Question

In which phase of the cell division is the oogonia arrested?
A. Anaphase II
B. Prophase I
C. Interphase
D. Both prophase I and II

Answer 1

Hint: Oogenesis is the process of the formation of female gametes called ovum or egg. The mother oocyte undergoes various divisions to form primary oocytes that get fertilized by sperm to form a zygote.

Complete answer:
Oogenesis is the process of the production of female gametes. The female gametes are called ovum or egg. Three major stages need to be completed by the mother oogonia cell to form a mature ovum. These stages are the multiplication phase, growth phase, and maturation phase. Let us understand each of these phases.

The multiplication phases involve the mitotic division of oogonia which is the mother gamete cell. A couple of million mother gamete cells are formed inside the fetal ovary during the embryonic stage. After birth, no more oogonia are formed. These oogonia start cell division and enter the prophase I of the meiotic cell division. These cells are now called primary oocytes. They get temporarily arrested at this stage till ovulation starts in puberty. The growth phase is characterized by the formation of a layer around the primary oocytes. This layer is formed by granulosa cells and the complex formed is called the primary follicle.

At puberty only around 60,000 to 80,000 primary follicles are left due to continuous degeneration. More layers develop to surround the primary follicles. This results in the formation of a secondary follicle. The maturation phase is the last. It is divided into two sub-phases. In the first maturation phase, the secondary follicle is converted into a tertiary follicle.

At this stage, the primary oocyte inside this tertiary follicle completes its first meiotic division and forms a secondary oocyte. Now, the tertiary follicle becomes mature and is called the graafian follicle. This follicle ruptures and releases the secondary oocyte during ovulation. The second maturation phase happens after the fertilization of the egg or ovum. Therefore, from the above discussion, we can conclude that the primary oocyte is arrested at the Prophase-I stage of meiosis I cell division.

Hence, option B is the correct answer.

Note: The recent discoveries have allowed scientists to understand the process of gamete formation in more detail. Scientists are now able to form male gametes by stem cells. Research is going to confirm the formation of oogonia after the birth of the female child. If it happens then the whole reproductive biology field will be changed.