The centromere or primary constriction of the chromosome contains rings of protein that are intimately associated with a spindle fibre. These rings are called :

Options

A. asters
B. secondary constrictions
C. centrioles
D. kinetochores

Answer

To solve the question regarding the rings of protein associated with the spindle fiber at the centromere of a chromosome, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of a Chromosome**:
- A chromosome consists of two sister chromatids joined at a region called the centromere, which is often referred to as the primary constriction.

2. **Identify the Role of the Centromere**:
- The centromere plays a crucial role during cell division, particularly during the metaphase stage of mitosis, where chromosomes align at the cell's equatorial plane.

3. **Recognize the Components Associated with the Centromere**:
- At the centromere, there are proteins that form structures that are essential for the attachment of spindle fibers. These spindle fibers are responsible for pulling the sister chromatids apart during cell division.

4. **Identify the Correct Terminology**:
- The specific rings of protein that are associated with the spindle fibers at the centromere are known as "kinetochores." These structures are critical for the movement of chromosomes during cell division.

5. **Choose the Correct Option**:
- Given the options: A) asters, B) secondary constrictions, C) centrioles, and D) kinetochores, the correct answer is D) kinetochores.

### Final Answer:
The rings of protein that are intimately associated with a spindle fiber at the centromere are called **kinetochores**.

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