Zygote: Difference between revisions
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==Twins== |
==Twins== |
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[[Twin]]s and [[multiple birth]]s can be monozygotic (identical) or dizygotic (fraternal), meaning they 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 |publisher=National Center for Biotechnology Information}}</ref> |
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==Siamese/Conjoined Twins== |
==Siamese/Conjoined Twins== |
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Revision as of 13:48, 29 April 2009
 | This article may require copy editing for grammar, style, cohesion, tone, or spelling. (March 2009) |
- For other meanings see Zygote (disambiguation).
A zygote (or zygocyte) (from Greek ζυγωτός zugōtos "joined" or "yoked", from ζυγοῦν zugoun "to join" or "to yoke")[1] is a term in Developmental biology used to describe the first stage of a new unique organism when it consists of just a single cell. The term 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 blastomere. A zygote is 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. Thus the zygote contains (DNA) originating from both mother and father and this provides all the genetic information necessary to form a new individual.
In mammal reproduction, after fertilization has taken place the zygote travels down the fallopian tube, while dividing to form more cells[2] without the zygote actually gaining in size. This cell division is mitotic, and is known as "cleavage". [3] All mammals go through the zygote stage of life. Zygotes will 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
Siamese/Conjoined Twins
Siamese or conjoined 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 8 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.
References
- ^ "English etymology of zygote". myetymology.com.
- ^ O’Reilly, Deirdre. “Fetal development,” MedlinePlus Medical Encyclopedia (2007-10-19). Retrieved 2009-02-15.
- ^ Klossner, N. Jayne and Hatfield, Nancy. Introductory Maternity & Pediatric Nursing, page 107 (Lippincott Williams & Wilkins, 2006).
- ^ Blackburn, Susan. Maternal, Fetal, & Neonatal Physiology, page 80 (Elsevier Health Sciences 2007).