Spermatogenesis and oogenesis are both forms of gametogenesis, a biological process by which precursor cells undergo cell division and differentiation to form mature haploid gametes. In spermatogenesis, gamete production is continuous, beginning at puberty. In oogenesis, the number of gametes is dependent on the amount of oocytes generated before birth, and the supply is exhausted at menopause.
Spermatogenesis is the process in which sperm cells are produced from male primordial germ cells by way of mitosis and meiosis. Spermatogonium, an undifferentiated germ cell in the seminiferous tubule of the testes, leads to a primary spermatocyte via mitosis. The primary spermatocyte is then divided into two secondary spermatocytes via meiosis I. The two secondary spermatocytes further undergo meiosis II, with each dividing into two spermatids. The spermatids then undergo spermiogenesis, maturing into sperm cells. The meiotic output per spermatogonium is four motile sperm cells.
In contrast, the meiotic output for oogenesis is one large, immotile oocyte. Oogenesis is the creation of an ovum, or egg cell, from female oocytes. Oogenesis begins in the germinal epithelium of the ovaries, where development of ovarian follicles occurs. Each follicle contains an oocyte, or immature ovum. Once every menstrual cycle, an individual oocyte is initiated to grow and develop. According to Wikipedia, Oogenesis is divided into three sub-processes: oocytogenesis, ootidogenesis and oogenesis proper. Oocytogenesis occurs during fetal development, when primordial follicles transform into primary oocytes.
During ootidogenesis, primary oocytes develop into ootids via meiosis. This process begins prior to birth but eventually halts at prophase I. The number of primary oocytes is set at a finite total around the time of birth. These primary oocytes remain at a state of prophase I until the first menstrual cycle. Afterwards, a few of these cells continue to develop every menstrual cycle. For those primary oocytes continuing meiosis I within a menstrual cycle, the cell divides into a secondary oocyte and the first polar body. Meiosis II begins immediately after, but the process is halted at the metaphase II stage until fertilization. If fertilization occurs, the secondary oocyte finishes meiosis II, creating an ootid and another polar body. The ootid matures into an ovum, and the polar bodies disintegrate.