Answer-(b) Cleavage in human zygote is Unequal holoblastic. Cleavage occurs in the fallopian tube (oviduct) during the conduction of zygote towards uterus. It is holoblastic (because of microlecithal condition of egg), radial, indeterminate and unequal. First cleavage

Introduction:

Cleavage is the process of cell division that occurs immediately after fertilization of the egg, resulting in the formation of a multicellular organism. In humans, cleavage begins shortly after the zygote is formed and continues until the blastocyst stage.

Types of Cleavage:

There are two main types of cleavage: holoblastic and meroblastic.

Holoblastic Cleavage:

Holoblastic cleavage is a type of cell division that occurs throughout the entire zygote. It can further be classified into two subtypes: equal and unequal.

Holoblastic Equal Cleavage:

Holoblastic equal cleavage is characterized by the division of the zygote into daughter cells that are of equal size. This type of cleavage is observed in organisms with a small amount of yolk, as the evenly distributed yolk does not affect the division process. For example, in organisms like sea urchins and frogs, the zygote undergoes holoblastic equal cleavage.

Holoblastic Unequal Cleavage:

Holoblastic unequal cleavage is characterized by the division of the zygote into daughter cells that are of unequal size. This type of cleavage is observed in organisms with a moderate amount of yolk, as the yolk is not evenly distributed and affects the division process. For example, in organisms like birds and reptiles, the zygote undergoes holoblastic unequal cleavage.

Meroblastic Cleavage:

Meroblastic cleavage is a type of incomplete cleavage that occurs in organisms with a large amount of yolk. The yolk is not evenly distributed throughout the zygote, and only a portion of the zygote undergoes cell division. The rest of the yolk remains relatively undivided. This type of cleavage is observed in organisms like birds and reptiles.

Conclusion:

In the case of human zygote cleavage, it is neither holoblastic nor meroblastic. Instead, it undergoes a unique type of cleavage called rotational cleavage. Rotational cleavage is a combination of both equal and unequal cleavage, resulting in a blastocyst with a hollow cavity called a blastocoel. This blastocyst implants into the uterine wall and further develops into an embryo.