spermatid

Definition: The spermatid is the haploid male gametid that results from division of secondary spermatocytes. As a result of meiosis, each spermatid contains only half of the genetic material present in the original primary spermatocyte.

Spermatids are connected together by cytoplasmic material and have superfluous cytoplasmic material around their nuclei.

When formed, early round spermatids must undergo further maturational events in order to develop into spermatozoa, a process termed spermiogenesis (also termed spermeteliosis).

The spermatids begin to grow a living thread, develop a thickened mid-piece where the mitochondria become localised, and form an acrosome.

Spermatid DNA also undergoes packaging, becoming highly condensed. The DNA is packaged firstly with specific nuclear basic proteins, which are subsequently replaced with protamines during spermatid elongation.

The resultant tightly packed chromatin is transcriptionally inactive.

Spermatidogenesis

Spermatidogenesis is the creation of spermatids from secondary spermatocytes. Secondary spermatocytes produced earlier rapidly enter meiosis II and divide to produce haploid spermatids. The brevity of this stage means that secondary spermatocytes are rarely seen in histological preparations.