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| Immature ovum | |
|---|---|
| Anatomical terminology |
Animmature ovum is a cell that goes through the process ofoogenesis to become anovum. It can be anoogonium, anoocyte, or anootid. An oocyte, in turn, can be either primary or secondary, depending on how far it has come in its process ofmeiosis.
| Cell type | ploidy/chromosomes | chromatids | Process | Process completion |
|---|---|---|---|---|
| Oogonium | diploid/46 | 2C | Oocytogenesis (mitosis) | third trimester |
| primary Oocyte | diploid/46 | 4C | Ootidogenesis (meiosis 1) (Folliculogenesis) --polar body separated | Dictyate in prophase I until ovulation |
| secondary Oocyte | haploid/23 | 2C | Ootidogenesis (meiosis 2) --polar body separated | Halted in metaphase II until fertilization |
| Ootid | haploid/23 | 1C | Maturation | Minutes after fertilization |
| Ovum | haploid/23 | 1C |
Oogonia are the cells that turn into primary oocytes in oogenesis.[1] They are diploid.
Oogonia are created in earlyembryonic life. All have turned into primary oocytes at late fetal age.
The primary oocyte is defined by its process ofootidogenesis, which is meiosis.[2] It has duplicated its DNA, so that each chromosome has two chromatids, i.e. 92 chromatids all in all (4C).
When meiosis I is completed, one secondary oocyte and onepolar body is created.
Primary oocytes have been created in late fetal life. This is the stage where immature ova spend most of their lifetime, more specifically in diplotene of prophase I of meiosis. The halt is calleddictyate. Most degenerate byatresia, but a few go throughovulation, and that's the trigger to the next step. Thus, an immature ovum can spend up to ~55 years as a primary oocyte (the last ovulation beforemenopause).
The secondary oocyte is the cell that is formed by meiosis I in oogenesis.[3] Thus, it has only one of each pair of homologous chromosomes. In other words, it is haploid. However, each chromosome still has two chromatids, making a total of 46 chromatids (1N but 2C). The secondary oocyte continues the second stage of meiosis (meiosis II), and the daughter cells are one ootid and onepolar body.
Secondary oocytes are the immature ovum shortly after ovulation, tofertilization, where it turns into an ootid. Thus, the time as a secondary oocyte is measured in days.
Anootid is the haploid result of ootidogenesis.[4] In oogenesis, it doesn't really have any significance in itself, since it is very similar to the ovum. However, it fills the purpose as the female counterpart of the malespermatid inspermatogenesis.
Each chromosome is split between the two ootids, leaving only one chromatid per chromosome. Thus, there are 23 chromatids in total (1N).
The ootid matures into anovum.