Oogenesis or rarely oögenesis is the creation of an ovum (egg cell). An ovum (plural ova) is a Haploid Female reproductive cell or Gamete. It is the female process of gametogenesis. Gametogenesis is a process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid Gametes Depending on the Biological It involves the various stages of immature ova. An immature ovum is a cell that goes through the process of Oogenesis to become an Ovum.

Contents 1 Oogenesis in mammals 1.1 Creation of oogonia 1.2 Oocytogenesis 1.2.1 Number of primary oocytes 1.3 Ootidogenesis 1.3.1 Meiosis I 1.3.2 Meiosis II 1.3.3 Folliculogenesis 1.4 Maturation into ovum 2 Oogenesis in non-mammals 3 See also 4 References 5 External links

Oogenesis in mammals

In mammals, oogenesis occurs in the ovarian follicle of the ovary. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Ovarian follicle is the basic unit of female reproductive biology and is composed of a roughly spherical aggregations of cells found in the Ovary. "Ovaria" redirects here This is also a proposed section and a Synonym of Solanum.

It is interesting to note that such an important process in animal life cycles is done completely without the aid of spindle-coordinating centrosomes. In Cell biology, the spindle apparatus (also called spindle fibers) is the structure that separate the Chromosomes into the daughter cells during In Cell biology, the centrosome is an Organelle that serves as the main Microtubule organizing center (MTOC of the animal cell as well

It consists of several processes: oocytogenesis, ootidogenesis and the final maturity to form an ovum. Oogenesis or rarely oögenesis is the creation of an Ovum (egg cell Folliculogenesis is a separate process during ootidogenesis. In Biology, folliculogenesis is the maturation of the Ovarian follicle, a densely-packed shell of Somatic cells that contains an immature Oocyte

Cell type	ploidy	Process	Process completion
Oogonium	diploid	Oocytogenesis (mitosis)	third trimester (forming oocytes)
primary Oocyte	diploid	Ootidogenesis (meiosis 1) (Folliculogenesis)	Dictyate in prophase I until ovulation
secondary Oocyte	haploid	Ootidogenesis (meiosis 2)	Halted in metaphase II until fertilization
Ootid	haploid	?	Minutes after fertilization
Ovum	haploid

Creation of oogonia

The creation of oogonia traditionally doesn't belong to oogenesis, but to the common path of gametogenesis together with spermatogenesis. "Haplo" redirects here For the fictional character see The Death Gate Cycle. An oogonium (plural oogonia) is an Immature ovum. It is a female Gametogonium. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei Pregnancy ( Latin graviditas) is the carrying of one or more offspring known as a Fetus or Embryo, inside the Uterus of a Female An oocyte, ovocyte, or rarely ocyte, is a female Gametocyte or Germ cell involved in reproduction. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half In Biology, folliculogenesis is the maturation of the Ovarian follicle, a densely-packed shell of Somatic cells that contains an immature Oocyte The dictyate or dictyotene is a prolonged resting phase in Oogenesis. An oocyte, ovocyte, or rarely ocyte, is a female Gametocyte or Germ cell involved in reproduction. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half An immature ovum is a cell that goes through the process of Oogenesis to become an Ovum. An ovum (plural ova) is a Haploid Female reproductive cell or Gamete. Gametogenesis is a process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid Gametes Depending on the Biological

Oocytogenesis

Oogenesis starts with oogonial transformation into primary oocytes, called oocytogenesis^[1]. An oogonium (plural oogonia) is an Immature ovum. It is a female Gametogonium. An oocyte, ovocyte, or rarely ocyte, is a female Gametocyte or Germ cell involved in reproduction. Oocytogenesis is completed either before or shortly after birth.

Number of primary oocytes

It is commonly said that when oocytogenesis is completed, no additional primary oocytes are created, in contrast to the male spermatogenesis, where gametocytes are continuously created. In other words, oocytes reaches their maximum at ~20^[2][3] Renewal of ovarian follicles from germline stem cells (originating from bone marrow and peripheral blood) was reported in the postnatal mouse ovary. Due to the revolutionary nature of these claims, further experiments are required to examine the dynamics of small follicle formation.

Ootidogenesis

The succeeding ootidogenesis is the step in which the primary oocyte turns into an ootid. An oocyte, ovocyte, or rarely ocyte, is a female Gametocyte or Germ cell involved in reproduction. It is achieved by meiosis. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half The primary oocyte is even defined from its role to undergo meiosis^[4].

