Oogenesis

Step 1 (Fetal Stage)

Oogonia (2N) develop into primary oocytes (2N). These primary oocytes begin meiosis I but get arrested at Prophase I before the child is born.

Step 2 (Childhood)

The primary oocytes (2N) remain completely inactive and frozen in prophase 1 for years until puberty starts

Step 3 (Follicle Maturation)

Once puberty hits, hormonal changes cause a primary oocyte (2N) to complete meiosis I. This creates a secondary oocyte (n) and a first polar body which dies

Step 4 (Ovulation)

The secondary oocyte immediately enters meiosis II but gets arrested at metaphase II. It is then ovulated out of the ovary and awaiting fertilization

Step 5 (Fertilization)

If a sperm penetrates the secondary oocyte, it finishes meiosis II. Then after meiosis II it forms a zygote (2N) and seocnd polar body which dies