Given here are three statements about cell cycle.
I. Synthesis of histones and replication of DNA both occur during S-phase of inter phase.
II. After S-phase, each cell has double the number of chromosomes.
III. Separation of sister chromatids takes place during `G_2-` phase
Which of the given statements is/are true about cell cycle?

Options

A. Both II and II
B. Both I and I
C. Only II
D. Only I

Answer

To determine which statements about the cell cycle are true, we will analyze each statement one by one.

### Step 1: Analyze Statement I
**Statement I:** Synthesis of histones and replication of DNA both occur during S-phase of interphase.

- **Explanation:** The S-phase (Synthesis phase) of interphase is specifically the stage where DNA replication occurs. During this phase, histones are also synthesized to package the newly replicated DNA into chromatin. Therefore, this statement is **true**.

### Step 2: Analyze Statement II
**Statement II:** After S-phase, each cell has double the number of chromosomes.

- **Explanation:** After the S-phase, the DNA has been replicated, but the number of chromosomes does not double. Instead, each chromosome consists of two sister chromatids. The actual number of chromosomes remains the same until anaphase of mitosis, when the sister chromatids are separated. Therefore, this statement is **false**.

### Step 3: Analyze Statement III
**Statement III:** Separation of sister chromatids takes place during G2 phase.

- **Explanation:** The G2 phase is the period after DNA synthesis (S-phase) and before mitosis. The separation of sister chromatids occurs during the anaphase of mitosis, not during the G2 phase. Therefore, this statement is **false**.

### Conclusion
Based on the analysis:
- **Statement I is true.**
- **Statement II is false.**
- **Statement III is false.**

Thus, the only true statement about the cell cycle is Statement I.

### Final Answer:
**The correct answer is: Statement I only is true.**

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