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Q20. Briefly explain the embryonic development in humans.


Human embryonic development refers to the development and formation of the human embryo. It is characterised by the process of cell division and cellular differentiation of the embryo that occurs during the early stages of development.
Zygote divides rapidly by mitotic division as it moves through isthmus of oviduct towards uterus. This is
called cleavage.
As a result, 2, 4, 8, 16 daughter cells are produced which are termed as blastomeres.
Embryo with 8-16 blastomeres is called a morula. The morula continues to divide and transforms into a large mass of cells called blastocyst, which passes further into the uterus.
Blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called inner cell mass.
The trophoblast layer gets attached to the cells of the endometrium and the inner cell mass gives rise to the embryo.

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