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Zygote

For other uses, see Zygote (disambiguation).
"Fertilized egg" redirects here. For the food product, see Balut (food).

A zygote (from Ancient Greek ζυγωτός (zygōtós) 'joined, yoked', from ζυγοῦν (zygoun) 'to join, to yoke') is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information necessary to form a new individual organism.

Zygote: egg cell after fertilization with a sperm. The male and female pronuclei are converging, but the genetic material is not yet united.

In multicellular organisms, the zygote is the earliest developmental stage. In humans and most other anisogamous organisms, a zygote is formed when an egg cell is fertilized by a sperm cell. In single-celled organisms, the zygote can divide asexually by mitosis to produce identical offspring.

German zoologists Oscar and Richard Hertwig made some of the first discoveries on animal zygote formation in the late 19th century.

Contents

In fungi, the sexual fusion of haploid cells is called karyogamy. The result of karyogamy is the formation of a diploid cell called the zygote or zygospore. This cell may then enter meiosis or mitosis depending on the life cycle of the species.

In plants, the zygote may be polyploid if fertilization occurs between meiotically unreduced gametes.

In 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.

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 2n 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 4n diploid. After approximately 30 hours from the time of fertilization, a fusion of the pronuclei and immediate mitotic division produce two 2n diploid daughter cells called blastomeres.

Between the stages of fertilization and implantation, the developing human is a preimplantation conceptus. There is some dispute about whether this conceptus should no longer be referred to as an embryo, but should now be referred to as a proembryo, which is the terminology that traditionally has been used to refer to plant life. Some ethicists and legal scholars make the argument that it is incorrect to call the conceptus an embryo because it will later differentiate into both intraembryonic and extraembryonic tissues, and can even split to produce multiple embryos (identical twins). Others have pointed out that so-called extraembryonic tissues are really part of the embryo's body that are no longer used after birth (much as milk teeth fall out after childhood). Further, as the embryo splits to form identical twins – leaving the original tissues intact – new embryos are generated, in a process similar to that of cloning an adult human. In the US the National Institutes of Health has determined that the traditional classification of pre-implantation embryo is still correct.

After fertilization, the conceptus travels down the oviduct towards the uterus while continuing to divide mitotically without actually increasing in size, in a process called cleavage. After four divisions, the conceptus consists of 16 blastomeres, and it is known as the morula. 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. When the blastocyst hatches from the zona pellucida, it can implant in the endometrial lining of the uterus and begin the embryonic stage of development.

The human zygote has been genetically edited in experiments designed to cure inherited diseases.

The formation of a totipotent zygote with the potential to produce a whole organism depends on epigenetic reprogramming. DNA demethylation of the paternal genome in the zygote appears to be an important part of epigenetic reprogramming. 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.

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.

In the amoeba, reproduction occurs by cell division of the parent cell: first the nucleus of the parent divides into two and then the cell membrane also cleaves, becoming two "daughter" Amoebae.

  1. "English etymology of zygote". etymonline.com. Archived from the original on 2017-03-30.
  2. Blastomere Encyclopædia Britannica Archived 2013-09-28 at the Wayback Machine. Encyclopædia Britannica Online. Encyclopædia Britannica Inc., 2012. Web. 06 Feb. 2012.
  3. Larsen's Human Embryology. 4th Ed. Page 4.
  4. Condic, Maureen L. (14 April 2014). "Totipotency: What It Is And What It Is Not". Stem Cells and Development. 23 (8): 796–812. doi:10.1089/scd.2013.0364. PMC3991987. PMID 24368070.
  5. "Report of the Human Embryo Research Panel"(PDF). Archived from the original(PDF) on 2009-01-30. Retrieved2009-02-17.
  6. O’Reilly, Deirdre. "Fetal development Archived 2011-10-27 at the Wayback Machine". MedlinePlus Medical Encyclopedia (2007-10-19). Retrieved 2009-02-15.
  7. Klossner, N. Jayne and Hatfield, Nancy. Introductory Maternity & Pediatric Nursing, p. 107 (Lippincott Williams & Wilkins, 2006).
  8. Neas, John F. "Human Development" Archived July 22, 2011, at the Wayback Machine. Embryology Atlas
  9. Blackburn, Susan. Maternal, Fetal, & Neonatal Physiology, p. 80 (Elsevier Health Sciences 2007).
  10. "Editing human germline cells sparks ethics debate". May 6, 2015. Archived from the original on May 18, 2015. RetrievedMay 17, 2020.
  11. Ladstätter S, Tachibana-Konwalski K (December 2016). "A Surveillance Mechanism Ensures Repair of DNA Lesions during Zygotic Reprogramming". Cell. 167 (7): 1774–1787.e13. doi:10.1016/j.cell.2016.11.009. PMC5161750. PMID 27916276.
Preceded by Stages of human development
Zygote
Succeeded by

