GAMETOGENESIS : OOGENESIS

 

Gametogenesis –Oogenesis:  Gametogenesis is the process of formation of gametes. It is divided into two parts - Spermatogenesis and Oogenesis. Spermatogenesis is the formation of sperms and Oogenesis is the formation of egg or ova.

The process of formation of mature female gamete is called oogenesis.   It is divided into following stages ;

a)Multiplication Phase

b)Growth Phase

c) Maturation phase

Multiplication Phase –At the time of fetus development inside the mother’s womb there is the occurrence of another development in female that is the development of Egg mother cells or oogonia. No more oogonia are formed and added after birth. The egg mother cells or oogonia are larger cells with large nuclei and other constituents. These cells undergo mitosis division and increases in number. Oogonia are diploid or 2n having 46 chromosomes. Oogonial cells after the formation in huge number project into the stroma as a cord then becomes a round mass called the egg nest. One of the cell of the egg nest grows and becomes the primary oocytes. It is the future ovum. Other oogonia surrounds around the primary oocytes   to protect and give nourishment. Primary oocytes cells starts division and enters into the prophase I of the meiotic division but get temporarily arrested at this stage.

Growth Phase- In the growth phase development of primary oocytes takes place. Here along with the development of primary oocytes , follicle development also takes place. So this phase shows the development of Graulosa cells, Primary follicles, theca cells , secondary follicles etc.  It is a very long phase.

Maturation phase : In this phase, Primary oocytes completes its first meiosis and then second meiosis. In meiosis cell division there is the occurrence of 4 cells, here also it occurs but are all the cells that are formed not same. Out the four cells that develop here, 3 are small and is called as polar bodies and one is only big that is the egg or ootid.

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