Editing Reproduction (section)

==Sexual==
{{Main|Sexual reproduction}}
{{See also|Human reproduction}}
{{More citations needed section|date=August 2021}}
{{multiple image|perrow=1|image1=Hoverflies mating midair.jpg|caption1=[[Hoverfly|Hoverflies]] mate in midair flight|image2=Korean wolves mating (cropped).jpg|caption2=[[Bird]]s, [[reptile]]s, and [[Mammalian reproduction|mammals reproduce]] by [[internal fertilization]]. Male mammals [[ejaculation|ejaculate]] [[semen]] through the [[penis]] into the [[vagina]] during [[copulation (zoology)|copulation]].<ref name="Hyman1992">{{cite book |author=Libbie Henrietta Hyman |url=https://books.google.com/books?id=VKlWjdOkiMwC&pg=PA583 |title=Hyman's Comparative Vertebrate Anatomy |date=15 September 1992 |publisher=University of Chicago Press |isbn=978-0-226-87013-7 |pages=583–}}</ref><ref name=":0">{{Cite book |last=Birkhead |first=Tim |url=https://books.google.com/books?id=3i4Q8SvohfEC&q=insemination |title=Promiscuity: An Evolutionary History of Sperm Competition |date=2000 |publisher=Harvard University Press |isbn=978-0-674-00666-9 |language=en}}</ref>
}}
Sexual reproduction is a [[biological process]] that creates a new [[organism]] by combining the [[Genetics|genetic]] material of two organisms in a process that starts with [[meiosis]], a specialized type of [[cell division]]. Each of two parent organisms contributes half of the offspring's genetic makeup by creating [[haploid]] [[gametes]].<ref>{{Citation|last1=Griswold|first1=M. D.|title=Meiosis|date=2013-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780123749840009165|encyclopedia=Brenner's Encyclopedia of Genetics (Second Edition)|pages=338–341|editor-last=Maloy|editor-first=Stanley|place=San Diego|publisher=Academic Press|language=en|isbn=978-0-08-096156-9|access-date=2020-10-05|last2=Hunt|first2=P. A.|editor2-last=Hughes|editor2-first=Kelly|archive-date=2021-04-20|archive-url=https://web.archive.org/web/20210420024023/https://www.sciencedirect.com/science/article/pii/B9780123749840009165|url-status=live}}</ref> Most organisms form two different types of gametes. In these '''''anisogamous''''' species, the two sexes are referred to as male (producing [[sperm]] or microspores) and female (producing [[ovum|ova]] or megaspores).<ref name="Kumar-201922">{{Cite encyclopedia|entry=Anisogamy|encyclopedia=Encyclopedia of Animal Cognition and Behavior|publisher=Springer International Publishing|place=Cham |date=2019|pages=1–5|doi=10.1007/978-3-319-47829-6_340-1|isbn=978-3-319-47829-6 |vauthors=Kumar R, Meena M, Swapnil P|title=Anisogamy |veditors=Vonk J, Shackelford T}}</ref> In '''''isogamous species''''', the gametes are similar or identical in form ([[isogamete]]s), but may have separable properties and then may be given other different names (see [[isogamy]]).<ref>{{Cite journal|last1=Lehtonen|first1=Jussi|last2=Kokko|first2=Hanna|last3=Parker|first3=Geoff A.|date=2016-10-19|title=What do isogamous organisms teach us about sex and the two sexes?|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|volume=371|issue=1706|doi=10.1098/rstb.2015.0532|issn=0962-8436|pmc=5031617|pmid=27619696}}</ref> Because both gametes look alike, they generally cannot be classified as male or female. For example, in the green alga, ''Chlamydomonas reinhardtii'', there are so-called "plus" and "minus" gametes. A few types of organisms, such as many fungi and the [[ciliate]] ''Paramecium aurelia'',<ref>{{cite journal |author=T.M. Sonneborn |title=Mating Types in Paramecium Aurelia: Diverse Conditions for Mating in Different Stocks; Occurrence, Number and Interrelations of the Types |journal=Proceedings of the American Philosophical Society |volume=79 |issue=3 |pages=411–434 |publisher=American Philosophical Society |jstor=984858 |year=1938}}</ref> have more than two  "sexes", called [[mating type]]s.
Most animals (including humans) and plants reproduce sexually. Sexually reproducing organisms have different sets of genes for every trait (called [[alleles]]). Offspring inherit one allele for each trait from each parent. Thus, offspring have a combination of the parents' genes. It is believed that "the masking of deleterious alleles favors the evolution of a dominant diploid phase in organisms that alternate between haploid and diploid phases" where recombination occurs freely.<ref>{{cite journal |last1=Otto |first1=S.P. |last2=Goldstein |first2=D.B. |year=1992 |title=Recombination and the Evolution of Diploidy |journal=[[Genetics (journal)|Genetics]] |volume=131 |issue=3 |pages=745–751 |doi=10.1093/genetics/131.3.745 |pmid=1628815 |pmc=1205045}}</ref><ref>{{cite book |last1=Bernstein |first1=H. |last2=Hopf |first2=F.A. |last3=Michod |first3=R.E. |chapter=The Molecular Basis of the Evolution of Sex |year=1987 |title=Molecular Genetics of Development |series=Advances in Genetics |volume=24 |pages=323–370 |pmid=3324702 |doi=10.1016/s0065-2660(08)60012-7 |isbn=978-0120176243}}</ref>

