What is spermatogenesis?
The production of male gametes, sperm, from testicular spermatogonia is called spermatogenesis. Spermatogonium is a diploid cell and found in the main reproductive organ, tubules of the testis, of humans. A spermatogonium is divided into four haploid cells through meiosis. Spermatogenesis starts at puberty with millions of sperms and lasts throughout life.
Spermatogonia are produced from germ cells which differentiated into primary spermatocytes which undergo first meiotic phase and produce haploid two secondary spermatocytes. These secondary spermatocytes develops through second meiotic phase to form four haploid sperms. Sperm development takes on average of 70 days time interval. 100 million of sperms are produced in the testis of humans during each day.
What is Oogenesis?
The production of female gametes, eggs, from oogonia in the ovary is called oogenesis. Primary oocytes are formed from oogonia through mitosis. During the process of meiosis, diploid primary oocyte is divided into a single egg. During each stage of meiosis, two polar bodies are produced. Oogensis occurs at puberty to menupause stage once in every month.
Oogenic germ cells are called oogonia, which are stem cells that renew themselves automatically and differentiate into eggs. Approximately 7 million germ cells are produced at embryonic development from thousands of oogonia from 2nd to 7 month of embryo. During embryonic development, primary oocytes which are formed through mitosis, developed to form deplotene in first meiotic division. Sometimes cell division ceased till puberty, but primary oocyte may also stop to divide till fifty years. Out of millions of primary oocytes, about 400 develops into gametes after puberty while rest of them are destroyed. At puberty, the arrested primary oocytes are converted into secondary oocyte and polar body. the cytoplasm of secondary oocyte is retained but nucleus of polar body is degraded. During ovulation, this secondary oocyte released from the ovary.
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Comparison table between spermatogenesis and oogenesis
In summary, here is a table showing the homologies between spermatogenesis and oogenesis.
|Comparison items||Spermatogenesis||Oogenesis |
|Number of gametes||Principle: Continuous neoformation|
Although sperm production occurs from puberty until death, it is subject to extreme fluctuations in quantity and quality.
|Principle: depletion of reserves|
Continuous exponential decrease in the number of ova since the fetal period. Depletion of reserves with menopause.
|Result of meiosis||At the end of meiosis, there are four functional gametes||At the end of meiosis, we find an oocyte and its three polar globules.|
|Fetal period||+ No onset of meiosis|
+ No germ cell production
|+ Entry into meiosis (arrested by dictyotene)|
+ Production of all germ cell reserves
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