At birth the primary oocytes are allready in the prophase of
meiosis The first meiotic division takes place after puberty.Only 40.000 from 2 million oocytes present at birth remain at the beginning of puberty. A few of them mature during the ovarian cycle.
Usually, only one matures fully. One of the daughtercells, the secondary oocyte, receives most of the cytoplasm, the other forms the first polar body.
During ovulation the second meiotic division starts. It is only completed at when the oocyte is fertilized.
Blue : Zona Pellucida Red : Corona Radiata Green : Ovum