BIO111 Exam 3 Actual Exam V3 | BIO111 General Biology (BIO111
Exam 3) | UCLA
1. Which phase of the cell cycle involves the replication of DNA?
A. G1 Phase
B. M Phase
C. G2 Phase
D. S Phase
Answer: D
Rationale: The S phase, or synthesis phase, is the specific period during interphase when
the cell replicates its genetic material. This process ensures that each daughter cell will
receive a complete set of chromosomes following division. DNA polymerase and other
enzymes are highly active during this stage to facilitate accurate copying.
2. In a heterozygous individual for a Mendelian trait, which allele is expressed in the
phenotype?
A. The dominant allele
B. Both alleles equally
C. The recessive allele
D. Neither allele
Answer: A
Rationale: According to the principle of dominance, the dominant allele will mask the
presence of a recessive allele in the phenotype. A heterozygous individual carries two
different alleles, but only the dominant one determines the observable characteristic. The
recessive trait only appears if the individual is homozygous for the recessive allele.
3. During which stage of meiosis does crossing over occur?
A. Metaphase I
B. Prophase I
C. Prophase II
D. Anaphase I
Answer: B
,Rationale: Crossing over is the exchange of genetic material between non-sister
chromatids of homologous chromosomes. This event occurs specifically during Prophase I
of meiosis when homologous pairs align closely in synapsis. It is a vital process for
increasing genetic variation among offspring.
4. Which enzyme is responsible for unwinding the DNA double helix during replication?
A. DNA Polymerase III
B. DNA Ligase
C. Primase
D. Helicase
Answer: D
Rationale: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases of the two DNA strands. This action creates a replication fork, allowing
other enzymes to access the template strands. Without helicase, the double helix would
remain tightly coiled and inaccessible for replication.
5. What is the flow of genetic information according to the Central Dogma of molecular
biology?
A. Protein to RNA to DNA
B. DNA to RNA to Protein
C. RNA to DNA to Protein
D. DNA to Protein to RNA
Answer: B
Rationale: The Central Dogma describes the directional transfer of genetic information
within a biological system. It begins with transcription, where DNA is used as a template to
synthesize mRNA. Subsequently, translation occurs, where the mRNA sequence is read by
ribosomes to build a specific protein.
6. A cross between two individuals heterozygous for a single trait (Aa x Aa) typically results in
what genotypic ratio?
A. 3:1
B. 1:2:1
C. 9:3:3:1
D. 1:1
Answer: B
, Rationale: A monohybrid cross between two heterozygotes results in three different
genotypes: AA, Aa, and aa. Statistically, the distribution is 25 percent homozygous
dominant, 50 percent heterozygous, and 25 percent homozygous recessive. This results in
the characteristic 1:2:1 genotypic ratio observed in Mendelian genetics.
7. Which molecule carries the anticodon and brings specific amino acids to the ribosome?
A. mRNA
B. tRNA
C. rRNA
D. snRNA
Answer: B
Rationale: Transfer RNA (tRNA) acts as the molecular adapter during protein synthesis. It
possesses a specific anticodon that base-pairs with a complementary codon on the mRNA
strand. Each tRNA molecule is covalently bonded to a specific amino acid, ensuring the
correct sequence in the polypeptide chain.
8. In humans, how many chromosomes are present in a gamete produced by meiosis?
A. 23
B. 46
C. 92
D. 44
Answer: A
Rationale: Meiosis is a reduction division process that halves the chromosome number of a
cell. While human somatic cells are diploid (2n=46), gametes like sperm and eggs are
haploid (n=23). This ensures that upon fertilization, the resulting zygote restores the
diploid number of 46.
