Zygote


 * For other meanings see Zygote (disambiguation).

A zygote (Greek: ζυγωτόν) is a cell that is the result of fertilization. That is, two haploid cells&mdash;usually an ovum from a female and a sperm cell from a male&mdash;merge into a single diploid cell called the zygote (or zygocyte).

Fusion of the sperm with the ovacyte occurs in the Fallopian tube and the resulting diploid zygote becomes embedded in the uterus wall.

Animal zygotes undergo mitotic cell divisions to become an embryo. Other organisms may undergo meiotic cell division at this time (for more information refer to biological life cycles).

Twins
Twins and multiple births can be monozygotic (identical) or dizygotic (fraternal), meaning they arise from one or several (strictly, two) fertilization events.

A polyspermic zygote is a zygote that has been fetilized by more than one sperm. Each year, world wide, tens of thousands of zygotes derived from the in-vitro insemination of human oocytes undergo polyspermic fertilization. These embryos must presently be discarded because it has never been demonstrated in any humans that polyspermic zygotes can develop normally to term after removal of the supernumerary male pronucleus. However, polyspermic zygotes in mice have been manipulated so as to remove one of the two male pronuclei and made to survive birth.

In other species
A biparental zygote is a Chlamydomonas zygote that contains chloroplast DNA (cpDNA) from both parents.