Egg cell
The egg cell or ovum (pl.: ova) is the female reproductive cell, or gamete,[1] in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete is not capable of movement (non-motile). If the male gamete (sperm) is capable of movement, the type of sexual reproduction is also classified as oogamous. A nonmotile female gamete formed in the oogonium of some algae, fungi, oomycetes, or bryophytes is an oosphere.[2] When fertilized, the oosphere becomes the oospore.
"Ova" redirects here. For other uses, see Ova (disambiguation).When egg and sperm fuse during fertilisation, a diploid cell (the zygote) is formed, which rapidly grows into a new organism.
History[edit]
While the non-mammalian animal egg was obvious, the doctrine ex ovo omne vivum ("every living [animal comes from] an egg"), associated with William Harvey (1578–1657), was a rejection of spontaneous generation and preformationism as well as a bold assumption that mammals also reproduced via eggs. Karl Ernst von Baer discovered the mammalian ovum in 1827.[3][4] The fusion of spermatozoa with ova (of a starfish) was observed by Oskar Hertwig in 1876.[5][6]
Other organisms[edit]
In algae, the egg cell is often called oosphere. Drosophila oocytes develop in individual egg chambers that are supported by nurse cells and surrounded by somatic follicle cells. The nurse cells are large polyploid cells that synthesize and transfer RNA, proteins, and organelles to the oocytes. This transfer is followed by the programmed cell death (apoptosis) of the nurse cells. During oogenesis, 15 nurse cells die for every oocyte that is produced.[16] In addition to this developmentally regulated cell death, egg cells may also undergo apoptosis in response to starvation and other insults.[16]