Question

When a zygote divides completely into blastomeres, the type of cleavage is called as

• A. Holoblastic
• B. Meroblastic
• C. Fertilization
• D. Metamorphosis

Answer 1

Answer: (A)

Holoblastic

Many animal eggs contain yolk, a mixture of proteins, phospholipids, and fats that serves as food for the developing embryo. The amount and distribution of yolk vary among different animal groups, depending on the needs of the embryo. Most invertebrates and simple chordates have isolecithal eggs with relatively small amounts of yolk uniformly distributed through the cytoplasm. Isolecithal eggs divide completely; this is called holoblastic cleavage. Cleavage of these eggs is radial or spiral. Radial cleavage is characteristic of deuterostomes, such as chordates and echinoderms; spiral cleavage is common in the embryos of protostomes, such as annelids and mollusks.

Meroblastic cleavage involves the partial cleavage of egg due to the presence of huge amount of yolk in them.

Thus, the correct option is (A).