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{{BioPsy}}
  
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A '''zygote''' ([[Greek language|Greek]]: ''ζυγωτόν'') is a [[cell (biology)|cell]] that is the result of [[fertilization]]. That is, two [[ploidy|haploid]] cells—usually (but not always) an [[ovum]] from a [[female]] and a [[sperm]] cell from a [[male]]—merge into a single [[ploidy|diploid]] cell called the ''zygote'' (or ''zygocyte'').
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A '''zygote''' (from [[Greek language|Greek]] ζυγωτός ''zygōtos'' "joined" or "yoked", from ζυγοῦν ''zygoun'' "to join" or "to yoke"),<ref>{{cite web| url=http://www.myetymology.com/english/zygote.html |title=English etymology of zygote |work=myetymology.com}}</ref> or '''zygocyte''', is the initial [[cell (biology)|cell]] formed when a new [[organism]] is produced by means of [[sexual reproduction]]. A zygote is synthesized from the union of two [[gamete]]s, and constitutes the first stage in a unique organism's [[developmental biology|development]]. Zygotes are usually produced by a [[fertilization]] event between two [[ploidy|haploid]] cells — an [[ovum]] from a [[female]] and a [[sperm]] cell from a [[male]] — which combine to form the single [[ploidy|diploid]] cell. Such zygotes contain [[DNA]] derived from both the mother and the father, and this provides all the genetic information necessary to form a new individual. The term ''zygote'' is also used more loosely to refer to the group of cells formed by the first few cell divisions, although this is properly referred to as a [[morula]].
   
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In [[mammal]]ian reproduction, after fertilization has taken place the zygote travels down the [[fallopian tube]], while [[cell division|dividing to form more cells]]<ref>O’Reilly, Deirdre. [http://www.nlm.nih.gov/medlineplus/ency/article/002398.htm “Fetal development,”] ''[[MedlinePlus|MedlinePlus Medical Encyclopedia]]'' (2007-10-19). Retrieved 2009-02-15.</ref> without the zygote actually increasing in size. This cell division is [[mitosis|mitotic]], and is known as ''[[cleavage (embryo)|cleavage]]''.<ref>Klossner, N. Jayne and Hatfield, Nancy. ''[http://books.google.com/books?id=rAOTF7g6tbgC&pg=PA107&dq=zygote+cleavage+blastocyst&as_brr=3&ei=mJaYSbj2CZjEM-Hc9KQJ Introductory Maternity & Pediatric Nursing,]'' p. 107 ([[Lippincott Williams & Wilkins]], 2006).</ref> All mammals go through the zygote stage of life. Zygotes eventually develop into an [[embryo]], and then a [[fetus]]. A human zygote exists for about four days, and becomes a [[blastocyst]] on the fifth day.<ref>Blackburn, Susan. ''[http://books.google.com/books?id=2y6zOSQcn14C&pg=PA77&dq=zygote&num=100&as_brr=3&ei=lwCTSf_4EoTOlQT4zdClAg#PPA80,M1 Maternal, Fetal, & Neonatal Physiology,]'' p. 80 (Elsevier Health Sciences 2007).</ref>
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Animal zygotes undergo [[mitosis|mitotic]] [[cell division]]s to become an [[embryo]]. Other organisms may undergo [[meiosis|meiotic]] cell division at this time (for more information refer to [[biological life cycle]]s).
 
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==Twins==
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[[Twin]]s and [[multiple birth]]s can be monozygotic (identical) or dizygotic (fraternal). Dizygotic twins arise from one or several — strictly, two — fertilization events. [[Polyspermy|Polyspermic]] zygotes in mice have been manipulated so as to remove one of the two male [[pronucleus|pronuclei]] and made to survive birth.<ref>{{cite web| url=http://www.ncbi.nlm.nih.gov/pubmed/8671222| title=Birth of normal mice after removal of the supernumerary male pronucleus from polyspermic zygotes all zygotes are halpliods. |work=[[National Center for Biotechnology Information]]}}</ref>
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[[Conjoined twins]], sometimes called "Siamese twins", occur once in every two hundred identical twin pregnancies and are always identical. Actual numbers for conjoined births vary from 1 in 20,000 to 1 in 100,000 pregnancies; 40–60% are [[stillbirth|stillborn]], with many others dying within the first few days after birth. About 70% of conjoined twins are female, the reason for which is unknown.
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The first successful separation of conjoined twins was performed in [[Basle]], Switzerland in 1689 on twin girls born joined by a [[ligament]] at the [[sternum]] (xiphopagus). The first to be successfully separated in modern times are generally believed to be Catherine and Caroline Mouton of Louisiana, born joined at the lower back (pygopagus) and separated in 1953 at eight days of age. Both survived the operation. Separation has been attempted on almost all conjoined twins born since the 1950s, with varying results.
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==In other species==
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A '''biparental zygote''' is a [[Chlamydomonas]] (a kind of [[algae]]) zygote that contains [[chloroplast]] DNA ([[cpDNA]]) from both parents.
   
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[[Twin]]s and [[multiple birth]]s can be monozygotic (identical) or dizygotic (fraternal).
  
