Analyze the events occurring during every stage of the cell cycle, how the amount of DNA content (C) per cell changes and select the correct option.

Options

A. DNA content becomes doubled during S phase of cell cycle
B. DNA content is reduced to half during anaphase
C. DNA content remain same during meiosis I
D. Both (a) and (b)

Answer

To analyze the events occurring during every stage of the cell cycle and how the amount of DNA content (C) per cell changes, we can break down the cell cycle into its main phases: Interphase (which includes G1, S, and G2 phases) and the Mitotic phase (M phase, which includes prophase, metaphase, anaphase, and telophase). Here’s a step-by-step explanation:

### Step 1: Understand the Cell Cycle Phases
- **Interphase**: This is the phase where the cell spends most of its time and is divided into three sub-phases:
- **G1 Phase (Gap 1)**: The cell grows and synthesizes proteins necessary for DNA replication. The DNA content is at 2C (where C represents the amount of DNA in a haploid cell).
- **S Phase (Synthesis)**: DNA replication occurs, and the amount of DNA content doubles. At the end of this phase, the DNA content is 4C.
- **G2 Phase (Gap 2)**: The cell continues to grow and prepares for mitosis. The DNA content remains at 4C.

### Step 2: Analyze the M Phase
- **M Phase (Mitosis)**: This phase is where the cell divides.
- **Prophase**: Chromatin condenses into chromosomes, and the DNA content is still 4C.
- **Metaphase**: Chromosomes align at the cell's equatorial plane, with the DNA content still at 4C.
- **Anaphase**: Sister chromatids are pulled apart to opposite poles of the cell. At this point, the DNA content effectively reduces to 2C per daughter cell as each chromatid is considered a separate chromosome.
- **Telophase**: The cell prepares to divide into two. The DNA content is still at 2C until the cell fully divides.

### Step 3: Summary of DNA Content Changes
- **G1 Phase**: 2C
- **S Phase**: 4C (DNA replication occurs)
- **G2 Phase**: 4C
- **M Phase**:
- Prophase: 4C
- Metaphase: 4C
- Anaphase: 2C (as chromatids separate)
- Telophase: 2C (before cytokinesis)

### Step 4: Evaluate the Options
1. **DNA content becomes doubled during the S phase**: **Correct** (DNA content goes from 2C to 4C).
2. **DNA content reduced to half during anaphase**: **Correct** (DNA content goes from 4C to 2C).
3. **DNA content remains the same during meiosis one**: **Incorrect** (DNA content does not remain the same; it reduces during anaphase of meiosis).

### Conclusion
The correct options are 1 and 2.

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