Every chromosome essentially has a (A)____ on the sides of which disc shaped structures called (B)_____ are present.

Answer

To solve the question, we need to fill in the blanks with the correct terms related to the structure of a chromosome.

1. **Understanding the Structure of a Chromosome**:
- A chromosome consists of two sister chromatids joined at a region called the centromere.

2. **Identifying the First Blank (A)**:
- The first blank asks what is present on the sides of the chromosome. The region where the two sister chromatids are joined is called the **centromere**. However, the question specifically refers to the structure that is present on the sides of the centromere, which is known as the **primary constriction**.

3. **Identifying the Second Blank (B)**:
- The second blank asks for the disk-shaped structures that are present on the sides of the primary constriction. These structures are known as **kinetochores**. Kinetochores are protein complexes that assemble on the centromere and are essential for the attachment of spindle fibers during cell division.

4. **Final Answer**:
- Therefore, the complete sentence would be: "Every chromosome essentially has a **primary constriction** on the sides of which disk-shaped structures called **kinetochores** are present."

### Summary of the Answers:
- (A) Primary constriction
- (B) Kinetochores