In man, nucleolar organisers are not located in which of the following chromosomes?

Options

A. 14
B. 20
C. 21
D. 13

Answer

To determine which chromosome in humans does not contain nucleolar organizers (NORs), we can follow these steps:

### Step 1: Understand Nucleolar Organizers (NORs)
Nucleolar organizers are specific chromosomal regions that are essential for the formation of the nucleolus. They are associated with the genes that code for ribosomal RNA (rRNA).

**Hint:** NORs are crucial for ribosome production in cells.

### Step 2: Identify Chromosomes with NORs in Humans
In humans, NORs are located on the short arms of acrocentric chromosomes. The specific chromosomes that contain NORs are:
- Chromosome 13
- Chromosome 14
- Chromosome 15
- Chromosome 21
- Chromosome 22

**Hint:** Focus on the acrocentric chromosomes when identifying NORs.

### Step 3: Analyze the Given Options
The question provides the following options:
- 14
- 20
- 21
- 13

From our previous step, we know that chromosomes 13, 14, and 21 have NORs.

**Hint:** Compare the options against the known list of chromosomes with NORs.

### Step 4: Identify the Chromosome Without NORs
The only chromosome from the options that does not belong to the list of chromosomes containing NORs is chromosome 20.

**Hint:** Look for the chromosome that is not part of the acrocentric group.

### Step 5: Conclusion
Therefore, the chromosome in humans that does not contain nucleolar organizers is chromosome 20.

**Final Answer:** Chromosome 20 (Option B) does not have nucleolar organizers.