Eggcellen

Eggcellen is a term used to denote the female gamete, commonly called the egg cell or oocyte, in animals and figuratively in other eukaryotes. It typically carries a haploid complement of chromosomes and the cytoplasmic machinery required to support early embryonic development after fertilization.

In animals, oocytes develop in the ovaries through oogenesis. Primary oocytes undergo meiosis I to form a secondary oocyte and a small polar body; the secondary oocyte is usually arrested at metaphase II and completes meiosis only upon fertilization. Egg cells are relatively large, often contain yolk or nutrient stores, and are surrounded by protective layers such as the zona pellucida and somatic support cells (e.g., the corona radiata). Upon sperm entry, cortical granules trigger biochemical changes that prevent polyspermy.

Egg cells vary widely across taxa. In mammals they are small and non-yolky, relying on maternal provisioning and placental transfer; in birds, reptiles, and many invertebrates they may be large with abundant yolk to nourish the embryo. In flowering plants, the egg cell resides in the embryo sac within an ovule and participates in double fertilization: one sperm fuses with the egg to form the zygote and another with the central cell to form endosperm.

Egg cells are central to reproductive biology, assisted reproductive technologies (e.g., in vitro fertilization, cryopreservation), and developmental research. Ethical, legal, and medical considerations surround their use in fertility treatments, research, and conservation.