Question

Vitellogenesis occurs during the formation of
A) Primary oocyte in the graafian follicle
B) Oogonial cell in Graffian follicle
C) Ootid in the fallopian tube
D) Secondary oocyte in the fallopian tube

Answer 1

Vitellogenesis is also called yolk deposition. It is a process of production and accumulation of yolk in developing oocytes. Here we will explain vitellogenesis in detail and then will conclude the right answer for this question.

Complete answer:
Vitellogenesis:-
The term vitellogenesis comes from latin ‘vitellus’ which means egg yolk.Vitellogenesis is a process of yolk formation via nutrients and this yolk gets deposited in the oocyte or female germ cell. Chemically yolk is a lipoprotein that is composed of protein, phospholipids and fats with a small amount of glycogen. The yolk is synthesized in the liver of females in soluble form. Then through circulation, it is transported to the follicle cells that surround the maturing ovum.Yolk gets deposited in the form of yolk platelets and granules in ooplasm.The conversion of soluble form of yolk to platelets and granules brought about by Mitochondria and golgi complex. In insects, vitellogenesis starts with the release of juvenile hormone which is stimulated by the fat body and produces vitellogenin protein. In mammals, Vitellogenin is a major protein which is produced by Vit gene and it is regulated by oestrogen hormone.
Patterns of yolk deposition:
There are two patterns of yolk deposition. They are-
->Isolecithal – In this pattern yolk is sparse, and is evenly distributed.
->Telolecithal – In this pattern yolk is dense and present throughout most of the cell.
Brief introduction about the process of Vitellogenesis:
->In vitellogenesis, following steps occur. These are-
->Induction of vitellogenin synthesis with the help of hormones and then released in circulation.
->Transport of vitellogenin in the bloodstream to the target site.
->Uptake of vitellogenin by growing oocytes.
->Conversion of soluble vitellogenin into storage form.
->Therefore, from the above discussion it is clear that vitellogenesis occurs during the formation of primary oocytes in the graafian follicle.

Hence, the correct answer is option A.

Note: Point to be noted that developing offsprings of oviparous animals are entirely dependent on stored yolk for their survival. The nutrients are stored in the eggs that are laid by the oviparous animals.