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An oocyte, ovocyte, or rarely ocyte, is a female gametocyte
Gametocyte

A gametocyte is a eukaryotic germ cell that divides by mitosis into other gametocytes or by meiosis into gametids during gametogenesis. Male gametocytes are called spermatocytes, and female gametocytes are called oocytes....
 or germ cell
Germ cell

Germ cells are progenitors of the gametes. These singled-out cells move through the gut to the developing gonads and undergo mitotic Cell proliferation followed by meiosis and Cellular differentiation into either eggs or sperm ....
 involved in reproduction
Biological reproduction

Reproduction is the biological process by which new individual organisms are produced. Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction....
. In other words, it is an immature ovum
Immature ovum

An immature ovum is a cell that goes through the process of oogenesis to become an ovum. It can be either an oogonium, oocyte and an ootid. An oocyte, in turn, can be either primary or secondary, depending on how far it has come in its process of meiosis....
, or egg
Ovum

An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization....
 cell. An oocyte is part of the ovary development. The germ cells produce a primordial germ cell (PGC) which becomes an oogonium which marks the start of mitosis
Mitosis

Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei....
. After mitosis stops (due to actions of retinoic acid and the mesenephros) meiosis
Meiosis

In biology or life science, meiosis is a process of reductional division in which the number of chromosomes per cell is halved. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores....
 starts. This stage the oogonia is now an Oocyte (pronounced oh'a-site).

formation of an oocyte is called oocytogenesis, which is a part of oogenesis.






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An oocyte, ovocyte, or rarely ocyte, is a female gametocyte
Gametocyte

A gametocyte is a eukaryotic germ cell that divides by mitosis into other gametocytes or by meiosis into gametids during gametogenesis. Male gametocytes are called spermatocytes, and female gametocytes are called oocytes....
 or germ cell
Germ cell

Germ cells are progenitors of the gametes. These singled-out cells move through the gut to the developing gonads and undergo mitotic Cell proliferation followed by meiosis and Cellular differentiation into either eggs or sperm ....
 involved in reproduction
Biological reproduction

Reproduction is the biological process by which new individual organisms are produced. Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction....
. In other words, it is an immature ovum
Immature ovum

An immature ovum is a cell that goes through the process of oogenesis to become an ovum. It can be either an oogonium, oocyte and an ootid. An oocyte, in turn, can be either primary or secondary, depending on how far it has come in its process of meiosis....
, or egg
Ovum

An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization....
 cell. An oocyte is part of the ovary development. The germ cells produce a primordial germ cell (PGC) which becomes an oogonium which marks the start of mitosis
Mitosis

Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei....
. After mitosis stops (due to actions of retinoic acid and the mesenephros) meiosis
Meiosis

In biology or life science, meiosis is a process of reductional division in which the number of chromosomes per cell is halved. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores....
 starts. This stage the oogonia is now an Oocyte (pronounced oh'a-site).

Formation

The formation of an oocyte is called oocytogenesis, which is a part of oogenesis. Oogenesis results in the formation of both primary oocytes before birth, and of secondary oocytes after it as part of ovulation
Ovulation

Ovulation is the process in the menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum that participates in reproduction....
.

Cell type ploidy
Ploidy

Ploidy is the number of complete sets of non-homologous chromosomes in a biological cell. In humans, the somatic cells that comprise the body are diploid , but sex cells are haploid....
/chromosomes 		chromatids Process Time of completion >- | Oogonium
Oogonium

An oogonium is an immature ovum. It is a female gametogonium. They are formed in large numbers by mitosis early in fetus life from germ cells, which are present in the fetus between weeks 4 and 8....
 		 diploid/46 2N Oocytogenesis (mitosis
Mitosis

Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei....
) 		third trimester
Trimester

Trimester means a period of three months. It is most commonly used in physiology related to pregnancy and at some universities to describe an academic term....
 |- | primary Oocyte 		diploid/46 4N Ootidogenesis (meiosis
Meiosis

In biology or life science, meiosis is a process of reductional division in which the number of chromosomes per cell is halved. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores....
 1) (Folliculogenesis
Folliculogenesis

In biology, folliculogenesis is the maturation of the ovarian follicle, a densely-packed shell of somatic cells that contains an immature oocyte....
) 		Dictyate
Dictyate

The dictyate or dictyotene is a prolonged resting phase in oogenesis. It occurs in the stage of meiotic prophase I in ootidogenesis. It starts late in fetal life and is terminated shortly before ovulation by the LH surge....
 in prophase I until ovulation |- | secondary Oocyte 		haploid/23 2N Ootidogenesis (meiosis
Meiosis

In biology or life science, meiosis is a process of reductional division in which the number of chromosomes per cell is halved. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores....
 2) 		- | Ootid haploid/23 1N ? - | Ovum
Ovum

An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization....
 		 haploid/23 1N  


Characteristics


Cytoplasm

Oocytes are rich in cytoplasm
Cytoplasm

The cytoplasm is the part of a Cell that is enclosed within the plasma membrane. In eukaryote cells the cytoplasm contains organelles, such as mitochondrion, that are filled with liquid kept separate from the rest of the cytoplasm by biological membranes....
 which contains yolk granules to nourish the cell early in development.

Nucleus

During the primary oocyte stage of oogenesis, the nucleus is called a germinal vesicle

The only normal human type of secondary oocyte has sex chromosomes 23,X (where sperm can be 23,X or 23,Y).

Nest

The space wherein an ovum or immature ovum is located is the cell-nest.

Abnormalities

  • nondisjunction
    Nondisjunction

    Nondisjunction is the failure of chromosome pairs to separate properly during cell division. This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis....
     -- a failure of proper homolog separation in meiosis I, or sister chromatid
    Chromatid

    A chromatid is one among the two identical copies of DNA making up a replicated chromosome, which are joined at their centromeres, for the process of cell division ....
     separation in meiosis II can lead to aneuploidy
    Aneuploidy

    Aneuploidy is defined as an abnormal number of chromosomes. Syndromes caused by an extra or missing chromosome are among the most widely recognized genetic disorders in humans....
    , in which the oocyte has the wrong number of chromosomes, for example 22,X or 24,X. This is the cause of conditions like Down syndrome
    Down syndrome

    Down syndrome, Down's syndrome, or trisomy 21 is a chromosomal disorder caused by the presence of all or part of an extra chromosome 21 ....
     and Edwards syndrome
    Edwards syndrome

    Trisomy 18 or Edwards Syndrome is a genetic disorder caused by the presence of all or part of an extra chromosome 18 . It is named after John H....
    . It is more likely with advanced maternal age.
  • Some oocytes have multiple nuclei
    Cell nucleus

    In cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in all eukaryote cell ....
    , although it is thought they never mature.


Resources

William K. Purves, Gordon H. Orians, David Sadava, H. Craig Heller, Craig Heller (2003). Life: The Science of Biology(7th ed.), pp. 823–824

See also

  • Folliculogenesis
    Folliculogenesis

    In biology, folliculogenesis is the maturation of the ovarian follicle, a densely-packed shell of somatic cells that contains an immature oocyte....
  • polar body
    Polar body

    A polar body is a cell structure found inside an ovum. Both animal and plant ova possess it. It is also known as a polar cell.Asymmetrical cell division leads to the production of polar bodies during oogenesis....


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