Ohio State Molecular Genetics 4500 General Genetics
Exam Pack 2027 – Mendelian Genetics and Gene
Expression Problems
ABSTRACT
This comprehensive question bank has been developed for students preparing for the
Molecular Genetics 4500 (General Genetics) Final Examination at The Ohio State
University during the 2027 academic year. Molecular Genetics 4500 is a 3-credit course
covering the principles of genetics, including molecular genetics, transmission genetics
of prokaryotes and eukaryotes, developmental and non-chromosomal genetics,
recombinant DNA and genomics, and the genetics and evolution of populations. The
200 multiple-choice questions are organized into six major content areas aligned with
the official course syllabus: Mendelian Genetics & Inheritance Patterns (35 questions),
Chromosomal Basis of Inheritance & Sex Determination (35 questions), Gene Expression
& Regulation (35 questions), Mutation & DNA Repair (30 questions), Population
Genetics & Hardy-Weinberg Equilibrium (35 questions), and Developmental Genetics &
Quantitative Traits (30 questions). Each question includes a detailed Rationale
emphasizing problem-solving approaches, mathematical calculations, and conceptual
understanding essential for genetics analysis.
SECTION A: MENDELIAN GENETICS & INHERITANCE PATTERNS
(Questions 1-35)
1. In a monohybrid cross between two heterozygous organisms (Aa × Aa), what is
the expected phenotypic ratio?
A) 1:1
B) 3:1
C) 1:2:1
D) 9:3:3:1
,Answer: B
Rationale: A monohybrid cross between two heterozygotes (Aa × Aa) produces a 3:1
phenotypic ratio (3 dominant:1 recessive) and a 1:2:1 genotypic ratio (1 AA:2 Aa:1 aa).
2. A plant with round seeds (Ww) was crossed with a plant with wrinkled seeds
(ww). What are the expected phenotypic proportions of the offspring?
A) 100% round
B) 100% wrinkled
C) 50% round, 50% wrinkled
D) 75% round, 25% wrinkled
Answer: C
Rationale: This is a test cross (Ww × ww). The offspring will be 1 Ww (round): 1 ww
(wrinkled), giving a 1:1 phenotypic ratio. Based on the problem in the study materials,
220 round and 180 wrinkled offspring were observed, which is approximately 1:1.
3. In snapdragons, the allele for red flowers is incompletely dominant over the
allele for white flowers, producing pink heterozygotes. What is the expected
outcome of a cross between a red-flowered plant and a white-flowered plant?
A) 100% red
B) 100% pink
C) 50% red, 50% white
D) 25% red, 50% pink, 25% white
Answer: B
Rationale: In incomplete dominance, the heterozygote shows an intermediate
phenotype. Red (RR) × White (rr) produces all Rr offspring, which are pink.
4. In the same snapdragon system, what ratio would result from a cross between
two pink-flowered plants?
,A) 100% pink
B) 50% pink, 50% red
C) 25% red, 50% pink, 25% white
D) 50% pink, 50% white
Answer: C
Rationale: Pink (Rr) × Pink (Rr) produces 1 RR (red): 2 Rr (pink): 1 rr (white), which is a
1:2:1 ratio. This demonstrates that incomplete dominance produces distinct phenotypic
classes corresponding to genotypes.
5. What is the key difference between incomplete dominance and codominance?
A) In incomplete dominance, both alleles are expressed simultaneously; in codominance,
the phenotype is intermediate
B) In incomplete dominance, the phenotype is intermediate; in codominance, both
alleles are expressed simultaneously
C) There is no difference between the two
D) Incomplete dominance only occurs in plants; codominance only occurs in animals
Answer: B
Rationale: In incomplete dominance, the heterozygote shows a blended or
intermediate phenotype (e.g., pink flowers). In codominance, both alleles are fully
expressed in the heterozygote (e.g., AB blood type where both A and B antigens are
present).
6. A man with blood type AB has children with a woman with blood type O. What
blood types can their children have?
A) A and B only
B) AB and O only
C) A, B, AB, and O
D) Only O
Answer: A
Rationale: The man has genotype IAIB, and the woman has genotype ii. Their children
, can inherit either IA or IB from the father and i from the mother, resulting in blood types
A (IAi) or B (IBi).
7. The IA and IB alleles are codominant to each other, and both are dominant to
IO. In a population where the frequency of IA is 0.3, IB is 0.1, and IO is 0.6, what
percentage of the population would have blood type O?
A) 6%
B) 30%
C) 36%
D) 60%
Answer: C
Rationale: Blood type O occurs only in individuals with genotype IOIO. The frequency of
IOIO = (0.6)² = 0.36 or 36%.
8. In the same population, what percentage would have blood type AB?
A) 3%
B) 6%
C) 10%
D) 18%
Answer: B
Rationale: Blood type AB occurs in individuals with genotype IAIB. The frequency = 2 ×
(frequency of IA) × (frequency of IB) = 2 × 0.3 × 0.1 = 0.06 or 6%.
