Gametogenesis occurs once a haploid cell (n) is formed from a diploid cabinet (2n) v meiosis. We call gametogenesis in the male spermatogenesis and also it to produce spermatozoa.

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In the female, we speak to it oogenesis. It outcomes in the development of ova. This post covers both oogenesis and spermatogenesis.


In the beginning

Males start developing sperm when they reach puberty, i beg your pardon is usually from 10-16 years old. Biological males continually produce sperm in big quantities (~200 million a day). This maximises the likelihood the sperm reaching the egg adhering to ejaculation.

Sperm production occurs in the testes of the male, particularly in the seminiferous tubules. In the testicles, a blood-testis barrier forms to keep the tubules different from the systemic circulation.

Protecting the sperm

Sertoli cells form the blood-testis barrier. This is vital in staying clear of substances uncovered in blood indigenous affecting the developing sperm. These products might include hormones or garbage products.

It is also important together it stays clear of the immune system the the masculine from recognising the sperm as foreign – the sperm room genetically various from the male and also will express different surface antigens.

Forming functional sperm

Spermatogonia space the initial swimming pool of diploid cells that division by mitosis to provide two the same cells. One of these cells will be provided to replenish the swimming pool of spermatogonia – these cells are A1 spermatogonia. This replenishment the spermatogonia method that males are abundant throughout their adult life. The various other cell – type B spermatogonium – will certainly eventually form mature sperm.

Type B spermatogonia replicate by mitosis number of times to type identical diploid cells connected by cytoplasm bridges, these cells are now known as primary spermatocytes. Primary spermatocytes climate undergo meiosis.

Meiosis I produces 2 haploid cells, recognized as secondary spermatocytes.Meiosis II produces 4 haploid cells, well-known as spermatids.


The cytoplasmic bridges malfunction and the spermatids room released right into the lumen the the seminiferous tubule – a procedure called spermiation. The spermatids undergo spermiogenesis (remodelling and also differentiation right into mature spermatozoa) together they travel along the seminiferous tubules until they with the epididymis.

From the seminiferous tubule, cells will travel to the rete testis. This acts come “concentrate” the sperm by removing overfill fluid. Then, cells move to the epididymis wherein the sperm is stored and also undergoes the final stages of maturation.

Spermatogenesis take away approximately 70 days, thus in order for sperm production to be constant and no intermittent, multiple spermatogenic processes are developing simultaneously in ~ the very same seminiferous tubule, with brand-new groups of spermatogonia occurring every 16 work (spermatogenic cycle). Each of these populaces of spermatogenic cells will certainly be at different stages of spermatogenesis.

Following ejaculation

Note that once sperm leave the male body and enter the woman reproductive tract, the conditions there reason the sperm to undergo capacitation, i m sorry is the removal of cholesterol and also glycoproteins native the head of the sperm cell to allow it to bind to the zona pellucida that the egg cell.

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figure 1 – Diagram mirroring the overall process of spermatogenesis


Oogenesis different from spermatogenesis in that it begins in the foetus prior to birth. Primordial germ cells (which originate in the yolk sac of the embryo) move to colonise the cortex the the primordial gonad. Replication by mitosis peaks at approximately 7 million by mid-gestation (~20 weeks).

Cell fatality occurs ~ this optimal to leave 2 million cells. Meiosis i begins prior to birth and also forms primary oocytes. There is as such a finite it is provided of ova.

Primary oocytes space arranged in the gonads as clusters. They have flattened epithelial cells bordering them, and also this is called the primary follicle.

During childhood, more atresia (cell death) occurs, leaving ~40,000 egg at puberty.

Once puberty begins, a number of primary oocytes (15-20) start to mature every month, back only among these reaches complete maturation to become an oocyte.

The major oocytes undergo 3 stages:


Pre-Antral Stage

The main oocyte is still in meiosis I, yet will grow substantially in this stage. The follicular cells grow and proliferate to type a stratified cuboidal epithelium. Now, we contact these granulosa cells and also they secrete glycoproteins. This chemicals type the zona pellucida roughly the primary oocyte.

Surrounding connective organization cells also differentiates to end up being the theca folliculi, a specialty layer of bordering cells that is responsive to LH and can secrete androgens under the influence.

Antral Stage

Fluid to fill spaces type between granulosa cells, these eventually combine together to type a central fluid filled an are called the antrum.

We now contact the follicles secondary follicles. In every monthly cycle among these second follicles becomes dominant and also develops more under the affect of FSH, LH and also oestrogen. (See article on the menstrual cycle).

Pre-Ovulatory Stage

The LH surge induces this stage and also meiosis ns is now complete. Inside the follicle, 2 unequally size haploid cells form. Among the daughter cells receives far less cytoplasm than the other and also forms the first polar body, which will certainly not go on to form an ovum.

Another haploid cabinet is also formed, recognized as the secondary oocyte. Both daughter cells climate undergo meiosis II.

An early stage polar body will certainly replicate to offer two polar bodies but the an additional oocyte arrests in metaphase the meiosis II. This wake up 3 hrs prior to ovulation.


Now, the follicle has actually grown in size and also is mature – it is referred to as a Graafian follicle.

An LH surge occurs and also increases collagenase activity. This is an enzyme the disrupts collagen. Therefore, there is weakening the the follicular wall. This, merged with muscular contractions the the ovarian wall, outcomes in the ovum gift released from the ovary. The ovum is then taken up right into the fallopian tube via the fimbriae (finger-like projections of the fallopian tube).

Fertilisation – the final stage of female gametogenesis

The secondary oocyte will certainly only complete meiosis II complying with fertilisation. Here, it gives off a 3rd polar body. Following meiosis II, a fertilised egg results. If fertilisation doesn’t occurs, the oocyte degenerates 24 hrs after ovulation, remaining arrested in meiosis II.

If fertilisation does occur, peristaltic activities of the fallopian tube move the egg come the uterus wherein it have the right to implant into the posterior uterine wall.

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number 2 – chart demonstrating the overall procedure of oogenesis

Clinical Relevance

Polycystic Ovary Syndrome (PCOS)

PCOS is a common endocrine disorder that affects roughly 5-10% that premenopausal women. Overfill androgen production and the existence of multiple immature follicles in ~ a woman’s ovaries characterise this condition.

This problem has a poorly understood aetiology and patients can current with a wide variety of signs and also symptoms, including:

Oligomenorrhoea/amenorrhoeaInfertilityHirsutismObesityChronic pelvic painDepression

For diagnosis to take it place, 2 criteria listed below must it is in met:

Oligomenorrhoea and/or anovulation.Clinical/biochemical signs of hyperandrogenism.Polycystic ovaries top top imaging.

To regulate this, doctors need a patient centred approach. This have the right to include managing weight, to reduce hyperandrogenism and also using medications. Medications prescribed could be the combined dental contraceptive pill (to regulate oligo-/amenorrhoea) and metformin (to manage infertility).

Errors in Meiosis

Errors in gametogenesis have the right to lead to a number of chromosomal abnormalities consisting of non-disjunction or polyploidies. Non-disjunction occurs once chromosomes failure to different appropriately. Polyploidy occurs once there are much more than 2 duplicates of a homologous chromosome in a cell.

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Errors in gametogenesis have the right to lead to:

TrisomiesDown’s Syndrome – trisomy 21Edward’s Syndrome – trisomy 18Patau’s Syndrome – trisomy 13

Obstetricians can aid parents to display for chromosomal abnormalities antenatally.