The egg cell

What is an egg?

The ovum (Oocyte) is the female reproductive cell of sexually reproducing organisms. Equipped with a haploid set of chromosomes, the circular oocyte reaches a diameter of approx. 0.01 cm in the mature state. During fertilization egg and sperm cells (23 chromosomes each) then merge into the zygote.
Oocytes in the context of oogenesis already develop prenatal (prenatal) in the fetus. At the onset of puberty, one oocyte, estimated to be about 250,000 to 500,000 oocytes, matures in the ovaries on each cycle. However, the number drops sharply with age. Over 99.9% of the eggs do not even get into the maturation process.
If one assumed for a long time that egg cells can no longer be reproduced after birth, US scientists showed the opposite in 2012: they discovered stem cells in the ovaries, which produced new egg cells even in adulthood.
Oocytes are gigantic in size compared to sperm (length of 0.0005 cm). In the cytoplasm of the egg cell, mitochondria, ribosomes and nuclear bodies are present, which play a significant role in the cell division after fertilization, since sperm practically only contribute their haploid set of chromosomes.