Spermatogenesis is male gametogenesis, the process in males by which diploid cells are reduced to haploid gametes. In a male fetus, the primordial germ cells migrate to the developing testes. Here, they undergo 20-30 mitotic divisions to generate a population of spermatogonia in the seminiferous tubules. At puberty, some of the spermatogonia begin the final differentiation into male gametes or sperm. The first step in this sequence is development into a primary spermatocyte. These are diploid cells with the normal number of 46 chromosomes that replicate their total DNA and enter meiosis. After the first meiotic division, the reduction division, a group of secondary spermatocytes containing only half of the normal human chromosome complement, or 23 chromosomes, is produced. Each secondary spermatocyte then undergoes a second cell division, that of meiosis II, resulting in two haploid spermatids. In this way, a total of four haploid spermatids are generated from each...