Figure 2.

Schematic of spermatogenesis in rodents. “A-single” (As), “A-paired” (Apr), and “A-aligned” (Aal) represent undifferentiated spermatogonia in the 1-, 2-, and 4-cells, respectively. During spermatogenic development, As spermatogonium undergoes one or more mitotic divisions to give rise to larger clones (chains) of interconnected cell sizes through transit-amplifying mitotic divisions. The image features 3–4 transit-amplifying divisions in the pool of undifferentiated As, Apr, and Aal spermatogonia, followed by 6 amplifying divisions in the pool of differentiated spermatogonia (A1–A4, Intermediate, and B-type) that give rise to primary spermatocytes. Two additional meiotic divisions produce the round spermatids that undergo spermiogenesis to produce sperm. Int, Intermediate.