However, although this process begins at prenatal age, it stops at prophase I. In late fetal life, all oocytes, still primary oocytes, have taken this halt in development, called dictyate. The dictyate or dictyotene is a prolonged resting phase in Oogenesis. First after menarche they continue to develop, although only a few does so every menstrual cycle.

Meiosis I

Meiosis I of ootidogenesis starts at embryonic age, but halts in diplotene of prophase I until puberty. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half For those primary oocytes continuing to develop in each menstrual cycle, however, synapsis occurs and tetrads form, enabling and crossing over. As a result of meiosis I, the primary oocyte becomes the secondary oocyte and the first polar body. An oocyte, ovocyte, or rarely ocyte, is a female Gametocyte or Germ cell involved in reproduction. A polar body is a cell structure found inside an Ovum. Both Animal and Plant ova possess it

Meiosis II

Immediately after meiosis I, the haploid secondary oocyte initiates meiosis II. However, this, too is halted in metaphase II. However, this only lasts until fertilization, if such occurs. For soil improvement see Fertilization (soil. When meiosis II is completed, an ootid and another polar body is created.

Folliculogenesis

Main article: Folliculogenesis

Synchronously as ootidogenesis, the ovarian follicle surrounding it develops from a primordial follicle to a preovulatory one. In Biology, folliculogenesis is the maturation of the Ovarian follicle, a densely-packed shell of Somatic cells that contains an immature Oocyte Ovarian follicle is the basic unit of female reproductive biology and is composed of a roughly spherical aggregations of cells found in the Ovary.

Maturation into ovum

Both polar bodies at the end of Meiosis II disintegrate leaving only the ootid which undergoes maturation and eventually matures into an ovum.

Oogenesis in non-mammals

Many protists produce egg cells in structures termed archegonia. Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this An archegonium (pl archegonia) from the Ancient Greek ἀρχή ("beginning" and γόνος ("offspring" is a multicellular Some algae and the oomycetes produce eggs in oogonia. Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms Oomycetes also known as Water molds (or water moulds: see spelling differences) are a group of filamentous unicellular Heterokonts physically An oogonium (plural oogonia) is an Immature ovum. It is a female Gametogonium. In the brown alga Fucus, all four egg cells survive oogenesis, which is an exception to the rule that generally only one product of female meiosis survives to maturity. Fucus is a Genus of Brown alga ( Seaweed) in the Class Phaeophyceae to be found in the intertidal zones of rocky shores

In plants, oogenesis occurs inside the female gametophyte via mitosis. Plants are living Organisms belonging to the kingdom Plantae. In Plants and Algae that undergo Alternation of generations, a gametophyte is the multicellular structure or phase that is Haploid, containing Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei In many plants such as bryophytes, ferns, and gymnosperms, egg cells are formed in archegonia. Bryophytes are all Embryophytes ('land Plants) that are non-vascular: they have tissues and enclosed reproductive systems but they lack Vascular tissue A fern is any one of a group of about 20000 Species of Plants classified in the phylum or division Pteridophyta, also known as Filicophyta Gymnosperm (Gymnospermae are a group of Spermatophyte seed-bearing Plants with Ovules on the edge or blade of an open Sporophyll, which are An archegonium (pl archegonia) from the Ancient Greek ἀρχή ("beginning" and γόνος ("offspring" is a multicellular In flowering plants, the female gametophyte has been reduced to an eight-celled embryo sac within the ovule inside the ovary of the flower. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group Ovule literally means "small egg." In Seed plants the ovule is the structure that gives rise to and contains the female reproductive cells Ovule literally means "small egg." In Seed plants the ovule is the structure that gives rise to and contains the female reproductive cells In the Flowering plants an ovary is a part of the female reproductive organ of the flower or Gynoecium. Oogenesis occurs within the embryo sac and leads to the formation of a single egg cell per ovule.

In ascaris, the oocyte does not even begin meiosis until the sperm touches it, in contrast to mammals, where meiosis is completed in the menstrual cycle. Ascaris is a genus of parasitic Nematode worms One species A suum, typically infects Pigs, while another The term sperm is derived from the Greek word (σπέρμα sperma (meaning "seed" and refers to the male reproductive cells.

See also

• Oogonium
• Archegonium
• Oocyte
• Spermatogenesis

References

External links

• http://distance.stcc.edu/AandP/AP/AP2pages/reprod/oogenesi.htm
• Reproductive Physiology

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