Biology - Human Reproduction Question with Solution | TestHub
During early embryonic development in humans, which of the following options shows the correct sequence of the various events given below.
I. Formation of hypoblast and epiblast
II. Appearance of primitive streak
III. Differentiation of cytotrophoblast and syncytiotrophoblast.
IV. Formation of amnion
Options:
Answer:
Solution:
During early embryonic development, implantation starts around the 7th to 8th day. The trophoblast first differentiates into two layers: an inner cytotrophoblast and an outer syncytiotrophoblast (III).
Around the 8th day, the inner cell mass (embryoblast) differentiates into a bilaminar embryonic disc consisting of two layers: the hypoblast and the epiblast (I).
Following this, a small cavity appears within the epiblast, which enlarges to form the amniotic cavity. The epiblast cells adjacent to the cytotrophoblast differentiate into amnioblasts, which form the amnion (IV).
During the beginning of the third week of development (around day 14-15), gastrulation begins with the appearance of the primitive streak on the surface of the epiblast (II).
Thus, the correct sequence of events is III I IV II.
Answer: III I IV II
