ANATOMY

Detailed explanation-1: -The first cleavage in a frog’s egg is meridional i.e. from animal to vegetal pole resulting in a two-celled stage. These cells are also called blastomeres. The second cleavage is also meridional and results in four blastomeres. These all are of the same size.

Detailed explanation-2: -The first cleavage occurs shortly after the zygote nucleus forms. A furrow appears that runs longitudinally through the poles of the egg, passing through the point at which the sperm entered and bisecting the gray crescent. This divides the egg into two halves forming the 2-cell stage.

Detailed explanation-3: -The first cleavage plane is meridional which occurs at about 3-3½ hours after fertilization. But the time depends largely on extrinsic factors. The first cleavage starts at the animal pole and gradually travels towards the vegetal pole. Thus the egg is bisected along the poles.

Detailed explanation-4: -Because there is a moderate amount of yolk and unequal distribution of yolk present in the frog egg, the cleavage is of the holoblastic unequal type. This serves as a barrier during cell division.

Detailed explanation-5: -Around 24 hours after fertilization occurs, the first cleavage division occurs. The individual cells that are generated as a result of the cleavage are termed blastomeres and the cleavage phase ends when a hollow sphere of blastomeres called the blastula has formed.