Editing Gamete

{{Short description|Haploid sex cell}}
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A '''gamete''' ({{IPAc-en|ˈ|ɡ|æ|m|iː|t}}; {{etymology|grc|''{{wikt-lang|grc|γαμετή}}'' ({{grc-transl|γαμετή}})|wife}}, ultimately {{etymology|grc|''{{wikt-lang|grc|γάμος}}'' ({{grc-transl|γάμος}})|marriage}}) is a [[Ploidy#Haploid and monoploid|haploid cell]] that fuses with another haploid cell during [[fertilization]] in [[organism]]s that [[Sexual reproduction|reproduce sexually]].<ref name="Encyclopedia Britannica">{{Cite web|title=gamete {{!}} Definition, Formation, Examples, & Facts|url=https://www.britannica.com/science/gamete|access-date=2020-10-20|website=Encyclopedia Britannica|language=en}}</ref> Gametes are an organism's '''reproductive cells''', also referred to as '''sex cells'''.<ref name="www.nature.com">{{Cite web|title=gamete / gametes {{!}} Learn Science at Scitable|url=https://www.nature.com/scitable/definition/gamete-gametes-311/|access-date=2020-10-20|website=www.nature.com}}</ref> The name gamete was introduced by the German cytologist [[Eduard Strasburger]] in 1878.<ref>{{Cite web |title=gamete {{!}} Etymology of gamete by etymonline |url=https://www.etymonline.com/word/gamete |access-date=2024-06-06 |website=www.etymonline.com |language=en}}</ref>

Gametes of both mating individuals can be the same size and shape, a condition known as [[isogamy]]. By contrast, in the majority of species, the gametes are of different sizes, a condition known as [[anisogamy]] or [[heterogamy]] that applies to humans and other mammals. The human ovum has approximately 100,000 times the volume of a single human sperm cell. The type of gamete an organism produces determines its [[sex]]<ref>{{Citation| vauthors = Cotner S, Wassenberg D |title=8.4 Sex: It's About the Gametes|url=https://open.lib.umn.edu/evolutionbiology/chapter/7-4-sex-its-about-the-gametes-2/|work=The Evolution and Biology of Sex|language=en|access-date=2020-10-20}}</ref> and sets the basis for the sexual roles and [[sexual selection]].<ref>{{Cite book| vauthors = Fusco G, Minelli A |url=https://books.google.com/books?id=AKGsDwAAQBAJ&q=the+biology+of+reproduction+define+male|title=The Biology of Reproduction |date=2019-10-10|publisher=Cambridge University Press|isbn=978-1-108-49985-9|pages=111–112|language=en}}</ref> In humans and other species that produce two [[Morphology (biology)|morphologically]] distinct types of gametes, and in which [[Gonochorism|each individual produces only one type]], a [[female]] is any individual that produces the larger type of gamete called an [[ovum]], and a [[male]] produces the smaller type, called a [[sperm]] cell or spermatozoon. Sperm cells are small and motile due to the presence of a tail-shaped structure, the [[flagellum]], that provides propulsion. In contrast, each egg cell or ovum is relatively large and non-motile.<ref name="www.nature.com" /> 

[[Oogenesis]], the process of female gamete formation in animals, involves [[meiosis]] (including [[Genetic recombination|meiotic recombination]]) of a diploid primary [[oocyte]] to produce a haploid [[Egg cell|ovum]]. [[Spermatogenesis]], the process of male gamete formation in animals, involves meiosis in a diploid primary [[spermatocyte]] to produce haploid [[spermatozoa]]. In animals, ova are produced in the ovaries of females and sperm develop in the testes of males. During fertilization, a spermatozoon and an ovum, each carrying half of the [[genetic information]] of an individual, unite to form a [[zygote]] that develops into a new [[diploid]] organism.<ref name="www.nature.com" />

