zygote

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Dictionary: zy·gote (zī'gōt') pronunciation

The cell formed by the union of two gametes, especially a fertilized ovum before cleavage.
The organism that develops from a zygote.

[From Greek zugōtos, yoked, from zugoun, to yoke.]

zygotic zy·got'ic (-gŏt'ĭk) adj.
zygotically zy·got'i·cal·ly adv.

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World of the Body: zygote

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Derived from the Greek meaning ‘yoked’, a zygote is the cell that results from fertilization. It is the union of a spermatozoon and an ovum — the mature germ cells, known also as the male and female gametes (from the Greek for husband and wife). Each of the two gametes is haploid, meaning that the nucleus has half the number of chromosomes of normal body cells. Their union results in the diploid zygote, with a full set of chromosomes, carrying the combination of genes that will determine all the bodily characteristics of the new individual. When, as a result of this union, matched genes (alleles) at particular sites on the newly paired chromosomes are different from each other, the zygote, and hence the resulting individual, is heterozygous with respect to those genes. It is homozygous if the pairs are identical. Since one of a dissimilar pair of genes can dominate the other, whereas identical pairs can act in unison, this is crucial to the suppression or emergence of the relevant inherited trait.

The zygote carries within its single cell continuing threads in the immemorial lifespan of the human race, as well as the mixed-and-matched microscopic material from which will stem the intricacies common to all human bodies, yet with the remarkable uniqueness of a particular person.

— Sheila Jennett, Colin Blakemore

Dental Dictionary: zygote

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The developing ovum from the time it is fertilized until, as a blastocyst, it is implanted in the uterus.

Philosophy Dictionary: zygote

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(Greek, zygotos, yoked together) A cell formed by the union of two reproductive cells, or more broadly the developing organism produced by such a cell. The zygote is mentioned in debates about abortion as the smallest single ‘thing’ to which the history of a living individual can be traced.

Health Dictionary: zygote

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(zeye-goht)

The single cell that results from fertilization of an ovum by a sperm. After dividing several times, it implants in the uterus. It continues to divide, producing more cells and passing through the stages of embryo and fetus.

Veterinary Dictionary: zygote

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The cell resulting from union of a male and female gamete; the fertilized ovum. More precisely, the cell after synapsis at the completion of fertilization until first cleavage.

Wikipedia: Zygote

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For other uses, see Zygote (disambiguation).

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]

1 Twins
2 In other species
3 References
4 See also

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.

References

^ "English etymology of zygote". myetymology.com. http://www.myetymology.com/english/zygote.html.
^ 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, p. 107 (Lippincott Williams & Wilkins, 2006).
^ Blackburn, Susan. Maternal, Fetal, & Neonatal Physiology, p. 80 (Elsevier Health Sciences 2007).
^ "Birth of normal mice after removal of the supernumerary male pronucleus from polyspermic zygotes all zygotes are halpliods.". National Center for Biotechnology Information. http://www.ncbi.nlm.nih.gov/pubmed/8671222.

Preceded by Oocyte Sperm	Stages of human development Zygote	Succeeded by Embryo

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		Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more
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	Is a zygote a haploid? Read answer...
	How do you kill zygote? Read answer...
	How does a zygote form? Read answer...

	What is a diploid zygote?
	What does the cytoplasm of a zygote do?
	How do you kill a zygote?

zygote

Contents

Twins

In other species

References

See also