oocyt

Oocyt is commonly a misspelling of oocyte. An oocyte is the female gamete, the cell involved in reproduction that combines with a male gamete during fertilization to form a zygote. In most animals, oocytes develop in the ovaries through a process called oogenesis.

In humans and other mammals, oogenesis starts before birth when germ cells called oogonia proliferate and enter meiosis to become primary oocytes. These primary oocytes begin meiosis I but halt in prophase I until puberty. With each reproductive cycle, several follicles begin to mature, and usually one reaches ovulation as a secondary oocyte. This oocyte is arrested at metaphase II and will complete meiosis II only if fertilization occurs. If fertilization takes place, meiosis II completes, yielding a mature ovum and a second polar body.

Structure and composition vary among species, but mammalian oocytes generally have a large cytoplasm rich in nutrients and maternal factors to sustain early development. They are surrounded by a protective extracellular matrix called the zona pellucida and by cumulus cells that provide support. The oocyte contains mitochondria, ribosomes, and maternal mRNAs and proteins that guide early embryonic growth before zygotic genome activation. In eggs with substantial yolk, oocytes can be large and nutrient-dense; in mammals, yolk is relatively modest but still essential for initial embryo provisioning.

Clinical relevance includes assisted reproductive technologies such as in vitro fertilization and oocyte cryopreservation, as well as research into aging and oocyte quality, which influence fertility outcomes.