Question

What is oogenesis? Give a brief account of oogenesis.

Answer 1

The process of formation of a mature female gamete is called oogenesis. In contrast to spermatogenesis (in males), oogenesis begins in females before they are even born.

Complete answer:
The process of formation of female gametes is known as oogenesis. It occurs in the outermost layers of the ovary. There are three stages in the process of oogenesis.
Pre natal stage
The cell of germinal epithelium of the ovary divides by mitosis, providing undifferentiated germ cells called egg mother cells or oogonia in the foetus ovary. The oogonia multiplies by mitotic divisions and projects into the stoma of the ovary as a cord. One cell in the egg nest grows and becomes the primary oocyte. Meiosis begins in the primary oocyte soon after their formation. However, the oocytes are arrested in the early part of meiotic prophase I (diplotene stage).
Antral stage
Primary oocytes get surrounded by layers of granulosa cells and are called primary follicle. Primary follicles get surrounded by more layers of granulosa cells and the new theca and are called secondary follicles. The secondary follicle soon transforms into a tertiary follicle, which is characterized by a fluid filled cavity called antrum. the secondary follicles develop under the influence of hormones like Luteinizing hormone and Follicle stimulating hormone.
Preovulatory stage
At this stage the primary oocyte grows in size and completes first meiotic division and forms a large haploid secondary oocyte and a tiny first polar body. First polar body divides to form two second polar bodies by the second meiotic division. The secondary oocyte again divides into unequal daughter cells, a large ootid and a very small second polar body. The ootid grows into functional haploid ovum.

Note: Ovulation is the process by which the secondary oocyte is released from the ovaries. The process happens because when a follicle attains maturity and forms secondary oocytes finally. Then, the follicle breaks and a secondary oocyte is released into the fallopian tubes.