Describe the embryonic development of a zygote upto its implantation in humans.

. Zygote divides rapidly by mitotic division called cleavage and 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 changes 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.
. The cells of endometrium divide rapidly and cover the blastocyst. 
. So, the blastocyst gets embedded in the endometrium of the uterus called implantation leading to pregnancy.