Which one of the following statements is correct?

Options

A. Cell divided by cytokinesis only in mitosis
B. DNA is replicated before the start of meiosis only
C. Spindles consisting of microtubules are formed only in mitosis
D. Exchange of genetic materials occurs only in meiosis

Answer

To determine which statement is correct, let's analyze each option step by step:

### Step 1: Analyze Option 1
**Statement:** "Cell divides by cytokinesis only in mitosis."
- **Explanation:** Cytokinesis is the process of cytoplasmic division that occurs after mitosis and meiosis. Therefore, this statement is incorrect because cytokinesis occurs in both mitosis and meiosis.

### Step 2: Analyze Option 2
**Statement:** "DNA is replicated before the start of meiosis only."
- **Explanation:** DNA replication occurs during the S phase of the cell cycle, which happens before both mitosis and meiosis. Hence, this statement is also incorrect.

### Step 3: Analyze Option 3
**Statement:** "Spindles consisting of microtubules are formed only in mitosis."
- **Explanation:** Spindle fibers, which are made of microtubules, are essential for the separation of chromosomes and are formed during both mitosis and meiosis. Thus, this statement is incorrect.

### Step 4: Analyze Option 4
**Statement:** "Exchange of genetic material occurs only in meiosis."
- **Explanation:** The exchange of genetic material, known as recombination or crossing over, occurs during meiosis but does not occur in mitosis. Therefore, this statement is correct.

### Conclusion
The correct answer is **Option 4: "Exchange of genetic material occurs only in meiosis."**

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