Oogenesis in humans occurs in ovaries and starts when diploid germ cells called oogonia grow and mature into primary oocytes enclosed in small follicles.

The primary oocytes start meiosis I, but stop at prophase I.

Beginning at puberty, periodic hormone secretions induce a few primary oocytes to complete meiosis I, each producing a non-functional polar body and a haploid secondary oocyte where most of the cytoplasm from the primary oocyte is concentrated.