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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) The spermatids then undergo spermiogenesis to produce spermatozoa. ==Additional images== File:Gray1150.png|Transverse section of a tubule of the testis of a rat. X 250. File:Spermatocytogenesis.png|Schematic diagram of Spermatocytogenesis 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Spermatogonium」の詳細全文を読む スポンサード リンク
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