Q1. During the cell cycle, a specific phase is characterized by the replication of DNA and the duplication of centrosomes. If a cell fails to complete this phase accurately, it may lead to genetic instability. Which phase is being described?
A) G1 Phase
B) S Phase
C) G2 Phase
D) M Phase
Rationale:
Correct Answer (B): The S Phase (Synthesis Phase) is the specific period during Interphase where DNA replication occurs, ensuring each daughter cell receives a complete set of chromosomes.
Option A: G1 Phase is the "growth phase" where the cell increases in size and prepares proteins, but DNA is not yet replicated.
Option C: G2 Phase occurs after DNA replication; it is a period of further growth and final preparations for entry into mitosis.
Option D: M Phase (Mitotic Phase) is the actual process of nuclear and cytoplasmic division, not the replication of DNA.
Q2. In Meiosis I, a unique process occurs where homologous chromosomes pair up and exchange genetic material. This process is vital for genetic diversity in offspring. What is this process called, and in which sub-phase does it occur?
A) Cytokinesis in Telophase I
B) Segregation in Anaphase I
C) Crossing over in Prophase I
D) Independent assortment in Metaphase I
Rationale:
Correct Answer (C): Crossing over occurs during the Pachytene stage of Prophase I. It involves the exchange of genetic segments between non-sister chromatids, creating unique genetic combinations.
Option A: Cytokinesis is the physical division of the cytoplasm and occurs at the very end of the cell division process.
Option B: Segregation refers to the pulling apart of homologous chromosomes, which happens during Anaphase I, but it does not involve the exchange of material.
Option D: Independent assortment is the random alignment of chromosomes at the equator during Metaphase I, not the physical exchange of genes.
Q3. A nursing student is observing a cell under a microscope and notices that the sister chromatids have separated and are moving toward opposite poles of the cell. Which stage of Mitosis is being observed?
A) Prophase
B) Metaphase
C) Anaphase
D) Telophase
Rationale:
Correct Answer (C): Anaphase is defined by the splitting of the centromeres and the migration of sister chromatids (now individual chromosomes) toward opposite poles.
Option A: In Prophase, the chromatin condenses into visible chromosomes and the nuclear envelope begins to disappear.
Option B: In Metaphase, chromosomes align at the center (metaphase plate) of the cell.
Option D: In Telophase, chromosomes reach the poles, and new nuclear membranes begin to form around the two sets of DNA.
Q4. How does Meiosis II differ significantly from Mitosis, even though the physical movements of chromosomes appear similar?
A) Meiosis II results in diploid cells, while Mitosis results in haploid cells.
B) DNA replication occurs immediately before Meiosis II but not Mitosis.
C) Meiosis II separates sister chromatids of haploid cells, while Mitosis separates them in diploid cells.
D) Mitosis involves two rounds of division, whereas Meiosis II is only one.
Rationale:
Correct Answer (C): Meiosis II is essentially a mitotic division of haploid cells (half the chromosome count), whereas Mitosis occurs in diploid cells to maintain the full chromosome count for tissue growth/repair.
Option A: This is reversed; Mitosis results in diploid cells and Meiosis results in haploid gametes.
Option B: DNA replication (S phase) does not occur between Meiosis I and Meiosis II, which is why the resulting cells are haploid.
Option D: This is incorrect. Mitosis is a single division, while the entire process of Meiosis involves two divisions (I and II).
Q5. A failure in the "Spindle Assembly Checkpoint" during Metaphase can lead to a condition where a daughter cell has an abnormal number of chromosomes (e.g., Trisomy). What is the medical term for this failure of chromosomes to separate properly?
A) Non-disjunction
B) Binary Fission
C) Apoptosis
D) Crossing Over
Rationale:
Correct Answer (A): Non-disjunction occurs when chromosomes or sister chromatids fail to separate during Anaphase. This results in one daughter cell having too many chromosomes and the other having too few (Aneuploidy).
Option B: Binary Fission is the simple method of asexual reproduction used by prokaryotes (bacteria), not complex eukaryotic cells.
Option C: Apoptosis is programmed cell death, which is a protective mechanism to remove damaged cells, not a division error.
Option D: Crossing over is a normal, healthy exchange of genetic material and does not refer to the failure of separation.
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