PCB 3063 Exam 1 V2 | PCB 3063 Genetics
| Actual Q&A with Rationale (PCB3063
Exam 1) | University of Central Florida
1. Which phase of the cell cycle involves the replication of genomic DNA to ensure each
daughter cell receives a full set of chromosomes?
A. S phase
B. G1 phase
C. G2 phase
D. M phase
Answer: A
Rationale: The S phase, or synthesis phase, is the period during which DNA is replicated to
ensure each daughter cell gets a copy. This occurs between the two gap phases of
interphase. Without this step, the cell would not have enough genetic material to divide
into two viable cells.
2. In a monohybrid cross between two individuals heterozygous for a recessive allele (Aa x
Aa), what is the expected phenotypic ratio in the F2 generation?
A. 1:2:1
B. 3:1
C. 9:3:3:1
,D. 1:1
Answer: B
Rationale: The phenotypic ratio of a standard Mendelian monohybrid cross is 3 dominant
to 1 recessive. This ratio results from the segregation of alleles into gametes and their
subsequent random combination. The genotypic ratio would be 1:2:1, but the dominant
phenotype masks the recessive allele in heterozygotes.
3. Mendel’s Law of Segregation is physically explained by the movement of chromosomes
during which stage of meiosis?
A. Anaphase I
B. Prophase I
C. Metaphase II
D. Telophase II
Answer: A
Rationale: The Law of Segregation states that two alleles for a trait separate during gamete
formation. This occurs during Anaphase I when homologous chromosomes are pulled to
opposite poles of the cell. This physical separation ensures each gamete receives only one
allele per locus.
4. What is the expected phenotypic ratio of a dihybrid cross (AaBb x AaBb) assuming
independent assortment and complete dominance?
A. 3:1
, B. 9:3:3:1
C. 1:1:1:1
D. 9:7
Answer: B
Rationale: The 9:3:3:1 ratio is the classic Mendelian result for two genes that assort
independently. It represents the probability of combining two 3:1 ratios (3/4 dominant,
1/4 recessive) for two different traits. Each phenotypic category represents a unique
combination of dominant and recessive expressions.
5. Which scientist(s) used radioactive phosphorus and sulfur to prove that DNA, not protein,
is the genetic material in bacteriophages?
A. Griffith
B. Avery, MacLeod, and McCarty
C. Watson and Crick
D. Hershey and Chase
Answer: D
Rationale: The Hershey-Chase experiment used P-32 to label DNA and S-35 to label
proteins in viruses. They observed that only the radioactive phosphorus entered the
bacterial cells during infection. This definitive experiment confirmed that DNA carries the
information needed for viral replication.
| Actual Q&A with Rationale (PCB3063
Exam 1) | University of Central Florida
1. Which phase of the cell cycle involves the replication of genomic DNA to ensure each
daughter cell receives a full set of chromosomes?
A. S phase
B. G1 phase
C. G2 phase
D. M phase
Answer: A
Rationale: The S phase, or synthesis phase, is the period during which DNA is replicated to
ensure each daughter cell gets a copy. This occurs between the two gap phases of
interphase. Without this step, the cell would not have enough genetic material to divide
into two viable cells.
2. In a monohybrid cross between two individuals heterozygous for a recessive allele (Aa x
Aa), what is the expected phenotypic ratio in the F2 generation?
A. 1:2:1
B. 3:1
C. 9:3:3:1
,D. 1:1
Answer: B
Rationale: The phenotypic ratio of a standard Mendelian monohybrid cross is 3 dominant
to 1 recessive. This ratio results from the segregation of alleles into gametes and their
subsequent random combination. The genotypic ratio would be 1:2:1, but the dominant
phenotype masks the recessive allele in heterozygotes.
3. Mendel’s Law of Segregation is physically explained by the movement of chromosomes
during which stage of meiosis?
A. Anaphase I
B. Prophase I
C. Metaphase II
D. Telophase II
Answer: A
Rationale: The Law of Segregation states that two alleles for a trait separate during gamete
formation. This occurs during Anaphase I when homologous chromosomes are pulled to
opposite poles of the cell. This physical separation ensures each gamete receives only one
allele per locus.
4. What is the expected phenotypic ratio of a dihybrid cross (AaBb x AaBb) assuming
independent assortment and complete dominance?
A. 3:1
, B. 9:3:3:1
C. 1:1:1:1
D. 9:7
Answer: B
Rationale: The 9:3:3:1 ratio is the classic Mendelian result for two genes that assort
independently. It represents the probability of combining two 3:1 ratios (3/4 dominant,
1/4 recessive) for two different traits. Each phenotypic category represents a unique
combination of dominant and recessive expressions.
5. Which scientist(s) used radioactive phosphorus and sulfur to prove that DNA, not protein,
is the genetic material in bacteriophages?
A. Griffith
B. Avery, MacLeod, and McCarty
C. Watson and Crick
D. Hershey and Chase
Answer: D
Rationale: The Hershey-Chase experiment used P-32 to label DNA and S-35 to label
proteins in viruses. They observed that only the radioactive phosphorus entered the
bacterial cells during infection. This definitive experiment confirmed that DNA carries the
information needed for viral replication.
