Question

Meroblastic cleavage is
A. Total
B. Spiral
C. Incomplete
D. Horizontal

Answer 1

Hint:Meroblastic cleavage is a form of cleavage that arises in very yolky eggs such as birds in which the egg cytoplasm and not the yolk divides.

Complete answer:
Cleavage is the division of cells in the developing embryo in developmental biology. The step is accompanied by fertilisation, with the transition initiated by the activation of the cyclin-dependent kinase complex. Depending on the amount of yolk in the shell, the cleavage can be holoblastic or meroblastic. The pole of the egg with the largest content of the yolk is referred to as the food pole, while the reverse is referred to as the animal pole. Cleavage differs from the other types of cell division by increasing the number of cells and the nuclear mass without changing the cytoplasmic mass. This means that for each subsequent subdivision, there is approximately half of the cytoplasm in each new cell than before the division, and thus the ratio of nuclear and cytoplasmic content increases.
Meroblastic cleavage arises in megalecithal or strongly telolecithal eggs with an immense volume of yolk. It is imperfect since it results in an imperfect isolation of blastomeres. The active part of the egg is limited to a small cytoplasmic area of the animal pole named the germinal disc or blastodisc. Cleavage furrows are limited to the germinal disc; the yolk is unclean. The first and second cleavage furrows are radially positioned at the right angles of the germinal disc and separated into four relatively equal but incomplete blastomeres. The remainder of the cleavage furrows is sporadic. Early blastomeres are incomplete and are continuous with the underlying yolk.

Thus, the correct answer is option C. i.e., Incomplete.

Note:There are two types of discoid and shallow meroblastic cleavage. Discoidal typically occurs in reptiles, birds, fish, etc. with telolecithal eggs and superficial cleavage in insects with centrolecithal eggs.