23
Spermatogenesis As just noted, spermatogenesis occurs in the seminiferous tubules that form the bulk of each testis see Figure 27.4 . The process begins at puberty, after which time sperm are produced constantly throughout a mans life. One production cycle, from spermatogonia through formed sperm, takes approximately 64 days. A new cycle starts approximately every 16 days, although this timing is not synchronous across the seminiferous tubules. Sperm countsthe total number of sperm a man producesslowly decline after age 35, and some studies suggest that smoking can lower sperm counts irrespective of age. The process of spermatogenesis begins with mitosis of the diploid spermatogonia Figure 27.5 . Because these cells are diploid 2n , they each have a complete copy of the fathers genetic material, or 46 chromosomes. However, mature gametes are haploid 1n , containing 23 chromosomesmeaning that daughter cells of spermatogonia must undergo a second cellular division through the process of meiosis.