Gametogenesis
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213537607
2008-05-19T19:53:48Z
Prim Ethics
7122743
Undo change of 28 February 2008
'''Gametogenesis''' is a process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid [[gamete]]s. Depending on the [[biological life cycle]] of the organism, gametogenesis occurs by [[meiosis|meiotic]] division of diploid [[gametocyte]]s into various gametes or by [[mitosis|mitotic]] division of haploid gametogenous cells. For example, plants produce gametes through mitosis in [[gametophyte]]s. The gametophytes grow from haploid spores after sporic meiosis. The existence of a multicellular, haploid phase in the life cycle between meiosis and gametogenesis is also referred to as [[alternation of generations]].
==Gametogenesis in animals==
[[Image:Gray7.png|thumb|400px|Scheme showing analogies in the process of maturation of the ovum and the development of the spermatids, following their individual pathways. The oocytes and spermatocytes are both gametocytes. Ova and spermatids are complete gametes.]]
Animals produce gametes directly through meiosis in organs called [[gonad]]s. [[Male]]s and [[female]]s of a species that [[sexual reproduction|reproduces sexually]] have different forms of gametogenesis:
* '''[[spermatogenesis]]''' (male)
* '''[[oogenesis]]''' (female)
===Stages===
However, before turning into gametogonia, the embryonic development of gametes is the same in males and females.
====Common path====
Gametogonia are usually seen as the initial stage of gametogenesis. However, gametogonia are themselves successors of [[primordial germ cells]]. During early embryonic development, primordial germ cells (PGCs) from the dorsal [[endoderm]] of the [[yolk sac]] migrate along the hindgut to the [[gonadal ridge]]. They multiply by [[mitosis]] and once they have reached the gonadal ridge they are called gametogonia. Gametogonia are not longer the same between males and females.
====Individual path====
From gametogonia, male and female gametes develop differently - males by [[spermatogenesis]] and females by [[oogenesis]]. However, by convention, the following pattern is common for both:
{| class="wikitable"
| '''Cell type''' || '''[[ploidy]]/[[chromosomes]]''' || '''[[chromatids]]''' || '''Process'''
|-
| [[gametogonium]] || diploid/46 || 2N || [[gametocytogenesis]] ([[mitosis]])
|-
| primary [[gametocyte]] || diploid/46 || 4N || [[gametidogenesis]] ([[meiosis]] 1)
|-
| secondary [[gametocyte]] || haploid/23 || 2N || [[gametidogenesis]] ([[meiosis]] 2)
|-
| [[gametid]] || haploid/23 || 1N ||
|-
| [[gamete]] || haploid/23 || 1N ||
|}
==Gametogenesis in gametangia==
Fungi, algae and primitive plants form specialized haploid structures called [[gametangium|gametangia]] where gametes are produced through mitosis. In some fungi, for example [[zygomycota]], the gametangia are single cells on the end of [[hypha]]e and acting as gametes by fusing into a [[zygote]]. More typically, gametangia are multicellular structures that differentiate into male and female organs:
* '''[[antheridium]]''' (male)
* '''[[archegonium]]''' (female)
==Gametogenesis in flowering plants==
In flowering plants, the male gamete is produced inside the [[pollen|pollen grain]] through the division of a generative cell into two sperm nuclei. Depending on the species, this can occur while the pollen forms in the [[anther]] or after [[pollination]] and growth of the [[pollen tube]]. The female gamete is produced inside the [[embryo sac]] of the [[ovule]].
{{Reproductive physiology}}
[[Category:Developmental biology]]
[[Category:Reproductive system]]
[[Category:Germ cells]]
[[de:Gametogenese]]
[[es:Gametogénesis]]
[[fr:Gamétogenèse]]
[[lv:Gametoģenēze]]
[[mk:Гаметогенеза]]
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[[pl:Gametogeneza]]
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[[ru:Гаметы]]
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[[sr:Гаметогенеза]]
[[th:การเกิดเซลล์สืบพันธุ์]]