The photomicrographs show cells in various stages of the cell cycle. Identify the stage where semi - conservative replication of DNA take place.

Options

A.
B.
C.
D.

Answer

To solve the question regarding the stage of the cell cycle where semi-conservative replication of DNA takes place, let's break it down step by step:

### Step 1: Understand the Cell Cycle
The cell cycle consists of several stages, including:
- Interphase (G1, S, G2 phases)
- Mitosis (Prophase, Metaphase, Anaphase, Telophase)

### Step 2: Identify the Stages of Interphase
Interphase is divided into three sub-phases:
- **G1 phase (Gap 1)**: Cell growth and preparation for DNA synthesis.
- **S phase (Synthesis)**: DNA replication occurs here.
- **G2 phase (Gap 2)**: Further growth and preparation for mitosis.

### Step 3: Focus on the S Phase
The question specifically asks for the stage where semi-conservative replication of DNA occurs. During the S phase, each DNA molecule is replicated, resulting in two identical DNA molecules, each consisting of one original strand and one newly synthesized strand. This is known as semi-conservative replication.

### Step 4: Analyze the Photomicrographs
The question mentions photomicrographs showing various stages of the cell cycle. While analyzing these images:
- **Metaphase**: Chromosomes are aligned at the equator, no DNA replication occurs.
- **Anaphase**: Chromatids are moving to opposite poles, no DNA replication occurs.
- **Prophase**: Chromosomes condense, no DNA replication occurs.
- **Interphase (S phase)**: This is where DNA replication occurs.

### Conclusion
The stage where semi-conservative replication of DNA takes place is the **S phase** of Interphase.

### Final Answer
**The S phase of Interphase is the stage where semi-conservative replication of DNA occurs.**

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