For packing of a negatively charged DNA, a positively charged histone molecules rich in basic amino acids are required. This histones are formed during :

Options

A. `G_1` - phase
B. `G_2` - phase
C. S - phase
D. `G_0` - phase

Answer

To solve the question regarding when histone proteins are formed, we need to analyze the cell cycle and the role of histones in relation to DNA.

### Step-by-Step Solution:

1. **Understanding the Role of Histones**:
- Histones are positively charged proteins that are rich in basic amino acids, such as lysine and arginine. They play a crucial role in packaging DNA, which is negatively charged, into a compact structure within the nucleus.

2. **Cell Cycle Phases**:
- The cell cycle consists of two main phases: Interphase and M phase. Interphase is further divided into three sub-phases: G1, S, and G2.

3. **G1 Phase**:
- During the G1 phase, the cell is metabolically active, grows in size, and synthesizes various proteins. However, DNA replication does not occur in this phase.

4. **S Phase**:
- The S phase is specifically designated for DNA replication. During this phase, the DNA is duplicated, and since histones are required to package the newly synthesized DNA, histone proteins are also synthesized during this phase.

5. **G2 Phase**:
- In the G2 phase, the cell continues to grow and prepares for mitosis. While there is some protein synthesis, the primary focus of this phase is not on histone synthesis but rather on preparing the cell for division.

6. **Conclusion**:
- Since histones are synthesized during the S phase when DNA replication occurs, the correct answer to the question is **C, S phase**.

### Final Answer:
C, S phase