Question

Pattern of cleavage in an egg of frog is
(A) Meroblastic
(B) Holoblastic unequal
(C) Holoblastic equal
(D) All the above

Answer 1

Hint: Reproduction is a biological process in which new individual organisms/ offspring are produced from their parents. They may be identical or can have a slight difference than their parents. There are many reproductive events in reproduction such as gametogenesis, insemination, fertilization, cleavage division in egg, implantation, gestation, parturition. Different organisms have different reproductive events. Their pattern of cleavage in egg also differs.

Complete answer:
(A) Meroblastic: It is a type of cleavage that occurs in very yolky eggs. In this process, the egg cytoplasm divides incompletely but not the yolk. It is a partial cleavage.
It is of two types: (a) Discoidal: This type of cleavage does not penetrate the yolk. The embryo forms a disc of cells.
 (b) Superficial: In this cleavage, cytokinesis does not take place and leads to a polynuclear egg.
Example: cephalopod molluscs (octopi, squid etc.)
(B) Holoblastic unequal: It is the cleavage which produces unequal size of blastomeres.
Example: frog egg, which contains a fair amount of yolk towards the vegetal pole. Because of the concentration of the yolk at the vegetal pole, the blastomeres formed in a different size.
(C) Holoblastic equal: It is the cleavage in which the blastomeres produced are of equal size.
Example: It occurs in Amphioxus egg where there is a little amount of yolk.

So, (B) is the correct option.

Additional information: Depending on the amount of yolk in the egg, the cleavage can be holoblastic or meroblastic. But holoblastic cleavage contains a commonly moderate or small amount of yolk in an egg.

Note:
 In the above, we detailed the cleavage division in an egg of different organisms. It is the stage where an embryo is formed. It described the different stages occurring during the division and the cells which divide are called blastomeres. After this stage implantation occurs and so on next events occur.