Question

If the amount of yolk and its distribution are changed in the egg. Which one is affected?

• A. Pattern of cleavage
• B. Formation of zygote
• C. Number of blastomeres
• D. Fertilisation

Answer 1

The correct option is A Pattern of cleavage

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.

Mammalian eggs have very little yolk, because the embryo obtains maternal nutritional support throughout most of its development; whereas the eggs of birds and reptiles must contain sufficient yolk to sustain the embryo until hatching.

Echinoderm eggs typically need only enough yolk to nourish the embryo until it becomes a tiny larva capable of obtaining its own food.

Pattern of cleavage depends on the yolk and its distribution in the egg.

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 as holoblastic cleavage. Many vertebrate eggs are telolecithal, meaning they have large amounts of yolk concentrated at one end of the cell, known as the vegetal pole. The opposite, more metabolically active, pole is the animal pole. The telolecithal eggs of reptiles and birds have very large amounts of yolk at the vegetal pole and only a small amount of cytoplasm concentrated at the animal pole.

Thus, the correct option is (A).