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{{Short description|Procreative biological processes of humanity}}
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{{Sex (biology) sidebar}}
'''Human reproduction''' is [[sexual reproduction]] that results in [[human fertilization]] to produce a human offspring. It typically<!-- NOTE: "Typically" is here because, as is clear from the rest of the lead and lower in the article, human reproduction can also be achieved via artificial insemination and assisted reproductive technology. Also, human cloning can theoretically be done, see [[animal cloning]].--> involves [[sexual intercourse]] between a [[sexual maturity|sexually mature]] human [[male]] and [[female]].<ref name=":1">{{Citation |last=Jones |first=Richard E. |title=The Male Reproductive System |date=1991 |work=Human Reproductive Biology |pages=72–93 |publisher=Elsevier |doi=10.1016/b978-0-12-389770-1.50008-1 |isbn=9780123897701 }}</ref> During sexual intercourse, the interaction between the [[male reproductive system|male]] and [[female reproductive system]]s results in fertilization of the [[ovum]] by the [[sperm]] to form a zygote.<ref name=":1" /> While normal cells contain 46 [[chromosome]]s (23 pairs), gamete cells only contain 23 single chromosomes, and it is when these two cells merge into one [[zygote]] cell that [[genetic recombination]] occurs and the new zygote contains 23 chromosomes from each parent, giving it 46 chromosomes (23 pairs).<ref name=":2">{{Cite web |title=Gametogenesis – an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/medicine-and-dentistry/gametogenesis |access-date=2022-09-12 |website=sciencedirect.com}}</ref> The zygote then undergoes a defined development process that is known as human embryogenesis, and this starts the typical 9-month [[gestation period]] that is followed by [[childbirth]]. The fertilization of the ovum may be achieved by [[artificial insemination]] methods, which do not involve sexual intercourse.<ref name=":3">{{Cite journal |last1=Ombelet |first1=W. |last2=Van Robays |first2=J. |date=2015 |title=Artificial insemination history: hurdles and milestones |journal=Facts, Views & Vision in ObGyn |volume=7 |issue=2 |pages=137–143 |issn=2032-0418 |pmc=4498171 |pmid=26175891 }}</ref> [[Assisted reproductive technology]] also exists.
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===Male reproductive system ===
{{Further|Male reproductive system}}
The male reproductive system contains two main divisions: the [[testicle]]s where [[sperm]] are produced, and the [[human penis|penis]] where [[semen]] is [[ejaculated]] through the [[urethra]]. In humans, both of these organs are outside the [[abdominal cavity]]. Having the testicles outside the abdomen facilitates temperature regulation of the sperm, which require specific temperatures to survive about 2-3 °C less than the normal body temperature i.e. 37 °C. In particular, the extraperitoneal location of the testicles may result in a 2-fold reduction in the heat-induced contribution to the spontaneous mutation rate in male germinal tissues compared to tissues at 37 °C.<ref>{{cite journal | author = Baltz RH, Bingham PM, Drake JW | year = 1976 | title = Heat mutagenesis in bacteriophage T4: The transition pathway | journal = Proc. Natl. Acad. Sci. USA | volume = 73 | issue = 4| pages = 1269–1273 | pmid = 4797 | pmc = 430244 | doi = 10.1073/pnas.73.4.1269 | bibcode = 1976PNAS...73.1269B | doi-access = free }}</ref> If the testicles remain too close to the body, it is likely that the increase in temperature will harm the spermatozoa formation, making conception more difficult. This is why the testes are carried in an external [[scrotum]] rather than within the abdomen; they normally remain slightly cooler than body temperature, facilitating sperm production.
Male [[germ cell]]s produced in the testes are able to perform special [[DNA repair]] processes during meiosis that act 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> Two of these DNA repair processes are [[homologous recombination]]al repair and [[non-homologous end joining]].<ref name = Garcia-Rodriguez2018/>
=== Female reproductive system ===
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The ova, which are the female sex cells, are much larger than the spermatozoon and are normally formed within the [[Ovary|ovaries]] of the female fetus before birth. They are mostly fixed in location within the ovary until their transit to the uterus, and contain nutrients for the later [[zygote]] and [[embryo]]. Over a regular interval known as the [[menstrual cycle]], in response to hormonal signals, a process of [[oogenesis]] matures one ovum which is released and sent down the fallopian tube. If not fertilized, this egg is flushed out of the system through [[menstruation]].
[[Oocyte]]s (female germ cells) 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 |url=}}</ref> This capability allows the maintenance of [[genome]] integrity and protection of the health of offspring.<ref name = Stringer2020/>
== Process of fertilization ==
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