How many chromosomes will the cell have at G1 , after S , the after M - phase respectively , if it has 21 chromosomes at interphone ?

Options

A. 22,22,11
B. 22,22,22
C. 11,11,11
D. 11,22,22

Answer

To solve the question regarding the number of chromosomes in a cell at different phases of the cell cycle, we will follow these steps:

### Step-by-Step Solution:

1. **Identify the Initial Chromosome Count**:
- We are given that the cell has **21 chromosomes at interphase**. However, the video transcript mentions a correction that the actual count should be **22 chromosomes**. Therefore, we will consider **22 chromosomes** as the starting point.

2. **Determine the Chromosome Count in G1 Phase**:
- During the **G1 phase**, the cell is preparing for DNA replication but does not replicate its DNA yet. Hence, the number of chromosomes remains the same as in interphase.
- **Chromosome count in G1 = 22 chromosomes**.

3. **Determine the Chromosome Count after S Phase**:
- The **S phase** is when DNA replication occurs. Although the amount of DNA doubles, the number of chromosomes remains the same because each chromosome has been duplicated but still counts as one chromosome until mitosis occurs.
- **Chromosome count after S phase = 22 chromosomes**.

4. **Determine the Chromosome Count after M Phase**:
- The **M phase** (mitotic phase) involves the separation of the duplicated chromosomes into two daughter cells. However, the total number of chromosomes remains unchanged after mitosis.
- **Chromosome count after M phase = 22 chromosomes**.

### Final Summary:
- **Chromosome count in G1 phase = 22**
- **Chromosome count after S phase = 22**
- **Chromosome count after M phase = 22**

### Answer:
The cell will have **22 chromosomes at G1, 22 after S, and 22 after M phase** respectively.

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