Germinal layer formed from trophoblast of mammalian blastocyst is

Options

A. Ectoderm
B. Endoderm
C. Mesoderm
D. None of the above.

Answer

To solve the question regarding the germinal layer formed from the trophoblast of the mammalian blastocyst, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Blastocyst Structure**:
- The mammalian blastocyst consists of two main parts: the outer layer called the trophoblast and the inner cell mass (ICM).

2. **Identifying the Role of Trophoblast**:
- The trophoblast is primarily responsible for the implantation of the blastocyst into the uterine wall and for providing nourishment to the developing embryo.

3. **Identifying the Role of Inner Cell Mass**:
- The inner cell mass (ICM) is the part of the blastocyst that will develop into the embryo itself. It is from this mass that the three germinal layers (ectoderm, mesoderm, and endoderm) are formed.

4. **Conclusion on Germinal Layers**:
- Since the trophoblast does not contribute to the formation of any germinal layer (ectoderm, mesoderm, or endoderm), the correct answer to the question is that no germinal layer is formed from the trophoblast.

5. **Final Answer**:
- Therefore, the correct option is **4. none of the above**.