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A zygote (from ζυγωτός zygōtos "joined" or "yoked", from ζυγοῦν zygoun "to join" or "to yoke"), is the initial formed when two cells are joined by means of . In multicellular organisms, it is the earliest developmental stage of the . In single-celled organisms, the zygote divides to produce offspring, usually through , the process of cell division.

A zygote is always synthesized from the union of two gametes, and constitutes the first stage in a unique organism's . Zygotes are usually produced by a event between two cells—an ( gamete) and a cell ( gamete)—which combine to form the single cell. Such zygotes contain derived from both parents, and this provides all the genetic information necessary to form a new individual. In , the zygote is formed within a chamber called the . 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. With onset of the first cellular divisions, an animal zygote transforms into a , or a mass of cells.

In animal development, 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.Neas, John F. "Human Development". Embryology Atlas

In , after fertilization has taken place the zygote travels down the , while O’Reilly, Deirdre. " Fetal development". (2007-10-19). Retrieved 2009-02-15. without the zygote actually increasing in size. This cell division is , and is known as .Klossner, N. Jayne and Hatfield, Nancy. cleavage blastocyst&as_brr=3&ei=mJaYSbj2CZjEM-Hc9KQJ Introductory Maternity & Pediatric Nursing, p. 107 (, 2006). All mammals go through the zygote stage of life. Mammalian zygotes eventually develop into a , after which they are more generally termed an embryo, and then a .

A human zygote exists as a single cell before undergoing cleavage, forming , Blastomere Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica Inc., 2012. Web. 06 Feb. 2012. and becomes a on the fifth day.Blackburn, Susan. Maternal, Fetal, & Neonatal Physiology, p. 80 (Elsevier Health Sciences 2007).

In other species
A biparental zygote is a (a kind of ) zygote that contains DNA () from both parents.

See also

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