ægcelle

An ægcelle, commonly translated as egg cell or oocyte, is the female gamete in sexually reproducing organisms. It is typically large and rich in cytoplasm, containing maternal RNA, proteins, and organelles that support early embryo development. The egg's genome is haploid, carrying one set of chromosomes after meiosis, and its cytoplasm provides factors essential for the zygote’s initial growth.

In animals, the egg is produced by oogenesis in the ovaries. In mammals, eggs are surrounded by protective layers such as the cumulus cells, the zona pellucida, and, after ovulation, the corona radiata. Mature eggs are released during ovulation and, upon fertilization, complete meiosis II to form a zygote and a second polar body. The egg contributes the majority of the cytoplasm and maternal determinants that direct early development until the embryo can transcribe its own genome.

In humans and many other species, egg development involves a prolonged arrest in prophase I during fetal life, with meiosis resumes at puberty to form a secondary oocyte that can be fertilized. Fertilization typically triggers the completion of meiosis II, producing a diploid zygote.

In plants, the term also applies to the female gamete within the embryo sac of flowering plants (angiosperms). The egg cell is located at the micropylar end and is part of the egg apparatus with two synergids. After fertilization by a sperm cell, the egg forms a zygote that develops into the embryo; a second sperm usually fertilizes the central cell to form endosperm.

Overall, the ægcelle is the female gamete that provides half the genetic material and the cytoplasmic resources necessary to initiate development after fertilization.