Question

Vitellogenesis is the process of
a. Formation of the vitelline membrane around the developing egg cell.
b. Formation of yolk sac membrane around the yolk mass during the development of reptiles and birds.
c. Formation of yolk and its deposition within the growing oocytes in amphibians.
d. None of the above.

Answer 1

Vitellogenesis is the process of deposited of nutrients in the female germ cell. This is involved in the reproduction of lecithotrophic organisms like reptiles, birds, and amphibians. It occurs in all groups of animals.

Complete answer:
- Vitellogenesis is the process of deposition of yolk.
- The yolk is chemically a lipoprotein, made up of phospholipids and neutral fats with a small amount of glycogen.
- It is synthesized in the liver of the female parent insoluble form.
- It is believed that mitochondria and Golgi complexes are responsible for converting the soluble form of the yolk into insoluble granules or platelets.

Yolk accumulation in animal embryology-
• Isolecithal is characterized by sparse and evenly distributed yolk.
• Mesolecthal is characterized by moderate and vegetal yolk disposition.
• Telolecithal is characterized by dense yolk that is present throughout the cell.
• Centrolecithal is characterized by the central placement of the yolk in the egg.

Amphibian vitellogenesis is a sex-limited protein found in the serum of normal females. The substance of egg yolk is derived from vitellogenesis. It is a protein that is synthesized by the liver and is induced by estrogen. The uptake of vitellogenin is stimulated by gonadotropins and is highly selective. Vitellogenin is converted within the yolk platelets as it is introduced to the oocyte.

Hence, the correct answer is option (C).

Note: In amphibians, the mesolecithal type yolk is present, and displaced radial cleavage occurs. The production and packaging of the nutrients, yolk proteins, into the developing oocyte in the ovary is important in providing the egg with the nutrient resource to complete the process of embryogenesis. This is known as vitellogenesis.