The position of secondary constriction is

Options

A. near centromere
B. at tip
C. constant
D. variable

Answer

To determine the position of secondary constriction on a chromosome, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Chromosome Structure**:
- Chromosomes have distinct regions, including the centromere, telomeres, and constrictions. The centromere is the central part of the chromosome where the two sister chromatids are joined.

**Hint**: Remember that the centromere is crucial for chromosome movement during cell division.

2. **Identifying the Centromere**:
- The first option mentions "near centromere." However, this is incorrect because the secondary constriction is not located near the centromere; instead, the centromere is associated with kinetochores.

**Hint**: Kinetochores are protein structures that form on the centromere and are important for chromosome segregation.

3. **Evaluating the Telomeres**:
- The second option states "at the tips." This is also incorrect because the tips of chromosomes are known as telomeres, which serve to protect the chromosome ends.

**Hint**: Telomeres prevent the chromosome from deterioration or fusion with neighboring chromosomes.

4. **Considering Constant Position**:
- The third option suggests "constant." This is not accurate either, as secondary constrictions can occur at various positions along the chromosome.

**Hint**: Think about how chromosomes can vary in structure, leading to different positions for secondary constrictions.

5. **Identifying the Correct Option**:
- The last option is "variable." This is the correct answer because secondary constrictions can occur at different locations on the chromosome, making their position variable.

**Hint**: Secondary constrictions can be found at different points on chromosomes, leading to variability.

### Conclusion:
The correct answer to the question about the position of secondary constriction is **variable** (option 4).