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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
Draw a labelled diagram of sperm.
Sex organs produce gametes which are diploid.
The male sex hormone testosterone is secreted from ____________.
Mammalian egg is ____________.
The process which the sperm undergoes before penetrating the ovum is ____________.
The following is the illustration of the sequence of ovarian events (a-i) in a human female.
Identify the figure that illustrates ovulation and mention the stage of oogenesis it represents.
Formation of ____________ is an indication of the termination of oogenesis.
Which of the following occurs during maturation phase of spermatogenesis?
Find out the CORRECT sequence of spermatogenesis.
The human male gamete is usually about ______ in length.
How many sperms are formed from a secondary spermatocyte?
Which of the following stage of oogenesis forms a membrane called zona pellucida surrounding it?
The immature male germ cell undergo division to produce sperms by the process of spermatogenesis.
Choose the correct one with reference to the above.
At what stage of life is oogenesis initiated in a human female?
In the process of fertilization, this is true:
Human milk differs from cow's milk because human milk contains:
Given below are two statements.
- Statement I: The spermatids are non-motile and non-functional which get transformed into functional spermatozoa by the process of spermiogenesis.
- Statement II: During the process of this change, the spermatids remain held to each other and to Leydig's cells by cytoplasmic bridges.
In light of the above statements, select the correct answer from the option given below.
Sketch and label the process of oogenesis.
The diagram given below shows the various steps in spermatogenesis.
- Name the parts labelled '1', '2' and '3'.
- Name the process by which part '3' changes to part '4'.
Select a correct pair of cells with identical set of chromosomes.
