<P> To preserve the number of chromosomes in the offspring--which differs between species--each gamete must have half the usual number of chromosomes present in other body cells . Otherwise, the offspring will have twice the normal number of chromosomes, and serious abnormalities may result . In humans, chromosomal abnormalities arising from incorrect spermatogenesis results in congenital defects and abnormal birth defects (Down Syndrome, Klinefelter's Syndrome) and in most cases, spontaneous abortion of the developing foetus . </P> <P> Spermatogenesis takes place within several structures of the male reproductive system . The initial stages occur within the testes and progress to the epididymis where the developing gametes mature and are stored until ejaculation . The seminiferous tubules of the testes are the starting point for the process, where spermatogonial stem cells adjacent to the inner tubule wall divide in a centripetal direction--beginning at the walls and proceeding into the innermost part, or lumen--to produce immature sperm . Maturation occurs in the epididymis . The location (Testes / Scrotum) is specifically important as the process of spermatogenesis requires a lower temperature to produce viable sperm, specifically 1 ° - 8 ° C lower than normal body temperature of 37 ° C (98.6 ° F). Clinically, small fluctuations in temperature such as from an athletic support strap, causes no impairment in sperm viability or count . </P> <P> For humans, the entire process of spermatogenesis is variously estimated as taking 74 days (according to tritium - labelled biopsies) and approximately 120 days (according to DNA clock measurements). Including the transport on ductal system, it takes 3 months . Testes produce 200 to 300 million spermatozoa daily . However, only about half or 100 million of these become viable sperm . </P> <P> The entire process of spermatogenesis can be broken up into several distinct stages, each corresponding to a particular type of cell in humans . In the following table, ploidy, copy number and chromosome / chromatid counts are for one cell, generally prior to DNA synthesis and division (in G1 if applicable). The primary spermatocyte is arrested after DNA synthesis and prior to division . </P>

How often does spermatogeneis—the production of sperm—occur