During which biological process is primary oocyte formation initiated?

Primary oocyte formation is initiated during oogenesis, which is the process of female gamete development. Oogenesis begins in the fetal ovaries, where oogonia (the precursor cells) divide mitotically to produce primary oocytes. These primary oocytes then enter prophase I of meiosis and become arrested in this stage until the female reaches sexual maturity.

This process is distinct from spermatogenesis, which refers specifically to the development of male gametes (sperm) and occurs in the testes. Fertilization is the event where a sperm cell joins with an egg cell, leading to the formation of a zygote, but it does not initiate oocyte formation. Cell division is a general term that encompasses various types of cellular replication and division processes but does not specify the particular pathway involved in oocyte development. Therefore, oogenesis is the accurate choice as it specifically refers to the formation of primary oocytes.