A mature mammalian erythrocyte characteristically has :

Options

A. a bilobed nucleus
B. no nucleus
C. numerous plastids
D. two centrioles

Explanation

To answer the question about the characteristics of a mature mammalian erythrocyte, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Erythrocytes**:
- Erythrocytes, commonly known as red blood cells (RBCs), are specialized cells in mammals that are primarily responsible for the transport of oxygen and carbon dioxide in the blood.

2. **Key Characteristics of Mature Mammalian Erythrocytes**:
- Unlike many other cells in the body, mature mammalian erythrocytes are unique in their structure and function.

3. **Nucleus Presence**:
- A defining feature of mature mammalian erythrocytes is that they **lack a nucleus**. This is significant because the absence of a nucleus allows for more space within the cell to accommodate hemoglobin, the protein that binds oxygen.

4. **Shape of Erythrocytes**:
- The lack of a nucleus contributes to the **biconcave disc shape** of RBCs. This shape increases the surface area for gas exchange and facilitates efficient diffusion of gases (oxygen and carbon dioxide).

5. **Comparison with Options**:
- Given the options:
- A. Bilobed nucleus
- B. No nucleus
- C. Numerous plastids
- D. Two centros
- The only correct option that accurately describes a mature mammalian erythrocyte is **B. No nucleus**.

6. **Conclusion**:
- Therefore, the characteristic feature of a mature mammalian erythrocyte is that it has **no nucleus**.

### Final Answer:
The correct answer is **B. No nucleus**.