Cleavage & Formation of Blastocyst - Practice Questions & MCQ

• The mitotic division starts as the zygote moves through the isthmus of the oviduct called cleavage towards the uterus and forms 2, 4, 8, 16 daughter cells called blastomeres. 
• When the blastomeres divide completely the cleavage is called holoblastic cleavage.
• The embryo with 8 to 16 blastomeres is called a morula.
• The embryo gradually becomes a 64-celled structure.
• A cavity is now formed within the cell mass. This cavity is called the blastocyst cavity or blastocoel.
• The embryo is now termed the blastocyst.
• The blastocyst is made up of an outer layer of cells called the trophoblast or trophectoderm and an inner cell mass or embryoblast.
• The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo.

Significance of Cleavage:

• Cleavage distributes the cytoplasm of the zygote amongst the blastomeres.
• It allows for morphogenetic movements necessary for cell differentiation, germ layer formation and tissue and organ formation.
• It converts the unicellular zygote into a multicellular embryo.