Zygote
Zygote Article Talk Language Watch Edit For other uses see Zygote disambiguation Fertilized egg redirects here For the food product see Balut food A zygote from Ancient Greek zygwtos zygōtos joined yoked from zygoῦn zygoun to join to yoke 1 is a eukaryotic cell formed by a fertilization event between two gametes The zygote s genome is a combination of the DNA in each gamete and contains all of the genetic information necessary to form a new individual organism Zygote egg cell after fertilization with a sperm The male and female pronuclei are converging but the genetic material is not yet united Zygote cell DetailsDays0PrecursorGametesGives rise toBlastomeresIdentifiersMeSHD015053TEE2 0 1 2 0 0 9FMA72395Anatomical terminology edit on Wikidata In multicellular organisms the zygote is the earliest developmental stage In humans and most other anisogamous organisms a zygote is formed when an egg cell is fertilized by a sperm cell In single celled organisms the zygote can divide asexually by mitosis to produce identical offspring German zoologists Oscar and Richard Hertwig made some of the first discoveries on animal zygote formation in the late 19th century Contents 1 Fungi 2 Plants 3 Humans 4 Reprogramming to totipotency 5 In other species 6 In protozoa 7 See also 8 ReferencesFungi EditIn fungi the sexual fusion of haploid cells is called karyogamy The result of karyogamy is the formation of a diploid cell called the zygote or zygospore This cell may then enter meiosis or mitosis depending on the life cycle of the species Plants EditIn plants the zygote may be polyploid if fertilization occurs between meiotically unreduced gametes In 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 Humans EditMain articles Development of the human body and Human fertilization 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 2n 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 4n diploid After approximately 30 hours from the time of fertilization a fusion of the pronuclei and immediate mitotic division produce two 2n diploid daughter cells called blastomeres 2 Between the stages of fertilization and implantation the developing human is a preimplantation conceptus There is some dispute about whether this conceptus should no longer be referred to as an embryo but should now be referred to as a proembryo which is the terminology that traditionally has been used to refer to plant life Some ethicists and legal scholars make the argument that it is incorrect to call the conceptus an embryo because it will later differentiate into both intraembryonic and extraembryonic tissues 3 and can even split to produce multiple embryos identical twins Others have pointed out that so called extraembryonic tissues are really part of the embryo s body that are no longer used after birth much as milk teeth fall out after childhood Further as the embryo splits to form identical twins leaving the original tissues intact new embryos are generated in a process similar to that of cloning an adult human 4 In the US the National Institutes of Health has determined that the traditional classification of pre implantation embryo is still correct 5 After fertilization the conceptus travels down the oviduct towards the uterus while continuing to divide 6 mitotically without actually increasing in size in a process called cleavage 7 After four divisions the conceptus consists of 16 blastomeres and it is known as the morula 8 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 9 When the blastocyst hatches from the zona pellucida it can implant in the endometrial lining of the uterus and begin the embryonic stage of development The human zygote has been genetically edited in experiments designed to cure inherited diseases 10 Reprogramming to totipotency EditThe formation of a totipotent zygote with the potential to produce a whole organism depends on epigenetic reprogramming DNA demethylation of the paternal genome in the zygote appears to be an important part of epigenetic reprogramming 11 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 11 In other species EditA 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 In protozoa EditIn the amoeba reproduction occurs by cell division of the parent cell first the nucleus of the parent divides into two and then the cell membrane also cleaves becoming two daughter Amoebae See also EditBreastfeeding and fertility Fertilization ProembryoReferences Edit English etymology of zygote etymonline com Archived from the original on 2017 03 30 Blastomere Encyclopaedia Britannica Archived 2013 09 28 at the Wayback Machine Encyclopaedia Britannica Online Encyclopaedia Britannica Inc 2012 Web 06 Feb 2012 Larsen s Human Embryology 4th Ed Page 4 Condic Maureen L 14 April 2014 Totipotency What It Is And What It Is Not Stem Cells and Development 23 8 796 812 doi 10 1089 scd 2013 0364 PMC 3991987 PMID 24368070 Report of the Human Embryo Research Panel PDF Archived from the original PDF on 2009 01 30 Retrieved 2009 02 17 O Reilly Deirdre Fetal development Archived 2011 10 27 at the Wayback Machine MedlinePlus Medical Encyclopedia 2007 10 19 Retrieved 2009 02 15 Klossner N Jayne and Hatfield Nancy Introductory Maternity amp Pediatric Nursing p 107 Lippincott Williams amp Wilkins 2006 Neas John F Human Development Archived July 22 2011 at the Wayback Machine Embryology Atlas Blackburn Susan Maternal Fetal amp Neonatal Physiology p 80 Elsevier Health Sciences 2007 Editing human germline cells sparks ethics debate May 6 2015 Archived from the original on May 18 2015 Retrieved May 17 2020 a b Ladstatter S Tachibana Konwalski K December 2016 A Surveillance Mechanism Ensures Repair of DNA Lesions during Zygotic Reprogramming Cell 167 7 1774 1787 e13 doi 10 1016 j cell 2016 11 009 PMC 5161750 PMID 27916276 Preceded byOocyte Sperm Stages of human development Zygote Succeeded byEmbryo Retrieved from https en wikipedia org w index php title Zygote amp oldid 1050990168, wikipedia, wiki, book,

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