It is important that the centromere does not divide until the end of metaphase because it
(a) contains the genes that control prophase
(b) holds the replicated DNA molecules together
(c) is connected to the nuclear membrane
(d) produces the spindle fibres

Options

A. contains the genes that control prophase
B. holds the replicated DNA molecules together
C. is connected to the nuclear membrane
D. produces the spindle fibres

Answer

To solve the question regarding the importance of the centromere not dividing until the end of metaphase, we can analyze each option provided:

1. **Understanding the Centromere**: The centromere is the region of a chromosome where the two sister chromatids are joined together. It plays a crucial role during cell division, particularly in ensuring that the chromatids are properly separated into daughter cells.

2. **Analyzing the Options**:
- **Option (a)**: "Contains the genes that control prophase." This is incorrect because the centromere does not contain genes that control prophase; rather, it is involved in the attachment of spindle fibers during metaphase.
- **Option (b)**: "Holds the replicated DNA molecules together." This option is correct. The centromere is essential for holding the sister chromatids together until they are ready to be separated during anaphase. If the centromere were to divide before metaphase is complete, the chromatids would separate prematurely, leading to unequal distribution of genetic material.
- **Option (c)**: "Is connected to the nuclear membrane." This is incorrect. The centromere is not directly connected to the nuclear membrane; it is involved in the attachment of spindle fibers during cell division.
- **Option (d)**: "Produces the spindle fibers." This is also incorrect. The spindle fibers are produced by the centrosomes, not the centromere.

3. **Conclusion**: The correct answer is **(b)** "holds the replicated DNA molecules together." This is because the centromere's primary function is to ensure that the sister chromatids remain attached until the appropriate stage of cell division, which is crucial for the accurate distribution of genetic material.

### Step-by-Step Solution:
1. Identify the role of the centromere in cell division.
2. Evaluate each option provided in the question.
3. Determine which option correctly describes the function of the centromere during metaphase.
4. Conclude that the correct answer is (b) "holds the replicated DNA molecules together."