Two DNA molecule in a cell are observed but not distinct is these phases

Options

A. S and `G_(2)`
B. `G_(2)` prophase
C. Metaphase and anaphase
D. `G_(1) and G_(2)` phase

Answer

To solve the question regarding the observation of two DNA molecules in a cell that are not distinct, we need to analyze the different phases of the cell cycle and understand the characteristics of DNA during these phases.

### Step-by-Step Solution:

1. **Understanding the Cell Cycle Phases**:
- The cell cycle consists of several phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis).
- During these phases, the state of DNA varies significantly.

2. **Identifying the S Phase**:
- In the S phase, DNA replication occurs. Each chromosome is duplicated, resulting in two identical sister chromatids for each chromosome.
- At this stage, although there are two sets of DNA, they are not yet distinct because they are still in the form of chromatin and have not condensed into visible chromosomes.

3. **Examining the G2 Phase**:
- The G2 phase follows the S phase and is a period of preparation for mitosis. The DNA is still in the form of chromatin and has not yet condensed into distinct chromosomes.
- Therefore, in the G2 phase, the DNA is also not distinct.

4. **Analyzing Other Phases**:
- In the **Prophase**, chromosomes condense and become visible, making them distinct. Thus, this phase cannot be the answer.
- In the **Metaphase** and **Anaphase**, chromosomes are clearly visible and distinct, so these options are also incorrect.
- In the **G1 phase**, the DNA is already present in a distinct form, so this option is also incorrect.

5. **Conclusion**:
- The only phases where two DNA molecules can be observed but are not distinct are the S phase and the G2 phase. Therefore, the correct answer is **S and G2 phase**.

### Final Answer:
The correct answer is **S and G2 phase**.

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