149. Which stage of mitosis is blocked by colchicine?
1. Prophase
2. Telophase
3. Anaphase
4. Metaphase

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Introduction

Colchicine is a chemical compound commonly used in biological research and medicine. It plays a significant role in halting cell division by targeting a specific phase of mitosis. Understanding how colchicine affects mitosis helps in studying chromosome behavior and has applications in genetics and cancer research.

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How Colchicine Affects Mitosis

Colchicine disrupts the normal process of mitosis by binding to tubulin, the protein that makes up microtubules. Microtubules are essential for forming the mitotic spindle, which aligns and separates chromosomes during cell division.

Specific Stage Blocked: Metaphase

• Colchicine arrests cells at the metaphase stage of mitosis.

• During metaphase, chromosomes are aligned at the metaphase plate, and spindle fibers are attached to the centromeres.

• Colchicine prevents spindle fiber formation, thereby inhibiting chromosome separation, effectively freezing the cell in metaphase.

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Answer Explanation

Let’s review the options:

1. Prophase – Chromosomes condense, and spindle formation begins.
   ❌ Not blocked by colchicine directly.

2. Telophase – Chromosomes de-condense, and the nuclear envelope reforms.
   ❌ Occurs after chromosome separation.

3. Anaphase – Sister chromatids separate and move to opposite poles.
   ❌ Colchicine prevents this stage from occurring.

4. Metaphase – Chromosomes align; spindle fibers attach.
   ✅ Colchicine blocks spindle formation, arresting cells at this stage.

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Conclusion

Colchicine is a potent mitotic inhibitor that blocks mitosis at the metaphase stage by disrupting spindle fiber formation.

Correct Answer:
4. Metaphase