In a cell, the number of chromosomes is the same, but the amount of DNA content has changed from C to 2C. Also, the amount of histones in the cell becomes double. In which stage of the cell cycle, this process could have happened?

Options

A. `G_(1)` phase
B. S phase
C. `G_(2)` phase
D. `G_(0)` phase

Answer

To solve the question regarding the stage of the cell cycle where the number of chromosomes remains the same but the DNA content changes from C to 2C, and the amount of histones doubles, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Chromosome and DNA Content**:
- In a cell, the term "C" refers to the amount of DNA in a haploid set of chromosomes. When the DNA content changes from C to 2C, it indicates that the DNA has been replicated.

2. **Identifying the Cell Cycle Phases**:
- The cell cycle consists of several phases: G1, S, G2, and M (mitosis).
- G1 phase is the first gap phase where the cell grows and prepares for DNA replication.
- S phase is the synthesis phase where DNA replication occurs.
- G2 phase is the second gap phase where the cell prepares for mitosis.
- G0 phase is a resting state where the cell is not actively preparing to divide.

3. **Analyzing the S Phase**:
- During the S phase, each chromosome is duplicated, resulting in two sister chromatids for each chromosome.
- Although the number of chromosomes remains the same, the total amount of DNA doubles from C to 2C.

4. **Histone Protein Synthesis**:
- Histones are proteins that help package DNA into a compact form. During the S phase, as DNA is replicated, the amount of histones also doubles to accommodate the newly synthesized DNA.

5. **Conclusion**:
- Since the question specifies that the number of chromosomes is unchanged while the DNA content doubles and histone content also doubles, the only phase where this occurs is the S phase.

### Final Answer:
The process described in the question occurs during the **S phase** of the cell cycle.