Question

An egg of a frog is divided in a way, that one part has animal hemisphere and another part is deficient, in that

• A. Only animal hemisphere region forms embryo.
• B. Both the sites form embryo.
• C. Embryo is not formed from any region.
• D. Animal hemisphere-deficient region forms the embryo.

Answer 1

The correct option is A Only animal hemisphere region forms embryo.

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 eggs of amphibians are moderately telolecithal (mesolecithal). Although cleavage is radial and holoblastic, the divisions in the vegetal hemisphere are slowed by the presence of the inert yolk. As a result, the blastula consists of many small cells in the animal hemisphere and fewer but larger cells in the vegetal hemisphere. The blastocoel is displaced toward the animal pole. The cells of animal hemisphere eventually form the embryo.