GATE 2021 BT – Question 28

Plant, Animal and Microbial Biotechnology · Animals: Hybridoma technology, stem cells, animal cloning, transgenic, knock-out and knock-in animals · 1 mark · Multiple select

Which layers form from blastocyst inner cell mass?

Ectoderm
Endoderm
Mesoderm
Trophectoderm

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Correct answer: (A) Ectoderm; (B) Endoderm; (C) Mesoderm

Explanation

In the blastocyst there are two cell populations:

the **inner cell mass (ICM)**, which gives rise to the **embryo proper** (and the embryonic stem cells), and
the outer layer, the **trophectoderm**, which forms the placenta and extraembryonic tissues.

The ICM first forms the epiblast, which gives the three **germ layers** during gastrulation: **ectoderm, mesoderm and endoderm**. Trophectoderm does not come from the ICM.

Answer **A, B and C**.