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Assertion : Holoblastic cleavage with almost equal-sized blastomeres is a characteristic of placental animals.

Reason : Eggs of most mammals, including humans, are of centrolecithal type

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is not correct explanation of A

(c) A is true but R is false

(d) A and R are false

1 Answer

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Best answer

Correct option (c) A is true but R is false

Explanation :

In holoblastoc cleavage, the cleavage furrows bisect the entire egg, or in other words, entire egg divides by each cleavage furrow. In placental mammals having isolecithal or mirolecithal egg, the holoblastic cleavage produces blastomeres of equal or approximately equal size. 

Centrolecithal eggs are found in insects and in some hydrozoa. Here, yolk is concentrated at the centre of egg and the cytoplasm is present surrounding it. Meroblastic cleavage occurs in them.

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