Which checkpoint in the cell cycle ensures that DNA replication is complete and undamaged before proceeding to mitosis?
a) G1 checkpoint
b) S checkpoint
c) G2 checkpoint
d) M checkpoint
e) G0 checkpoint
Rationale: The G2 checkpoint ensures that DNA replication is complete and accurate, and any DNA damage is repaired before the cell enters mitosis. This checkpoint plays a crucial role in maintaining genomic stability and preventing the transmission of genetic errors to daughter cells.
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What is the role of cyclin-dependent kinases (CDKs) in regulating the cell cycle?
a) Initiating DNA replication
b) Repairing DNA damage
c) Regulating progression through cell cycle phases
d) Promoting cell differentiation
e) Inducing apoptosis
Rationale: Cyclin-dependent kinases (CDKs) are enzymes that regulate the cell cycle by phosphorylating target proteins involved in cell cycle progression. Their activity is tightly controlled by cyclins, which fluctuate in concentration throughout the cell cycle, ensuring orderly progression through each phase.
What is the consequence of a defect in the spindle checkpoint during mitosis?
a) Unequal distribution of chromosomes
b) Failure of cytokinesis
c) Premature entry into S phase
d) Arrest in G1 phase
e) Inability to replicate DNA
Rationale: The spindle checkpoint monitors the attachment of spindle fibers to kinetochores and ensures that chromosomes are properly aligned before proceeding to anaphase. A defect in this checkpoint can lead to unequal distribution of chromosomes, resulting in aneuploidy and genetic instability.
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Which phase of mitosis is characterized by the reformation of the nuclear envelope and decondensation of chromosomes?
a) Prophase
b) Metaphase
c) Anaphase
d) Telophase
e) Interphase
Rationale: Telophase marks the final stage of mitosis, during which the nuclear envelope reassembles around the separated chromosomes, and the chromatin decondenses. This process prepares the daughter cells for their respective functions in the interphase.
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What is the function of the mitotic spindle during mitosis?
a) Separating sister chromatids
b) Condensing chromosomes
c) Forming the nuclear envelope
d) Initiating DNA replication
e) Facilitating cytokinesis
Rationale: The mitotic spindle is responsible for separating sister chromatids and ensuring that each daughter cell receives an accurate and complete set of chromosomes. Its dynamic structure and motor proteins exert forces to move chromosomes to opposite poles during mitotic division.
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Which event occurs during telophase II of meiosis?
A) Separation of homologous chromosomes
B) Crossing over
C) Formation of haploid daughter cells
D) Alignment of chromosomes along the equatorial plate
E) Replication of DNA
Rationale: Telophase II is the final stage of meiosis, where the haploid daughter cells are formed as a result of the second round of cell division. Each daughter cell contains a unique combination of chromosomes, contributing to genetic diversity.
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What is the significance of independent assortment during meiosis?
A) It ensures the formation of diploid daughter cells
B) It leads to the production of identical offspring
C) It maintains the chromosome number in the daughter cells
D) It generates genetic variation among offspring
E) It occurs during prophase II
Rationale: Independent assortment is the random distribution of homologous chromosomes during meiosis, resulting in different combinations of alleles in the daughter cells. This process contributes to genetic diversity by producing gametes with various genetic compositions.
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Which of the following events occurs during prophase II of meiosis?
A) Synapsis of homologous chromosomes
B) Crossing over
C) Alignment of homologous chromosomes
D) Separation of sister chromatids
E) Formation of tetrads
Rationale: Prophase II is the phase of meiosis where the nuclear envelope breaks down, and spindle fibers attach to the sister chromatids. The subsequent separation of sister chromatids occurs during anaphase II, leading to the formation of haploid daughter cells.
How does meiosis contribute to genetic diversity?
A) By producing identical offspring
B) By maintaining the same chromosome number
C) By preventing crossing over
D) By allowing for random assortment of chromosomes
E) By only occurring in somatic cells
Rationale: Meiosis promotes genetic diversity through processes such as independent assortment, where homologous chromosomes align randomly during metaphase I, leading to different combinations of chromosomes in the daughter cells.
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Which of the following accurately describes a similarity between mitosis and meiosis?
A) Production of haploid daughter cells
B) Involvement of one round of cell division
C) Occurrence of crossing over
D) Maintenance of genetic diversity
E) Formation of gametes
Rationale: Both mitosis and meiosis involve the formation of daughter cells, although their purposes differ. While mitosis produces genetically identical diploid daughter cells for growth and repair, meiosis produces genetically diverse haploid gametes for sexual reproduction.