Editing Zygote

{{Short description|Diploid eukaryotic cell formed by fertilization between two gametes}}
{{Other uses}}
{{Redirect|Fertilized egg|the food product|Balut (food)}}
{{Infobox embryology
| Name          = Zygote
| Image         = Zygote1.jpg
| Caption       = Zygote formation: [[egg cell]] after [[fertilization]] with a [[sperm]]. The male and female [[pronuclei]] are converging, but the genetic material is not yet united.
| Image2        =
| Caption2      =
| System        =
| CarnegieStage =
| Days          = 0
| Precursor     = [[Gamete]]s
| GivesRiseTo   = [[Blastomere]]s
}}
{{Human growth and development}}

A '''zygote''' ({{IPAc-en|ˈ|z|aɪ|ˌ|g|oʊ|t|audio=LL-Q1860 (eng)-Naomi Persephone Amethyst (NaomiAmethyst)-zygote.wav}}; {{etymology|grc|''ζυγωτός'' (zygōtós)|joined, yoked}}, {{etymology||''ζυγοῦν'' (zygoun)|to join, to yoke}})<ref>{{cite web |url=http://www.etymonline.com/index.php?term=zygote |title=English etymology of zygote |work=etymonline.com |url-status=live |archive-url=https://web.archive.org/web/20170330174125/http://www.etymonline.com/index.php?term=zygote |archive-date=2017-03-30 }}</ref> is a [[eukaryote|eukaryotic]] [[cell (biology)|cell]] formed by a [[fertilization]] event between two [[gamete]]s. The zygote's [[genome]] is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. The sexual fusion of haploid cells is called [[karyogamy]], the result of which is the formation of a [[Ploidy#Haploid and monoploid|diploid cell]] called the zygote or zygospore.

==History==

German zoologists [[Oscar Hertwig|Oscar]] and [[Richard Hertwig]] made some of the first discoveries on animal zygote formation in the late 19th century.{{cn|date=March 2025}}

==In multicellular organisms==

The zygote is the earliest developmental stage. In humans and most other [[Anisogamy|anisogamous]] organisms, a zygote is formed when an [[egg cell]] and [[sperm|sperm cell]] come together to create a new unique organism.{{cn|date=March 2025}}

The formation of a [[cell potency|totipotent]] zygote with the potential to produce a whole organism depends on [[epigenetics|epigenetic]] reprogramming.  [[DNA demethylation]] of the paternal [[genome]] in the zygote appears to be an important part of epigenetic reprogramming.<ref name="pmid27916276">{{cite journal |vauthors=Ladstätter S, Tachibana-Konwalski K |title=A Surveillance Mechanism Ensures Repair of DNA Lesions during Zygotic Reprogramming |journal=Cell |volume=167 |issue=7 |pages=1774–1787.e13 |date=December 2016 |pmid=27916276 |pmc=5161750 |doi=10.1016/j.cell.2016.11.009 }}</ref>  In the paternal genome of the mouse, demethylation of DNA, particularly at sites of methylated cytosines, is likely a key process in establishing totipotency.  Demethylation involves the processes of [[base excision repair]] and possibly other DNA-repair–based mechanisms.<ref name="pmid27916276" />

=== Humans ===
{{Main|Development of the human body|Human fertilization}}
[[File: Egg cell fertilization - Zygote.png|thumb| ]]
In [[human fertilization]], a released ovum (a haploid secondary [[oocyte]] with replicate chromosome copies) and a haploid [[sperm]] cell ([[male]] gamete) combine to form a single [[diploid cell]] called the zygote. Once the single sperm fuses with the oocyte, the latter completes the division of the second [[meiosis]] forming a haploid daughter with only 23 chromosomes, almost all of the cytoplasm, and the male [[pronucleus]].  The other product of meiosis is the second polar body with only chromosomes but no ability to replicate or survive. In the fertilized daughter, DNA is then replicated in the two separate pronuclei derived from the sperm and ovum, making the zygote's chromosome number temporarily [[Ploidy|4n diploid]]. After approximately 30 hours from the time of fertilization, a fusion of the pronuclei and immediate mitotic division produce two [[Ploidy|2n diploid]] daughter cells called [[blastomere]]s.<ref>[http://www.britannica.com/EBchecked/topic/69084/blastomere Blastomere  Encyclopædia Britannica] {{webarchive|url=https://web.archive.org/web/20130928075445/http://www.britannica.com/EBchecked/topic/69084/blastomere |date=2013-09-28 }}. Encyclopædia Britannica Online. Encyclopædia Britannica Inc., 2012. Web. 06 Feb. 2012.</ref>
Between the stages of fertilization and [[Implantation (human embryo)|implantation]], the developing [[embryo]] is sometimes termed as a ''preimplantation-[[conceptus]]''. This stage has also been referred to as the '''pre-embryo''' in legal discourses including relevance to the use of embryonic stem cells.<ref>{{cite journal|last1=Condic|first1=Maureen L.|title=Totipotency: What It Is And What It Is Not|journal=Stem Cells and Development|date=14 April 2014|pmc=3991987|pmid=24368070|doi=10.1089/scd.2013.0364|volume=23|issue=8|pages=796–812}}</ref> In the US the National Institutes of Health has determined that the traditional classification of pre-implantation embryo is still correct.<ref>{{cite web |url=http://ospp.od.nih.gov/pdf/Volume1_revised.pdf |title=Report of the Human Embryo Research Panel |access-date=2009-02-17 |url-status=dead |archive-url=https://web.archive.org/web/20090130185105/http://ospp.od.nih.gov/pdf/VOLUME1_REVISED.PDF |archive-date=2009-01-30 }}</ref>

