Oositleri

Oositleri, or oocytes in Turkish, are the female gametes involved in sexual reproduction. They develop in the ovaries through oogenesis and serve as the cell that, when fertilized, combines with a male gamete to form a zygote. In humans and many other mammals, oocytes arise during fetal development and are housed in ovarian follicles. At birth, females possess millions of primary oocytes, which decline to around a few hundred thousand by puberty and only a fraction reach ovulation during reproductive years.

During development, oocytes proceed through meiosis in distinct stages. Primary oocytes are formed and arrested in prophase I before birth. At puberty, cyclic hormonal signals recruit cohorts of oocytes to resume meiosis I, producing a secondary oocyte and a first polar body. The secondary oocyte is released during ovulation and is arrested at metaphase II, remaining there until fertilization. Fertilization triggers the completion of meiosis II, yielding a mature ovum and a second polar body. Across species, the timing and exact control of these steps vary, but the general pattern of meiotic arrest, release, and completion is common.

Structure and composition are specialized for supporting early development. An oocyte is a relatively large cell with a surrounding zona pellucida and, in mammals, associated cumulus cells that provide metabolic support. The cytoplasm contains abundant maternal mRNA and proteins, mitochondria, and other resources that guide early embryonic development before zygotic genome activation.

Clinical relevance includes maternal age-related declines in oocyte quality and increases in aneuploidy risk. Oocytes are central to assisted reproductive technologies, including in vitro maturation, egg retrieval for in vitro fertilization, and cryopreservation. Across species, oocytes show considerable variation in yolk content and maturation dynamics.