In humans, the mitotic division of the zygote (cleavage) starts as it…

The correct answer is Option (2) → Isthmus

Cleavage is the mitotic division of the zygote. Fertilisation takes place in the ampullary region of the oviduct, and the zygote then moves towards the uterus. The divisions start as it passes through the isthmus, the last narrow part of the oviduct that joins the uterus.

Option (1) Infundibulum — Incorrect. The infundibulum is the funnel-shaped part of the oviduct closest to the ovary. Its fimbriae collect the ovum after ovulation, before fertilisation has taken place.

Option (2) Isthmus — Correct. The zygote moves through the isthmus towards the uterus, and its mitotic division (cleavage) starts here, giving 2, 4, 8 and 16 blastomeres.

Option (3) Cervical canal — Incorrect. The cervical canal is the cavity of the cervix. With the vagina it forms the birth canal; the zygote never passes through it on its way to the uterus.

Option (4) Uterine cavity — Incorrect. By the time the embryo moves further into the uterus, cleavage is already going on and it has become a morula and then a blastocyst.

NCERT Extract:
Fertilisation and Implantation – “… The ovum released by the ovary is also transported to the ampullary region where fertilisation takes place.”
Fertilisation and Implantation – “… The mitotic division starts as the zygote moves through the isthmus of the oviduct called cleavage towards the uterus (Figure 2.11) and forms 2, 4, 8, 16 daughter cells called blastomeres. The embryo with 8 to 16 blastomeres is called a morula (Figure 2.11e). The morula continues to divide and transforms into blastocyst (Figure 2.11g) as it moves further into the uterus.”

Figure 2.11 Transport of ovum, fertilisation and passage of growing embryo through fallopian tube