Ovum

Definition

The female gamete (egg cell) in sexually reproducing organisms, typically larger and non-motile relative to the male gamete (sperm). In arthropods, the ovum develops within the ovary, is released through the oviduct, and—once fertilized—initiates embryogenesis. The term distinguishes the functional gamete from the broader egg structure (egg = ovum plus accessory coverings such as chorion, yolk, and shell).

Etymology

Latin ovum, 'egg'

Example

In Drosophila melanogaster, the ovum is arrested in metaphase I of meiosis until ovulation; fertilization triggers completion of meiosis and the beginning of syncytial embryonic development.

Synonyms

• egg cell
• female gamete

Related Terms

• oocyte
• Oogenesis
• Ootheca
• Chorion
• Vitellogenesis
• spermatozoon
• zygote
• oviposition

Usage Notes

In entomology, 'ovum' refers strictly to the female gamete, whereas 'egg' commonly denotes the entire structure laid by the female (gamete plus egg membranes and associated materials). The plural 'ova' is standard in technical writing; 'ovums' is nonstandard. Contrast with 'oosphere' (non-motile female gamete in certain algae and fungi) and 'ootid' (the haploid cell produced by meiosis II that becomes the ovum proper).