At what stage of the cell cycle would you expect there to be twice the amount of DNA as normal?

Question

BlackTom AI · Accepted Answer

DNA is duplicated during S phase, so the DNA content per cell increases from the baseline (1×) to double (2×) by the time S phase finishes. After S phase the cell enters G2, during which it contains twice the normal DNA while it checks for replication errors and prepares for mitosis.

1) Relevant knowledge points and concepts
- Cell cycle phases: G1 (growth, unreplicated DNA), S (DNA synthesis/replication), G2 (post‑replication growth and checkpoint), M (mitosis/cell division).
- DNA content: before replication the cell has a single complement of DNA (call this 1×); after replication it has two complete sister chromatids per chromosome (2×) until mitosis segregates them into daughter nuclei.

2) Step‑by‑step reasoning
- At G1: DNA amount = 1× (normal, unreplicated).
- During S: replication is occurring; DNA amount is increasing from 1× toward 2× but is not fully doubled at the very beginning.
- At end of S and throughout G2: replication is complete, so DNA amount = 2×.
- During mitosis (after anaphase/cytokinesis): chromosomes segregate and each daughter cell returns to 1×.

3) Intermediate “calculation” steps (conceptual)
- Starting amount = 1×.
- After full replication in S: 1× + replicated copy = 2×.
- G2 contains the 2× amount until division reduces it back to 1× in each daughter cell.

4) Why the correct answer is correct
G2 follows S phase and is the period when all DNA has already been replicated, so the cell contains twice the usual amount of DNA while preparing for mitosis.

5) Why other choices are incorrect
- Beginning of S phase: replication has just started, so DNA is not yet fully doubled.
- During G1: DNA is unreplicated (1×).
- End of mitosis: daughter cells have completed division and return to the normal (1×) DNA content.
- "Never": incorrect because cells do have a doubled DNA amount transiently after S phase.

Conclusion: Therefore the stage with twice the amount of DNA is During G2, which matches the provided correct answer.

At what stage of the cell cycle would you expect there to be twice the amount of DNA as normal?Single choice

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