In all living things reproduction is the criterion that makes life move from one generation to the other. Gametogenesis is that process which takes place both in the male and female sex. In gametogenesis, the formation of the male gametes (sex cells) and female gametes takes place separately. In biological terms, gametogenesis can be termed as the process in which a diploid cell divides and transforms into mature haploid gametes. Gametogenesis is of two types: Spermatogenesis and oogenesis. The major steps in gametogenesis are −
Spermatogenesis is the process through which immature germ cells are converted into sperms. It takes place in male testis. Within the testis, there is a seminiferous tubule which is the primary site for spermatogenesis. It involves several steps like cell division and differentiation which later produce a matured sperm.
Seminiferous tubules are found within the testis and the site for spermatogenesis. It is covered with Sertoli cells which are the somatic cells. It provides the necessary nourishment required for the maturation of sperm.
The fully functional male gametes are called spermatozoa and are present in sexually reproductive organisms.
Spermatogenic cells need to be around 2°C below the body temperature for proper functioning and it is regulated by the blood flow and the muscle positions that help to keep the scrotum away from the body heat.
In humans and animals, spermatogenesis similarly takes place.
In stage 1, primary spermatocytes cells are produced with half the genetic material. It is called spermatocytogenesis and 4 haploid spermatocytes are formed from single diploid cells.
Stem cells lined throughout seminiferous tubules undergo mitosis and form germ cells (spermatogonia). These germ cells that reach the Sertoli cells form large primary spermatocytes.
4 Haploid spermatids are formed from secondary spermatocytes through meiosis II in the second stage. It is called spermatidogenesis which takes place rapidly.
Spermiogenesis is the final stage where mature sperm cells or spermatozoa are formed from the spermatids.
Spermatozoa or the sperm cell has a head and a tail. The head is composed of genetic material and is covered with a thick cap-like structure called the acrosome. The tail is made of microtubules and is called axonema. The testosterone hormone present in the testis helps in the maturation of the sperm. The spermatozoa present in the Sertoli cells are moved into the seminiferous tubules but are non-motile and later move into the epididymis (structure behind the scrotum). It is stored within the epididymis and there it gains motility.
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Oogenesis takes place in females. It is the process in which a matured female gamete called the ovum is formed from the germ cells or oogonia in the ovary which are the female reproductive organs. Oogenesis starts before birth. At the embryonic stage, the production of primary oocytes takes place and stops. The further steps are processed after puberty. The periodic cycle that occurs every month in a female after puberty determines the reproductive life. It is called the menstrual cycle.
Oogenesis overall has 3 stages; follicular phase, ovulation phase and luteal phase.
When a female is born all the eggs that are released during the active reproductive years are ready in the ovaries.
Certain egg cells never mature and some get degenerated.
When a woman reaches the menopause stage, the process of oogenesis stops and the production of primary oocytes is stopped.
The process of oogenesis is regulated by the hormones of pituitary glands
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The process of oogenesis starts before birth and further development is arrested till puberty. At the time of puberty ovulation starts and the development of oogenesis restarts. The completion is achieved only after the fertilization of the ovum with sperm. The steps in oogenesis are as follows −
The diploid oogonium/ germ cell undergoes mitosis and forms diploid primary oocytes during the embryonic stage. Mitosis stops and it marks the beginning of meiosis.
At the prophase I of Meiosis, the further development of the primary oocyte is arrested. The primary oocytes are encircled with a sheet of follicular cells forming the primary follicle. From birth to puberty, a large number of primary follicles degenerate. Later the follicular cells form stratified columnar epithelium called granulosa cells. The primary oocytes get covered with several layers of granulosa cells resulting in the formation of secondary follicles.
After puberty, the primary oocytes undergo meiotic-I division resulting in the formation of haploid cells of unequal size. A large secondary oocyte and a smaller-sized cell are called a polar body.
Secondary oocytes now move on to the meiosis-II stage but it is arrested there. If the fertilization is meant to happen by the entry of sperm the secondary oocyte divides to form an ovum otherwise it degenerates and is removed through the menstrual cycle.
The secondary oocyte and ovum are haploid cells. The polar body formed first divides into two other polar bodies during oogenesis. If the sperm enters during the meiosis II stage the secondary oocyte forms the mature ovum which fertilizes with the sperm to form the zygote.
Division, Differentiation and maturation are the common steps involved in both spermatogenesis and oogenesis.
Germ cells are the precursor cells in both.
In both processes diploid cells form haploid gametes.
The meiotic division takes place in both processes.
The initial and most important stage of sexual reproduction.
| Spermatogenesis | Oogenesis |
|---|---|
| Process in which sperms are formed from spermatogonia | Ovum is produced from oogonia |
| Occurs in male testis | Occurs in female ovaries |
| The release of sperm takes place in million daily | One ovum is released in one monthly cycle |
| Occurs daily after puberty till the end | Starts after puberty and ends at the menopause stage |
| Occurrence of Sertoli cells | No Sertoli cells |
| Too short growth phase | Longer growth phase |
| Meiosis Ⅰ results in secondary spermatocytes | Meiosis Ⅰ results in secondary oocyte and polar body |
| Motile gametes are formed | Gametes are non-motile |
Spermatogenesis and oogenesis are 2 types of gametogenesis that are important stages of reproduction where the male gamete (sperm) and female gamete (ovum) is formed. Diploid cells are the start point where it ends with haploid cells. The formation of the male gamete takes place in the male testis and in the female, the ovum is formed in the ovaries. The sperm and ovum after gametogenesis undergo fertilization which later forms the zygote.
Q1. What is a polar body?
Ans. It is the product of meiotic division in oogenesis with little cytoplasm and a nucleus.
Q2. What is corpus luteum?
Ans. It is a mass of cells formed in the ovary and produces the hormone progesterone.
Q3. Which hormone induces spermatogenesis?
Ans. FSH - Follicle stimulating hormones
Q4. What is ovulation?
Ans. The release of an ovum from the ovary is termed ovulation.
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