Gametogenesis is the production process of gametes. THE spermatogenesis is the name given to the process of gametogenesis in which male gametes are produced, the sperm. oogenesis is the name given to the process of gametogenesis in which the female gametes, the oocytes.
→ How and where does gametogenesis take place?
Gametogenesis basically occurs through the process of division and maturation of gametes. From diploid cells, the processes of mitosis and meiosis produce the haploid gametes.
Female gametogenesis takes place in ovaries. The male gametogenesis, in the testicles. It is important to highlight that the processes of cell division and maturation occur within the seminiferous tubules.
Read too: Difference between mitosis and meiosis
→ spermatogenesis
The process of gametogenesis in man, that is, the process of formation and development of sperm, is called spermatogenesis. Around the eighth week of gestation, the male embryo presents germ cells that in the future generate the sperm.
However, just next to puberty, these cells undergo transformations stimulated by sex hormones and form the spermatogonia. At spermatogonia are produced from germ cells through mitosis. Spermatogonia can be classified into type A and B.
Type A spermatogonia produce new throughout the individual's life. spermatogonia, by the process of mitosis. This phase is called multiplication phase. Type B spermatogonia produce the spermatocytes by the process of meiosis. Each spermatogonia produces a spermatophyte.
Type B spermatogonia, during the interphase phase of meiosis, give rise to primary spermatophytes. This is growth stage. In this process, type B spermatogonia increase in size, causing the genetic material to multiply.
These spermatophytes then generate the secondary spermatophytes, after going through the first division that occurs in the meiosis process. On the other hand, spermatocytes II, after going through the second division that occurs in the meiosis process, give rise to spermatids. The phase corresponding to the two periods of cell division that give rise to spermatids is called maturation stage.
Spermatids are haploid cells (n = 23 chromosomes) and show half of the chromosomes presented in the original cell, which was a diploid cell (2n = 46 chromosomes). Four spermatids are produced from each spermatocyte. Then the spermatids undergo some transformations and give rise to sperm. This last step is called spermiogenesis.
In spermiogenesis, spermatids go through a process of morphological differentiation, giving rise to a flagellated and mobile cell, the sperm. It also has a head, where its core is, and a region, called the acrosome, containing enzymes that help in the process of fertilization. Just behind the head are the mitochondria, which provide the energy needed for this cell to move. When spermiogenesis is complete, sperm are released into the lumen of the seminiferous tubules. This process is called spermiation.
Spermatogenesis is the process of gamete production in man. Oogenesis, on the other hand, is the process of production of gametes in women.
Read too: What is fertilization?
→ oogenesis
oogenesis it is the process of producing female gametes. This is a process that starts in embryonic life, unlike spermatogenesis – which starts close to puberty. The cell division process by mitosis occurs in germ cells around the seventh week of gestation, producing the oogonia.
Then, in the second trimester of pregnancy, the oogonias begin the process of meiosis, becoming known as primary oocytes. However, this process ceases before birth, during the prophase I, and it only continues from the ovulation. The first ovulation occurs at the beginning of the puberty.
It is believed that women are already born with all their primary oocytes, about two million. However, some studies suggest that, in fact, from stem cells, new gametes can form in adult women. The primary oocytes remain at rest within structures called follicles until ovulation, when she completes the first meiotic division.
Ovulation occurs in each menstrual cycleof the woman, throughout her reproductive life, which continues until around 50 years of age, a phase called menopause. In each cycle, about 50 follicles are stimulated to continue their development, however, only one primary oocyte completes the first meiotic division, the others suffer apoptosis (cell death).
O secondary oocyte it is a polar corpuscle appear at the end of the first meiotic division. The second meiotic division then begins, but there is a new resting phase, which begins in the metaphase II phase and remains until the secondary oocyte is fertilized by a sperm.
The oocyte, after its release from the ovary, remains viable for about 24 hours. occurring to fertilization, the oocyte gives rise to the egg and a second polar body. It is noteworthy that the formed corpuscles are degenerate. If there is no fertilization, the oocyte suffers autolysis (the process by which a cell spontaneously self-destructs).
occurring to fertilization, the follicle that ruptured releasing the oocyte forms the corpus luteum, which produces the calls hormones of pregnancy, that is, hormones responsible for maintaining pregnancy in the early period: estrogens and progesterone. This role is performed by the placenta after the second month of pregnancy. If fertilization does not occur, the corpus luteum degenerates.
Read too: Menstruation, what is it and how does it occur?
→ Differences between spermatogenesis and oogenesis
The processes of spermatogenesis and oogenesis have the following differences:
In oogenesis, the cell division process does not occur in the same way, so a large cell is formed, a single gamete (oocyte), and the other formed cells, of smaller size and called polar corpuscles, degenerate. In the spermatogenesis process, in the end, four gametes are formed.
The oogenesis process, until reaching the production of the mature gamete, is not continuous, with long periods of interruption. However, this does not occur in spermatogenesis, as this is a continuous process.
The oogenesis process ends around the age of 50 of the individual, in a phase known as menopause. Spermatogenesis occurs practically throughout the individual's life, producing mature gametes.
→ Solved exercises on gametogenesis
Question 1 - (PUC-Campinas) The following figures represent gametogenesis processes in animals.
Assuming that this is human gametogenesis, it is correct to conclude that:
a) cells with 46 chromosomes exist only in period 1.
b) meiotic divisions occur in periods 2 and 3.
c) from a spermatogonia, two primary spermatocytes are formed.
d) each primary oocyte gives rise to a secondary oocyte.
e) fertilization takes place during period 4.
Resolution: letter D. At the end of the first meiotic division, the primary oocyte gives rise to a secondary oocyte and a polar body. The polar body subsequently degenerates.
Question 2 - (PUC-Campinas) The following diagram represents phases of gametogenesis.
I and II correspond, respectively, to
a) two successive mitoses.
b) two successive meioses.
c) a mitosis and a meiosis.
d) meiosis I and meiosis II.
e) a meiosis and a mitosis.
Resolution: letter D. The processes shown in the figure represent meiosis I, in which the first cell division occurs, and meiosis II, in which the second cell division occurs. From a single cell, four new ones emerge.
