PCB 3063 Final Exam V3 | PCB 3063
Genetics | Actual Q&A with Rationale
(PCB3063 Final Exam) | University of
Central Florida
1. In a dihybrid cross between two individuals heterozygous for two independently assorting
traits (AaBb x AaBb), what is the expected phenotypic ratio?
A. 9:3:3:1
B. 3:1
C. 1:2:1
D. 1:1:1:1
Answer: A
Rationale: The 9:3:3:1 ratio is a classic Mendelian result for dihybrid crosses involving
independent assortment. This ratio represents the frequency of the four possible
phenotype combinations based on dominant and recessive traits. It assumes that there is
no linkage or epistasis between the two genes being studied.
2. Which enzyme is responsible for synthesizing the RNA primer during DNA replication?
A. Topoisomerase
B. DNA Polymerase III
C. Helicase
,D. DNA Primase
Answer: D
Rationale: DNA Primase is a specialized RNA polymerase that creates short RNA
sequences complementary to the DNA template. These primers provide the 3’-OH group
necessary for DNA Polymerase III to begin elongation. Without the activity of primase, DNA
replication cannot initiate on either the leading or lagging strands.
3. In the Hardy-Weinberg equation, what does the term ‘2pq’ represent?
A. Frequency of the dominant allele
B. Frequency of heterozygous individuals
C. Frequency of homozygous dominant individuals
D. Frequency of homozygous recessive individuals
Answer: B
Rationale: The term 2pq represents the frequency of heterozygotes in a population at
equilibrium. Here, p is the frequency of the dominant allele and q is the frequency of the
recessive allele. The sum of p squared, 2pq, and q squared must equal one for the
population to follow the model.
4. What type of mutation results in a premature stop codon in the mRNA sequence?
A. Missense mutation
B. Nonsense mutation
, C. Silent mutation
D. Frameshift mutation
Answer: B
Rationale: A nonsense mutation occurs when a single nucleotide change converts an
amino acid-specifying codon into a stop codon. This results in the truncated synthesis of
the polypeptide chain, often leading to a nonfunctional protein. It is distinct from missense
mutations, which merely swap one amino acid for another.
5. During which phase of Meiosis does crossing over occur between homologous
chromosomes?
A. Prophase I
B. Metaphase I
C. Anaphase II
D. Prophase II
Answer: A
Rationale: Crossing over occurs during the pachytene stage of Prophase I when
homologous chromosomes are paired in synapsis. This process involves the physical
exchange of genetic material between non-sister chromatids. It is a primary source of
genetic variation in sexually reproducing organisms.
Genetics | Actual Q&A with Rationale
(PCB3063 Final Exam) | University of
Central Florida
1. In a dihybrid cross between two individuals heterozygous for two independently assorting
traits (AaBb x AaBb), what is the expected phenotypic ratio?
A. 9:3:3:1
B. 3:1
C. 1:2:1
D. 1:1:1:1
Answer: A
Rationale: The 9:3:3:1 ratio is a classic Mendelian result for dihybrid crosses involving
independent assortment. This ratio represents the frequency of the four possible
phenotype combinations based on dominant and recessive traits. It assumes that there is
no linkage or epistasis between the two genes being studied.
2. Which enzyme is responsible for synthesizing the RNA primer during DNA replication?
A. Topoisomerase
B. DNA Polymerase III
C. Helicase
,D. DNA Primase
Answer: D
Rationale: DNA Primase is a specialized RNA polymerase that creates short RNA
sequences complementary to the DNA template. These primers provide the 3’-OH group
necessary for DNA Polymerase III to begin elongation. Without the activity of primase, DNA
replication cannot initiate on either the leading or lagging strands.
3. In the Hardy-Weinberg equation, what does the term ‘2pq’ represent?
A. Frequency of the dominant allele
B. Frequency of heterozygous individuals
C. Frequency of homozygous dominant individuals
D. Frequency of homozygous recessive individuals
Answer: B
Rationale: The term 2pq represents the frequency of heterozygotes in a population at
equilibrium. Here, p is the frequency of the dominant allele and q is the frequency of the
recessive allele. The sum of p squared, 2pq, and q squared must equal one for the
population to follow the model.
4. What type of mutation results in a premature stop codon in the mRNA sequence?
A. Missense mutation
B. Nonsense mutation
, C. Silent mutation
D. Frameshift mutation
Answer: B
Rationale: A nonsense mutation occurs when a single nucleotide change converts an
amino acid-specifying codon into a stop codon. This results in the truncated synthesis of
the polypeptide chain, often leading to a nonfunctional protein. It is distinct from missense
mutations, which merely swap one amino acid for another.
5. During which phase of Meiosis does crossing over occur between homologous
chromosomes?
A. Prophase I
B. Metaphase I
C. Anaphase II
D. Prophase II
Answer: A
Rationale: Crossing over occurs during the pachytene stage of Prophase I when
homologous chromosomes are paired in synapsis. This process involves the physical
exchange of genetic material between non-sister chromatids. It is a primary source of
genetic variation in sexually reproducing organisms.