[[Bryophyte]]s reproduce sexually, but the larger and commonly-seen organisms are [[haploid]] and produce [[gametes]]. The gametes fuse to form a [[zygote]] which develops into a [[sporangium]], which in turn produces haploid spores. The [[diploid]] stage is relatively small and short-lived compared to the haploid stage, i.e. ''haploid dominance''. The advantage of diploidy, heterosis, only exists in the diploid life generation. Bryophytes retain sexual reproduction despite the fact that the haploid stage does not benefit from heterosis. This may be an indication that the sexual reproduction has advantages other than heterosis, such as [[genetic recombination]] between members of the species, allowing the expression of a wider range of traits and thus making the population more able to survive environmental variation.<ref>{{cite journal |last1=Haig |first1=David |title=Living together and living apart: the sexual lives of bryophytes |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |date=19 October 2016 |volume=371 |issue=1706 |pages=20150535 |doi=10.1098/rstb.2015.0535 |pmid=27619699 |pmc=5031620 }}</ref>

===Allogamy===
{{Main|Allogamy}}

Allogamy is the fertilization of flowers through cross-pollination, this occurs when a flower's ovum is fertilized by spermatozoa from the pollen of a different plant's flower.<ref>{{cite web |title=Allogamy |url=https://www.biologyonline.com/dictionary/allogamy |website=Biology Online |access-date=20 August 2022 |date=7 October 2019 |archive-date=25 September 2021 |archive-url=https://web.archive.org/web/20210925025751/https://www.biologyonline.com/dictionary/allogamy |url-status=live }}</ref><ref name="plant systematics">{{cite book |last1=Simpson |first1=Michael G. |title=Plant systematics |date=2019 |publisher=Academic Press |location=Burlington, MA |isbn=978-0128126288 |pages=595–606 |edition=3rd |chapter-url=https://www.sciencedirect.com/science/article/pii/B9780128126288500134 |chapter=13 – Plant Reproductive Biology |access-date=2022-08-20 |archive-date=2022-08-20 |archive-url=https://web.archive.org/web/20220820183122/https://www.sciencedirect.com/science/article/pii/B9780128126288500134 |url-status=live }}</ref> Pollen may be transferred through [[pollinator|pollen vectors]] or abiotic carriers such as wind. Fertilization begins when the pollen is brought to a female gamete through the pollen tube. Allogamy is also known as cross fertilization, in contrast to autogamy or geitonogamy which are methods of self-fertilization.

