This video shows two secondary spermatocytes, the parent cells of sperm that have just been born as a result of the first meiotic division of a primary spermatocyte, undergo the second meiotic division to form four haploid (i.e. having only one copy of each chromosome) spermatids. Besides meiosis, another important function of this division cycle is for cell components that will be needed by the mature sperm (e.g. nucleus, mitochondria, major sperm protein, and membranous organelles) to be shuttled into the forming spermatids, and for spermatocyte components no longer needed by the spermatids (e.g. meiotic spindle, ribosomes, Golgi, endoplasmic reticulum, actin cytoskeleton)--to be discarded. To jettison all these components, a central membrane-bound "garbage bag", called a residual body, is formed. At the end of the video, you'll see the large residual body surrounded by four spermatids. The spermatids are in a tetrahedral arrangement around the residual body; the spermatid at lower right is slightly out of the focal plane. The time box shows elapsed time in minutes:seconds. The division occurred in about a half hour. You can also see a scanning electron micrograph of spermatids and a residual body.
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