Subtopic: Fundamentals of Cell structure and signaling
Question Statement:
Which of the following layers) is/are formed from the inner cell mass of the
blastocyst?
Options:
(A) Ectoderm
(B) Endoderm
(C) Mesoderm
(D) Trophectoderm
Official Answer Key:
A,B,C
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2021 Q.28)**
**1. Governing Concept**:
- **Topic**: Developmental Biology & Embryonic Germ Layer Derivation
- During mammalian blastocyst development:
- The outer single-cell layer forms the **trophectoderm (trophoblast)**, which gives rise to extra-embryonic tissues including the embryonic portion of the placenta.
- The **inner cell mass (ICM)** gives rise to the entire embryo proper, segregating into epiblast and hypoblast, which subsequently gastrulate into the three primary germ layers:
1. **Ectoderm**: Gives rise to epidermis, nervous system, neural crest.
2. **Mesoderm**: Gives rise to muscle, bone, circulatory system, urogenital organs.
3. **Endoderm**: Gives rise to the epithelial lining of the gastrointestinal and respiratory tracts.
**2. Option Analysis**:
- **Option (A) [Ectoderm] is CORRECT**: Derived from the inner cell mass (epiblast lineage).
- **Option (B) [Endoderm] is CORRECT**: Derived from the inner cell mass.
- **Option (C) [Mesoderm] is CORRECT**: Formed by ingression of epiblast cells derived from the ICM during gastrulation.
- **Option (D) [Trophectoderm] is INCORRECT**: Originates from the outer blastocyst cell layer, not the inner cell mass.
**3. Final Answer**:
- **Correct Options**: **A, B, C**
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