). What is the expected phenotypic ratio if two pink-flowered plants are crossed?
A) 3 red : 1 white
B) 1 red : 2 pink : 1 white
C) 1 red : 1 white
D) All pink
E) 9 red : 3 pink : 1 white
Correct Answer: B) 1 red : 2 pink : 1 white
Rationale: The cross is CᴿCᵂ x CᴿCᵂ. The resulting genotypes will be in a 1:2:1 ratio: 1 CᴿCᴿ
(red), 2 CᴿCᵂ (pink), and 1 CᵂCᵂ (white). Because the heterozygous phenotype is distinct from
both homozygous phenotypes, the phenotypic ratio matches the genotypic ratio.
Question 6
The process of synthesizing an RNA molecule from a DNA template is called:
A) Translation
B) Replication
C) Transcription
D) Transformation
E) Transduction
Correct Answer: C) Transcription
Rationale: Transcription is the first step of gene expression, where the information stored in a
segment of DNA (a gene) is copied into a messenger RNA (mRNA) molecule by the enzyme
RNA polymerase.