===Autogamy===
{{main|Autogamy}}

Self-[[fertilization]], also known as autogamy, occurs in [[hermaphrodite|hermaphroditic]] organisms where the two [[gamete]]s fused in fertilization come from the same individual, e.g., many [[vascular plants]], some [[foraminifera]]ns, some [[ciliate]]s.<ref name="plant systematics" /> The term "autogamy" is sometimes substituted for autogamous pollination (not necessarily leading to successful fertilization) and describes [[self-pollination]] within the same flower, distinguished from [[geitonogamy|geitonogamous pollination]], transfer of pollen to a different flower on the same [[flowering plant]],<ref>{{cite journal |author=Eckert, C.G. |year=2000 |title=Contributions of autogamy and geitonogamy to self-fertilization in a mass-flowering, clonal plant |journal=Ecology |volume=81 |issue=2 |pages=532–542 |doi=10.1890/0012-9658(2000)081[0532:coaagt]2.0.co;2}}</ref> or within a single [[monoecious]] [[gymnosperm]] plant.

===Mitosis and meiosis===
[[Mitosis]] and [[meiosis]] are types of [[cell division]]. Mitosis occurs in [[somatic cells]], while meiosis occurs in [[gametes]].

'''Mitosis'''
The resultant number of cells in mitosis is twice the number of original cells. The number of [[chromosomes]] in the offspring cells is the same as that of the parent cell.
{{Clear}}<!-- Unsourced image removed: [[File:mitosis.jpg|center]] -->
'''Meiosis'''
The resultant number of cells is four times the number of original cells. This results in cells with half the number of [[chromosomes]] present in the parent cell. A [[diploid]] cell duplicates itself, then undergoes two divisions ([[tetraploid]] to diploid to haploid), in the process forming four [[haploid]] cells. This process occurs in two phases, meiosis I and meiosis II.
{{Clear}}<!-- Unsourced image removed: [[File:meiosis.jpg|center]] -->

===Gametogenesis===

Animals, including mammals, produce gametes (sperm and egg) by means of  [[Origin and function of meiosis|meiosis]] in gonads (testicles in males and ovaries in females).  Sperm are produced by  [[spermatogenesis]] and eggs are produced by [[oogenesis]].  During gametogenesis in mammals numerous genes encoding proteins that participate in DNA repair mechanisms exhibit enhanced or specialized expression.<ref name="pmid11226027">{{cite journal |vauthors=Baarends WM, van der Laan R, Grootegoed JA |title=DNA repair mechanisms and gametogenesis |journal=Reproduction |volume=121 |issue=1 |pages=31–9 |year=2001 |pmid=11226027 |doi= 10.1530/reprod/121.1.31|doi-access=free |hdl=1765/9599 |hdl-access=free }}</ref>  Male [[germ cell]]s produced in the testes of animals are capable of special [[DNA repair]] processes that function during meiosis to repair DNA damages and to maintain the integrity of the [[genome]]s that are to be passed on to progeny.<ref name = Garcia-Rodriguez2018>{{cite journal |vauthors=García-Rodríguez A, Gosálvez J, Agarwal A, Roy R, Johnston S |title=DNA Damage and Repair in Human Reproductive Cells |journal=Int J Mol Sci |volume=20 |issue=1 |date=December 2018 |page=31 |pmid=30577615 |doi=10.3390/ijms20010031 |doi-access=free |pmc=6337641 |url=}}</ref>  Such DNA repair processes include [[homologous recombination]]al repair as well as [[non-homologous end joining]].<ref name = Garcia-Rodriguez2018/>  [[Oocyte]]s located in the [[folliculogenesis|primordial follicle]] of the ovary are in a non-growing [[prophase]] arrested state, but are able to undergo highly efficient [[homologous recombination]]al repair of [[DNA damage (naturally occurring)|DNA damages]] including double-strand breaks.<ref name = Stringer2020>{{cite journal |vauthors=Stringer JM, Winship A, Zerafa N, Wakefield M, Hutt K |title=Oocytes can efficiently repair DNA double-strand breaks to restore genetic integrity and protect offspring health |journal=Proc Natl Acad Sci U S A |volume=117 |issue=21 |pages=11513–11522 |date=May 2020 |pmid=32381741 |pmc=7260990 |doi=10.1073/pnas.2001124117 |doi-access=free |bibcode=2020PNAS..11711513S |url=}}</ref>  These repair processes allow the integrity of the [[genome]] to be maintained and offspring health to be protected.<ref name = Stringer2020/>