Question

Cleavage starts in human zygote at

• A. Fallopian tube
• B. Uterus
• C. Vagina
• D. None of the above

Answer 1

Answer: (A)

Fallopian tube

Fertilization in the fallopian tube gives rise to zygote. The mitotic division, called as cleavage starts as the zygote moves through the isthmus of the oviduct towards the uterus and forms 2, 4, 8, 16 daughter cells, called as blastomeres. The embryo with 8 to 16 blastomeres is called as morula. The morula continues to divide and transforms into blastocyst as it moves further into the uterus. The blastomeres in the blastocyst are arranged into an outer layer is called as trophoblast and an inner group of cells attached to trophoblast called as the inner cell mass. The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo.

After attachment, the uterine cells divide rapidly and covers the blastocyst. As a result, the blastocyst becomes embedded in the endometrium of the uterus. This is called as implantation and it leads to pregnancy.

Thus, the correct option is (A).