Which event results in gain or loss of chromosomes during cell division cycle?

Options

A. Seggregation of chromosomes at Meta phase.
B. Seggregation of chromosomes at Anaphase.
C. Seggregation of chromosomes at Telo phase.
D. Both (a) and (c)

Explanation

To answer the question regarding which event results in the gain or loss of chromosomes during the cell division cycle, we need to analyze the options provided and understand the processes involved in cell division, specifically during mitosis and meiosis.

### Step-by-Step Solution:

1. **Understanding Chromosome Segregation**:
- During cell division, chromosomes must be accurately segregated to ensure that each daughter cell receives the correct number of chromosomes. This process is crucial for maintaining genetic stability.

2. **Identifying Key Phases of Cell Division**:
- The main phases of cell division where chromosome segregation occurs are:
- **Metaphase**: Chromosomes align at the cell's equatorial plane.
- **Anaphase**: Chromatids (or homologous chromosomes in meiosis) are pulled apart to opposite poles of the cell.
- **Telophase**: Chromosomes begin to de-condense, and the nuclear envelope re-forms around each set of chromosomes.

3. **Analyzing the Options**:
- **Option A: Segregation of chromosomes at metaphase**: This phase is primarily about alignment, not segregation.
- **Option B: Segregation of chromosomes at anaphase**: This is the correct phase where chromosomes are actually separated and pulled to opposite ends of the cell, leading to potential gain or loss of chromosomes if errors occur.
- **Option C: Segregation of chromosomes at telophase**: This phase involves the reformation of the nuclear envelope and does not involve the actual segregation of chromosomes.
- **Option D: Both A and C**: Since neither A nor C involves actual segregation, this option is incorrect.

4. **Conclusion**:
- The correct answer is **Option B: Segregation of chromosomes at anaphase**. This is the critical step where gain or loss of chromosomes can occur, particularly if there are errors in the separation process.