== Evolution ==
{{Main|Evolution of sexual reproduction}}

It is generally accepted that [[isogamy]] is the ancestral state from which [[anisogamy]] and [[oogamy]] evolved, although its evolution has left no fossil records.<ref name="Pitnick-2008">{{cite book| vauthors = Pitnick SS, Hosken DJ, Birkhead TR |author-link3=Tim Birkhead |url=https://books.google.com/books?id=kctYNbO1fE0C&q=isogamy+in+multicellular+organisms&pg=PA44|title=Sperm Biology: An Evolutionary Perspective |publisher=Academic Press|year=2008|isbn=978-0-08-091987-4|pages=43–44}}</ref><ref>{{Cite book| vauthors = Awasthi AK |url=https://books.google.com/books?id=r0h1DwAAQBAJ&q=isogamy+generally+accepted&pg=PA363|title=Textbook of Algae|publisher=Vikas Publishing House|isbn=978-93-259-9022-7|pages=363|language=en}}</ref><ref>{{Cite book|vauthors=Dusenbery DB|url=https://books.google.com/books?id=QCrimQJu1RAC|title=Living at Micro Scale: The Unexpected Physics of Being Small|date=2009|publisher=Harvard University Press|isbn=978-0-674-03116-6|pages=309|language=en}}{{Dead link|date=May 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> There are almost invariably only two gamete types, all analyses showing that intermediate gamete sizes are eliminated due to selection.<ref>{{Cite book| vauthors = Stearns SC |url=https://books.google.com/books?id=1cQACAAAQBAJ|title=The Evolution of Sex and its Consequences|date=2013-11-21|publisher=Birkhäuser|isbn=978-3-0348-6273-8|pages=21, 81–82|language=en|author-link=Stephen C. Stearns}}</ref><ref name="Lehtonen">{{cite journal | vauthors = Lehtonen J, Parker GA | title = Gamete competition, gamete limitation, and the evolution of the two sexes | journal = Molecular Human Reproduction | volume = 20 | issue = 12 | pages = 1161–1168 | date = December 2014 | pmid = 25323972 | doi = 10.1093/molehr/gau068 | author-link2 = Geoff Parker | doi-access = free }}</ref> Since intermediate sized gametes do not have the same advantages as small or large ones,<ref>{{Cite book| vauthors = Campbell A |url=https://books.google.com/books?id=2FJoAgAAQBAJ&q=intermediate+gamete&pg=PA45|title=A Mind Of Her Own: The evolutionary psychology of women|date=2013-05-16|publisher=OUP Oxford|isbn=978-0-19-164701-7|pages=45|language=en}}</ref> they do worse than small ones in mobility and numbers, and worse than large ones in supply.<ref>{{cite journal | vauthors = Bachtrog D, Mank JE, Peichel CL, Kirkpatrick M, Otto SP, Ashman TL, Hahn MW, Kitano J, Mayrose I, Ming R, Perrin N, Ross L, Valenzuela N, Vamosi JC | title = Sex determination: why so many ways of doing it? | journal = PLOS Biology | volume = 12 | issue = 7 | pages = e1001899 | date = July 2014 | pmid = 24983465 | pmc = 4077654 | doi = 10.1371/journal.pbio.1001899 | s2cid = 3741933 | doi-access = free | author-link2 = Judith Mank }}</ref>

==Differences between gametes and somatic cells==
In contrast to a gamete, which has only one set of chromosomes, a diploid [[somatic cell]] has two sets of [[homologous chromosome]]s, one of which is a copy of the [[chromosome]] set from the sperm and one a copy of the chromosome set from the egg cell. [[Genetic recombination|Recombination of the genes]] during meiosis ensures that the chromosomes of gametes are not exact duplicates of either of the sets of chromosomes carried in the parental diploid chromosomes but a mixture of the two.<ref>{{Cite web|title=Mitosis, Meiosis, and Inheritance {{!}} Learn Science at Scitable|url=https://www.nature.com/scitable/topicpage/mitosis-meiosis-and-inheritance-476/|access-date=2021-03-01|website=www.nature.com|language=en}} Consequently, the cells of the offspring have genes potentially capable of expressing some of the characteristics of both the father and the mother, subject to whether they are [[Dominance (genetics)|dominant or recessive]]. </ref>
[[File:Sperm-egg.jpg|thumb|263x263px|A human spermatozoon fusing with a human ovum. The spermatozoon is approximately 100,000 times smaller in size than the human ovum.]]

