Spermatogonia proliferate by mitosis at puberty. Some enter meiosis to develop into sperm. Primary spermatocytes are diploid. They undergo meiosis I with the homologous chromosomes being distributed to daughter cells. After meiosis I, the developing sperm are called secondary spermatocytes. These enter meiosis II, in which the sister chromatids split at their centromeres and distribute to daughter cells called spermatids.
Some 300-400 million sperm are produced each day. They live about 48 hrs in the female reproductive tract. Sperm develop from spermatids by shedding their cytoplasm, rearranging their cytoplasm into an acrosome, and developing a flagellum. A sperm has a head, midpiece, and tail. The acrosome is in the head of the sperm. It contains enzymes that help the sperm penetrate to and into the ovum in the female. The midpiece has abundant mitochondria to provide energy for motility. The tail is a flagellum.
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