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प्रश्न
Describe the process of oogenesis in human female.
Explain the process of oogenesis in humans.
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उत्तर
Oogenesis is a process of formation of the haploid female gamete i.e. egg or ovum from the diploid germinal epithelium. Oogenesis takes place in the ovaries and is initiated prior to birth of the female baby. It involves the process of mitosis and meiosis. This process can be divided into three stages:
- Multiplication phase: In this stage, the primary germinal cells - PGCs (2n) of ovary undergo repeated mitotic division to form millions of gamete mother cells or oogonial cells (2n). This process is completed in the embryonic stage of human females.
- Growth phase: Some of the oogonia stop division and begin to increase in size and form the primary oocytes (2n). Cellular organelles like ER, Golgi apparatus and mitochondria increase in number.
- Maturation phase:
- The primary oocytes (2n) enter the maturation phase, which includes meiotic division (Meiosis I and Meiosis II). The diploid primary oocytes undergo meiosis I (reduction division) to form two haploid daughter cells having 23 chromosomes. However, due to unequal division of cytoplasm, of the two daughter cells, one is a large cell, called secondary oocyte (n) and another is a small cell, called 1st polar body (n). Generally, the 1st polar body does not enter meiosis II.
- The secondary oocyte (n) proceeds only upto metaphase II of meiosis II and its division is further stopped or arrested at this stage. The secondary oocyte is shed from the Graafian follicle and ovary during ovulation. Meiosis II is completed only if fertilization occurs. This last phase is usually completed in the ampulla of the fallopian tube at the time of fertilization. In this division also, the two unequal daughter cells are formed i.e. the large cell is ovum (n) and the small cell is 2nd polar body (n). The ovum (n) so formed functions as the female gamete and is ready for fertilization. If the secondary oocyte is not fertilized by a sperm/spermatozoa, it is shed off along with menstruum.
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संबंधित प्रश्न
Define spermiogenesis.
Give scientific reason.
Older women are more likely to give birth to children with some abnormalities.
Describe the structure of the human ovum with a neat labelled diagram.
Expand the acronym.
LH
What is the location of oogenesis?
Conversion of spermatid into sperm is called as _______.
How many autosomes does a human primary spermatocyte have?
Which among the following has 23 chromosomes?
Identify the wrong statement from the following.
At the time of organogenesis, genes regulate the process at different levels and at different time due to ______.
Gray crescent is the area ______.
In spermatogenesis, reduction division of chromosome occurs during conversion of ______.
Read the following and answer from given below:
Oogenesis is the process of the formation of an ovum in the ovaries. It consists of three phases: multiplication, growth, and maturation. Oogenesis is controlled by hormones GnRH, LH, FSH. GnRH secreted by the hypothalamus stimulates the anterior lobe of the pituitary gland to secrete LH and FSH.
Which cell division is involved in the formation of secondary oocytes?
Sperms can be stored for several years in liquid nitrogen with a temperature of ______.
Fetal sex can be determined by examining cells from amniotic fluid looking for:
In the process of fertilization, this is true:
If for a species 2n = 16, then during Ist prophase and IInd prophase of the meiotic division of a cell, how many tetrads and diads will be formed:
Draw a labelled diagram of a section through the ovary.
The process of gametogenesis is initiated by ______ and ______ hormones respectively.
