Use the figure to answer the question below.

In the figure, why does the amount of DNA in nucleus decrease from IV to V?

Question

Use the figure to answer the question below.

In the figure, why does the amount of DNA in nucleus decrease from IV to V?

BlackTom AI · Accepted Answer

To begin analyzing the figure, observe how the labeled regions change in DNA content across the stages shown.
Option 1: 'cells have lost chromosomes' — This is not accurate for a standard cell cycle diagram; lost chromosomes would imply an abnormal event like a chromosome loss, which is not what is depicted here. The chart shows normal progression, not chromosomal loss.
Option 2: 'cells have gone through mitosis and cytokinesis' — This is the plausible explanation. After mitosis and cytokinesis, the original nucleus partitions its DNA into two daughter cells, so the DNA content in a single nucleus decreases as the cell completes division. In the diagram, the drop from IV to V aligns with the completion of cytokinesis in the second cycle, resulting in reduced DNA content per nucleus.
Option 3: 'cells are in S phase' — During S phase, DNA is replicated, so the amount of DNA in the nucleus increases, not decreases. The graph would show an upward slope or plateau, not a drop, if the cells were in S phase.
Option 4: 'cells are in G2 phase' — G2 occurs after DNA replication but before mitosis; the DNA content remains the same as after S phase. A decrease at IV to V would not be expected in G2, so this choice contradicts the typical DNA-content pattern of the cell cycle.
In summary, the only option that appropriately explains a reduction in nuclear DNA content between those stages is that the cells have undergone mitosis and cytokinesis, which physically partitions and reduces DNA content per nucleus.

Use the figure to answer the question below. In the figure, why does the amount of DNA in nucleus decrease from IV to V?单项选择题

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