Which of these pairs are incorrectly clubbed together?

Options

A. Cells in adult animals which do not divide - Heart cells
B. Equational division - Mitosis
C. Disc shaped structures at The surface of centromere - kinetochores
D. Initiation of assembly of mitotic spindle - Mitotic metaphase

Answer

To determine which of the pairs are incorrectly clubbed together, we need to analyze each option provided in the question.

### Step-by-Step Solution:

1. **Evaluate the First Pair**:
- The statement is about heart cells in adult animals not dividing.
- This is correct because cardiac muscle cells are terminally differentiated and do not undergo mitosis. They do not regenerate effectively after injury due to their complex structure.

2. **Evaluate the Second Pair**:
- The statement claims that mitosis is an equational division.
- This is also correct. In mitosis, the daughter cells maintain the same chromosome number as the parent cell (diploid to diploid).

3. **Evaluate the Third Pair**:
- The statement describes the kinetochore as a disc-shaped structure found on the surface of the centromere.
- This is accurate. The kinetochore is essential for the attachment of spindle fibers during cell division.

4. **Evaluate the Fourth Pair**:
- The statement claims that in mitotic metaphase, the initiation of mitotic spindle assembly occurs.
- This is incorrect. The assembly of the mitotic spindle actually begins in prophase, not metaphase. In metaphase, the spindle fibers are already formed and attached to the chromosomes, which are aligned at the metaphase plate.

### Conclusion:
The incorrectly matched pair is the fourth one, which states that the initiation of mitotic spindle assembly occurs in metaphase. The correct phase for this event is prophase.

### Final Answer:
The incorrectly clubbed pair is option D.

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