   
 
==See also==
  
==See also==
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* [[Biological life cycle]]
 
* [[Embryo]]
  
* [[Embryo]]
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* [[Pregnancy]]
  
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* [[Zygote intrafallopian transfer]]
  
 
* [[Embryogenesis]]
  
* [[Embryogenesis]]
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* [[Biological life cycle]]
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* [[Pregnancy]]
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* [[Sexual reproduction]]
 
* [[Stephen Ruiz]]
  
* [[Stephen Ruiz]]
   
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==References==
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{{succession box|title=[[Stages of human development]] |before=[[Oocyte]]<br />[[Sperm]]|after=[[Embryo]]|years=Zygote}}
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{{Embryology}}
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[[Category:Developmental biology]]
  
[[Category:Developmental biology]]
 
[[Category:Reproductive system]]
  
[[Category:Reproductive system]]
   
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Revision as of 12:23, 1 April 2010

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A zygote (from Greek ζυγωτός zygōtos "joined" or "yoked", from ζυγοῦν zygoun "to join" or "to yoke"),[1] or zygocyte, is the initial cell formed when a new organism is produced by means of sexual reproduction. A zygote is synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development. Zygotes are usually produced by a fertilization event between two haploid cells — an ovum from a female and a sperm cell from a male — which combine to form the single diploid cell. Such zygotes contain DNA derived from both the mother and the father, and this provides all the genetic information necessary to form a new individual. The term zygote is also used more loosely to refer to the group of cells formed by the first few cell divisions, although this is properly referred to as a morula.

In mammalian reproduction, after fertilization has taken place the zygote travels down the fallopian tube, while dividing to form more cells[2] without the zygote actually increasing in size. This cell division is mitotic, and is known as cleavage.[3] All mammals go through the zygote stage of life. Zygotes eventually develop into an embryo, and then a fetus. A human zygote exists for about four days, and becomes a blastocyst on the fifth day.[4]

Twins

Twins and multiple births can be monozygotic (identical) or dizygotic (fraternal). Dizygotic twins arise from one or several — strictly, two — fertilization events. Polyspermic zygotes in mice have been manipulated so as to remove one of the two male pronuclei and made to survive birth.[5]

Conjoined twins, sometimes called "Siamese twins", occur once in every two hundred identical twin pregnancies and are always identical. Actual numbers for conjoined births vary from 1 in 20,000 to 1 in 100,000 pregnancies; 40–60% are stillborn, with many others dying within the first few days after birth. About 70% of conjoined twins are female, the reason for which is unknown.

The first successful separation of conjoined twins was performed in Basle, Switzerland in 1689 on twin girls born joined by a ligament at the sternum (xiphopagus). The first to be successfully separated in modern times are generally believed to be Catherine and Caroline Mouton of Louisiana, born joined at the lower back (pygopagus) and separated in 1953 at eight days of age. Both survived the operation. Separation has been attempted on almost all conjoined twins born since the 1950s, with varying results.

In other species

A biparental zygote is a Chlamydomonas (a kind of algae) zygote that contains chloroplast DNA (cpDNA) from both parents.


See also

References

  1. ↑ English etymology of zygote. myetymology.com.
  2. ↑ O’Reilly, Deirdre. “Fetal development,” MedlinePlus Medical Encyclopedia (2007-10-19). Retrieved 2009-02-15.
  3. ↑ Klossner, N. Jayne and Hatfield, Nancy. Introductory Maternity & Pediatric Nursing, p. 107 (Lippincott Williams & Wilkins, 2006).
  4. ↑ Blackburn, Susan. Maternal, Fetal, & Neonatal Physiology, p. 80 (Elsevier Health Sciences 2007).
  5. ↑ Birth of normal mice after removal of the supernumerary male pronucleus from polyspermic zygotes all zygotes are halpliods.. National Center for Biotechnology Information.
Preceded by:
Oocyte
Sperm 		Stages of human development
Zygote 		Succeeded by:
Embryo
Mammalian development of embryo and development and fetus (some dates are approximate - see Carnegie stages) - edit

Week 1: Zygote | Morula | Blastula/Blastomere/Blastosphere | Archenteron/Primitive streak | Blastopore | Allantois | Trophoblast (Cytotrophoblast | Syncytiotrophoblast | Gestational sac)

Week 2: Yolk sac | Vitelline duct | Bilaminar disc

Week 3: Hensen's node | Gastrula/Gastrulation | Trilaminar embryo Branchial arch (1st) | Branchial pouch | Meckel's cartilage | Somite/Somitomere | Germ layer (Ectoderm, Endoderm, Mesoderm, Chordamesoderm, Paraxial mesoderm, Intermediate mesoderm, Lateral plate mesoderm)

Histogenesis and Organogenesis

Circulatory system: Primitive atrium | Primitive ventricle | Bulbus cordis | Truncus arteriosus | Ostium primum | Foramen ovale | Ductus venosus | Ductus arteriosus | Aortic arches | Septum primum | Septum secundum | Cardinal veins

Nervous system: Neural development/Neurulation | Neurula | Neural folds | Neural groove | Neural tube | Neural crest | Neuromere (Rhombomere) | Notochord | Optic vesicles | Optic stalk | Optic cup

Digestive system: Foregut | Midgut | Hindgut | Proctodeum | Rathke's pouch | Septum transversum

Urinary/Reproductive system: Urogenital folds | Urethral groove | Urogenital sinus | Kidney development (Pronephros | Mesonephros | Ureteric bud | Metanephric blastema) | Fetal genital development (Wolffian duct | Müllerian duct | Gubernaculum | Labioscrotal folds)

Glands: Thyroglossal duct

Uterine support: Placenta | Umbilical cord (Umbilical artery, Umbilical vein, Wharton's jelly) | Amniotic sac (Amnion, Chorion)

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