A spermatogonium (plural: spermatogonia) is an undifferentiated male germ cell, originating in a seminiferous tubule and dividing into two primary spermatocytes (a kind of germ cell) in the production of spermatozoa.
There are three subtypes:
Type A(d) cells, with dark nuclei. These cells replicate to ensure a constant supply of spermatogonia to fuel spermatogenesis.
Type A(p) cells, with pale nuclei. These cells divide by mitosis to produce Type B cells.
Type B cells, which divide to give rise to primary spermatocytes.
Each primary spermatocyte duplicates its DNA and subsequently undergoes meiosis I to produce two haploid secondary spermatocytes. Each of the two secondary spermatocytes further undergo meiosis II to produce two spermatids (haploid). (1 primary spermatocyte => 4 spermatids)