==Artificial gametes==
Artificial gametes, also known as in vitro derived gametes (IVD), stem cell-derived gametes (SCDGs), and in vitro generated gametes (IVG), are gametes derived from [[stem cell]]s. The use of such artificial gametes would "necessarily require [[In vitro fertilisation|IVF]] techniques".<ref name="med"/> Research shows that artificial gametes may be a reproductive technique for same-sex male couples, although a [[surrogate mother]] would still be required for the gestation period.<ref name="med">{{cite journal | vauthors = Newson AJ, Smajdor AC | title = Artificial gametes: new paths to parenthood? | journal = Journal of Medical Ethics | volume = 31 | issue = 3 | pages = 184–186 | date = March 2005 | pmid = 15738444 | pmc = 1734101 | doi = 10.1136/jme.2003.004986 | quote = Pregnancies brought about by means of artificial gametes would necessarily require [[In vitro fertilisation|IVF]] techniques }}</ref> Women who have passed [[menopause]] may be able to produce eggs and bear genetically related children with artificial gametes.<ref name="med"/> Robert Sparrow wrote, in the [[Journal of Medical Ethics]], that embryos derived from artificial gametes could be used to derive new gametes and this process could be repeated to create multiple human generations in the laboratory.<ref name="sparrow">{{cite journal | vauthors = Sparrow R | title = In vitro eugenics | journal = Journal of Medical Ethics | volume = 40 | issue = 11 | pages = 725–731 | date = November 2014 | pmid = 23557913 | doi = 10.1136/medethics-2012-101200 | s2cid = 959092 | url = https://research.monash.edu/en/publications/72686ba6-5d7d-49ca-88a8-0fa8e1b83960 }}</ref> This technique could be used to create [[cell culture|cell lines]] for medical applications and for studying the heredity of [[genetic disorder]]s.<ref name="sparrow"/> Additionally, this technique could be used for [[human enhancement]] by [[selective breeding|selectively breeding]] for a desired genome or by using [[recombinant DNA]] technology to create enhancements that have not arisen in nature.<ref name="sparrow"/>

==Plants==
[[Plants]] that reproduce sexually also produce gametes. However, since plants have a life cycle involving [[Alternation of generations|alternation of diploid and haploid generations]] some differences from animal life cycles exist. Plants use [[meiosis]] to produce spores that develop into [[Multicellular organism|multicellular]] haploid [[gametophyte]]s which produce gametes by mitosis. In animals there is no corresponding multicellular haploid phase. The sperm of plants that reproduce using spores are formed by mitosis in an organ of the gametophyte known as the [[antheridium]] and the egg cells by mitosis in a flask-shaped organ called the [[archegonium]].<ref name=Sporne2022>{{cite book | vauthors = Sporne KR |date=2022 |title=The morphology of Pteridophytes; the structure of ferns and allied plants |publisher=Legare Street Press |isbn=978-1015505667 }}</ref> Plant sperm cells are their only motile cells, often described as flagellate, but more correctly as ciliate.<ref name=Wolniak2000>{{cite journal | vauthors = Wolniak SM, Klink VP, Hart PE, Tsai CW | title = Control of development and motility in the spermatozoids of lower plants | journal = Gravitational and Space Biology Bulletin | volume = 13 | issue = 2 | pages = 85–93 | date = June 2000 | pmid = 11543285 }}</ref> Bryophytes have 2 flagella, horsetails have up to 200 and the mature spermatozoa of the [[cycad]] ''Zamia pumila'' has up to 50,000 flagella.<ref name=Norstog1986>{{cite journal | vauthors = Norstog KJ |title=The blepharoplast of ''Zamia pumila'' L. |journal=Botanical Gazette |date=1986 |volume=147 |issue=1 |pages=40–46 |doi=10.1086/337566 |s2cid=85257438 }}</ref> Cycads and ''Ginkgo biloba'' are the only gymnosperms with motile sperm.<ref name=Wolniak2000/> In the [[flowering plant]]s, the female gametophyte is produced inside the [[ovule]] within the [[Ovary (botany)|ovary]] of the flower. When mature, the haploid gametophyte produces female gametes which are ready for fertilization. The male gametophyte is produced inside a [[pollen]] grain within the [[anther]] and is non-motile, but can be distributed by wind, water or animal vectors. When a pollen grain lands on a mature [[stigma (botany)|stigma]] of a flower it germinates to form a [[pollen tube]] that grows down the style into the ovary of the flower and then into the ovule. The pollen then produces non-motile sperm nuclei by mitosis that are transported down the pollen tube to the ovule where they are released for fertilization of the egg cell.

== See also ==
* [[Coenogamete]]

==References==
{{Reflist}}

{{Reproductive physiology}}
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[[Category:Classical genetics]]
[[Category:Germ cells]]
[[Category:Reproductive system]]