9. What is a test cross?
A) A cross between two heterozygous individuals
B) A cross between an individual with a dominant phenotype and a homozygous
recessive individual to determine genotype
Exam Pack 2027 – Mendelian Genetics and Gene
Expression Problems
ABSTRACT
This comprehensive question bank has been developed for students preparing for the
Molecular Genetics 4500 (General Genetics) Final Examination at The Ohio State
University during the 2027 academic year. Molecular Genetics 4500 is a 3-credit course
covering the principles of genetics, including molecular genetics, transmission genetics
of prokaryotes and eukaryotes, developmental and non-chromosomal genetics,
recombinant DNA and genomics, and the genetics and evolution of populations. The
200 multiple-choice questions are organized into six major content areas aligned with
the official course syllabus: Mendelian Genetics & Inheritance Patterns (35 questions),
Chromosomal Basis of Inheritance & Sex Determination (35 questions), Gene Expression
& Regulation (35 questions), Mutation & DNA Repair (30 questions), Population
Genetics & Hardy-Weinberg Equilibrium (35 questions), and Developmental Genetics &
Quantitative Traits (30 questions). Each question includes a detailed Rationale
emphasizing problem-solving approaches, mathematical calculations, and conceptual
understanding essential for genetics analysis.
SECTION A: MENDELIAN GENETICS & INHERITANCE PATTERNS
(Questions 1-35)
1. In a monohybrid cross between two heterozygous organisms (Aa × Aa), what is
the expected phenotypic ratio?
A) 1:1
B) 3:1
C) 1:2:1
D) 9:3:3:1
,Answer: B
Rationale: A monohybrid cross between two heterozygotes (Aa × Aa) produces a 3:1
phenotypic ratio (3 dominant:1 recessive) and a 1:2:1 genotypic ratio (1 AA:2 Aa:1 aa).
2. A plant with round seeds (Ww) was crossed with a plant with wrinkled seeds
(ww). What are the expected phenotypic proportions of the offspring?
A) 100% round
B) 100% wrinkled
C) 50% round, 50% wrinkled
D) 75% round, 25% wrinkled
Answer: C
Rationale: This is a test cross (Ww × ww). The offspring will be 1 Ww (round): 1 ww
(wrinkled), giving a 1:1 phenotypic ratio. Based on the problem in the study materials,
220 round and 180 wrinkled offspring were observed, which is approximately 1:1.
3. In snapdragons, the allele for red flowers is incompletely dominant over the
allele for white flowers, producing pink heterozygotes. What is the expected
outcome of a cross between a red-flowered plant and a white-flowered plant?
A) 100% red
B) 100% pink
C) 50% red, 50% white
D) 25% red, 50% pink, 25% white
Answer: B
Rationale: In incomplete dominance, the heterozygote shows an intermediate
phenotype. Red (RR) × White (rr) produces all Rr offspring, which are pink.
4. In the same snapdragon system, what ratio would result from a cross between
two pink-flowered plants?
,A) 100% pink
B) 50% pink, 50% red
C) 25% red, 50% pink, 25% white
D) 50% pink, 50% white
Answer: C
Rationale: Pink (Rr) × Pink (Rr) produces 1 RR (red): 2 Rr (pink): 1 rr (white), which is a
1:2:1 ratio. This demonstrates that incomplete dominance produces distinct phenotypic
classes corresponding to genotypes.
5. What is the key difference between incomplete dominance and codominance?
A) In incomplete dominance, both alleles are expressed simultaneously; in codominance,
the phenotype is intermediate
B) In incomplete dominance, the phenotype is intermediate; in codominance, both
alleles are expressed simultaneously
C) There is no difference between the two
D) Incomplete dominance only occurs in plants; codominance only occurs in animals
Answer: B
Rationale: In incomplete dominance, the heterozygote shows a blended or
intermediate phenotype (e.g., pink flowers). In codominance, both alleles are fully
expressed in the heterozygote (e.g., AB blood type where both A and B antigens are
present).
6. A man with blood type AB has children with a woman with blood type O. What
blood types can their children have?
A) A and B only
B) AB and O only
C) A, B, AB, and O
D) Only O
Answer: A
Rationale: The man has genotype IAIB, and the woman has genotype ii. Their children
, can inherit either IA or IB from the father and i from the mother, resulting in blood types
A (IAi) or B (IBi).
7. The IA and IB alleles are codominant to each other, and both are dominant to
IO. In a population where the frequency of IA is 0.3, IB is 0.1, and IO is 0.6, what
percentage of the population would have blood type O?
A) 6%
B) 30%
C) 36%
D) 60%
Answer: C
Rationale: Blood type O occurs only in individuals with genotype IOIO. The frequency of
IOIO = (0.6)² = 0.36 or 36%.
8. In the same population, what percentage would have blood type AB?
A) 3%
B) 6%
C) 10%
D) 18%
Answer: B
Rationale: Blood type AB occurs in individuals with genotype IAIB. The frequency = 2 ×
(frequency of IA) × (frequency of IB) = 2 × 0.3 × 0.1 = 0.06 or 6%.
9. What is a test cross?
A) A cross between two heterozygous individuals
B) A cross between an individual with a dominant phenotype and a homozygous
recessive individual to determine genotype