9. What is the primary function of DNA Polymerase I?
A. Synthesizing the leading strand
B. Unwinding DNA
C. Connecting Okazaki fragments
D. Removing RNA primers and filling gaps
Answer: D
Rationale: DNA Polymerase I plays a critical role in the maturation of DNA strands during
replication. It identifies the RNA primers used to start synthesis and removes them using
Exam 3) | UCLA
1. Which phase of the cell cycle involves the replication of DNA?
A. G1 Phase
B. M Phase
C. G2 Phase
D. S Phase
Answer: D
Rationale: The S phase, or synthesis phase, is the specific period during interphase when
the cell replicates its genetic material. This process ensures that each daughter cell will
receive a complete set of chromosomes following division. DNA polymerase and other
enzymes are highly active during this stage to facilitate accurate copying.
2. In a heterozygous individual for a Mendelian trait, which allele is expressed in the
phenotype?
A. The dominant allele
B. Both alleles equally
C. The recessive allele
D. Neither allele
Answer: A
Rationale: According to the principle of dominance, the dominant allele will mask the
presence of a recessive allele in the phenotype. A heterozygous individual carries two
different alleles, but only the dominant one determines the observable characteristic. The
recessive trait only appears if the individual is homozygous for the recessive allele.
3. During which stage of meiosis does crossing over occur?
A. Metaphase I
B. Prophase I
C. Prophase II
D. Anaphase I
Answer: B
,Rationale: Crossing over is the exchange of genetic material between non-sister
chromatids of homologous chromosomes. This event occurs specifically during Prophase I
of meiosis when homologous pairs align closely in synapsis. It is a vital process for
increasing genetic variation among offspring.
4. Which enzyme is responsible for unwinding the DNA double helix during replication?
A. DNA Polymerase III
B. DNA Ligase
C. Primase
D. Helicase
Answer: D
Rationale: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases of the two DNA strands. This action creates a replication fork, allowing
other enzymes to access the template strands. Without helicase, the double helix would
remain tightly coiled and inaccessible for replication.
5. What is the flow of genetic information according to the Central Dogma of molecular
biology?
A. Protein to RNA to DNA
B. DNA to RNA to Protein
C. RNA to DNA to Protein
D. DNA to Protein to RNA
Answer: B
Rationale: The Central Dogma describes the directional transfer of genetic information
within a biological system. It begins with transcription, where DNA is used as a template to
synthesize mRNA. Subsequently, translation occurs, where the mRNA sequence is read by
ribosomes to build a specific protein.
6. A cross between two individuals heterozygous for a single trait (Aa x Aa) typically results in
what genotypic ratio?
A. 3:1
B. 1:2:1
C. 9:3:3:1
D. 1:1
Answer: B
, Rationale: A monohybrid cross between two heterozygotes results in three different
genotypes: AA, Aa, and aa. Statistically, the distribution is 25 percent homozygous
dominant, 50 percent heterozygous, and 25 percent homozygous recessive. This results in
the characteristic 1:2:1 genotypic ratio observed in Mendelian genetics.
7. Which molecule carries the anticodon and brings specific amino acids to the ribosome?
A. mRNA
B. tRNA
C. rRNA
D. snRNA
Answer: B
Rationale: Transfer RNA (tRNA) acts as the molecular adapter during protein synthesis. It
possesses a specific anticodon that base-pairs with a complementary codon on the mRNA
strand. Each tRNA molecule is covalently bonded to a specific amino acid, ensuring the
correct sequence in the polypeptide chain.
8. In humans, how many chromosomes are present in a gamete produced by meiosis?
A. 23
B. 46
C. 92
D. 44
Answer: A
Rationale: Meiosis is a reduction division process that halves the chromosome number of a
cell. While human somatic cells are diploid (2n=46), gametes like sperm and eggs are
haploid (n=23). This ensures that upon fertilization, the resulting zygote restores the
diploid number of 46.
9. What is the primary function of DNA Polymerase I?
A. Synthesizing the leading strand
B. Unwinding DNA
C. Connecting Okazaki fragments
D. Removing RNA primers and filling gaps
Answer: D
Rationale: DNA Polymerase I plays a critical role in the maturation of DNA strands during
replication. It identifies the RNA primers used to start synthesis and removes them using