After fertilization, the conceptus travels down the [[fallopian tube]] towards the [[uterus]] while continuing to [[Mitosis|divide]]<ref>O'Reilly, Deirdre. "[https://www.nlm.nih.gov/medlineplus/ency/article/002398.htm Fetal development] {{webarchive|url=https://web.archive.org/web/20111027150119/http://www.nlm.nih.gov/medlineplus/ency/article/002398.htm |date=2011-10-27 }}". ''[[MedlinePlus|MedlinePlus Medical Encyclopedia]]'' (2007-10-19). Retrieved 2009-02-15.</ref> without actually increasing in size, in a process called [[cleavage (embryo)|cleavage]].<ref>Klossner, N. Jayne and Hatfield, Nancy. ''[https://books.google.com/books?id=rAOTF7g6tbgC&dq=zygote+cleavage+blastocyst&pg=PA107 Introductory Maternity & Pediatric Nursing],'' p. 107 ([[Lippincott Williams & Wilkins]], 2006).</ref> After four divisions, the conceptus consists of 16 blastomeres, and it is known as the [[morula]].<ref>Neas, John F. [http://cwx.prenhall.com/bookbind/pubbooks/martini10/chapter28/custom3/deluxe-content.html "Human Development"] {{webarchive |url=https://web.archive.org/web/20110722153852/http://cwx.prenhall.com/bookbind/pubbooks/martini10/chapter28/custom3/deluxe-content.html |date=July 22, 2011 }}. ''Embryology Atlas''</ref> Through the processes of compaction, cell division, and blastulation, the conceptus takes the form of the [[blastocyst]] by the fifth day of development, just as it approaches the site of implantation.<ref>Blackburn, Susan. ''[https://books.google.com/books?id=2y6zOSQcn14C&dq=zygote&pg=PA80 Maternal, Fetal, & Neonatal Physiology],'' p. 80 (Elsevier Health Sciences 2007).</ref> When the blastocyst hatches from the [[zona pellucida]], it can implant in the endometrial lining of the uterus and begin the [[gastrulation]] stage of embryonic development.{{cn|date=March 2025}}

The human zygote has been genetically edited in experiments designed to cure inherited diseases.<ref>{{Cite web|url=https://www.sciencenews.org/article/editing-human-germline-cells-sparks-ethics-debate|archive-url=https://web.archive.org/web/20150518191952/https://www.sciencenews.org/article/editing-human-germline-cells-sparks-ethics-debate|url-status=dead|title=Editing human germline cells sparks ethics debate|date=May 6, 2015|archive-date=May 18, 2015|access-date=May 17, 2020}}</ref>

=== Fungi ===

In fungi, this cell may then enter meiosis or mitosis depending on the life cycle of the species.{{cn|date=March 2024}}

=== Plants ===

In plants, the zygote may be [[Ploidy#Polyploidy|polyploid]] if fertilization occurs between meiotically unreduced gametes.{{cn|date=March 2025}}

In [[embryophyte|land plants]], the zygote is formed within a chamber called the [[archegonium]].  In seedless plants, the archegonium is usually flask-shaped, with a long hollow neck through which the sperm cell enters. As the zygote divides and grows, it does so inside the archegonium.{{cn|date=March 2024}}

== In single-celled organisms ==

The zygote can divide asexually by [[mitosis]] to produce identical offspring.{{cn|date=March 2024}}

A ''[[Chlamydomonas]]'' zygote contains [[chloroplast DNA]] (cpDNA) from both parents; such cells are generally rare, since normally cpDNA is inherited uniparentally from the mt+ mating type parent. These rare biparental zygotes allowed mapping of chloroplast genes by recombination.{{cn|date=March 2024}}

==See also==
* [[Breastfeeding and fertility]]
* [[Fertilization]]
* [[Proembryo]]

==References==
{{Reflist}}
{{Wiktionary}}

{{s-start}}
{{s-bef|before=[[Oocyte]] + [[Sperm]]}}
{{s-ttl|title=[[Stages of human development]]|years=Zygote}}
{{s-aft|after=[[Embryo]]}}
{{S-end}}

{{Embryology}}
{{Eggs}}
{{Authority control}}

[[Category:Developmental biology]]
[[Category:Human pregnancy]]