Spermatogenesis and oogenesis are the processes by which gametes (sperm and eggs) are produced in the male and female reproductive systems. Spermatogenesis occurs in the seminiferous tubules of the testes and involves the production of sperm through meiosis and differentiation. Oogenesis begins during embryonic development with the formation of oocytes, and involves meiosis, follicular growth, and ovulation of a secondary oocyte from the ovaries each menstrual cycle. Fertilization occurs when a sperm fuses with an egg in the fallopian tubes, forming a zygote.