ReCGiP: Database of Reproduction Candidate Genes in Pigs based on bibliomics

Oogenesis

Oogenesis begins in the female embryo with differentiation of primordial germ cells into oogonia, ovary-specific stem cells. An oogonium multiplies by mitosis and begins meiosis, but the process stops at prophase . The cells at this stage, called primary oocyts, remain quiescent within small follicles until puberty. Beginning at puberty, follicle-stimulating hormone (FSH) periodically stimulates a follicle to grow and induces its primary oocyte to complete meiosis and start meiosis . Meiosis then stops again. Arrested at metaphase , the secondary oocyte is released at ovulation, when its follicle breaks open. Usually only one oocyte matures and is released each month. Meiosis does not continue until a sperm penetrates the oocyte; only then is oogenesis actually completed, producing an ovum.