How a spermatid differs from a sperm cell

Genetically a spermatid is same as a spermatozoa, but the two cells are absolutely different in appearance under microscope. Moreover the spermatozoa is highly motile. Spermatids are formed at the end of meiosis in male gonad, called testes. Spermatids are normal looking animal cell, with haploid number of chromosomes. Most of the cytoplasm is discarded from spermatid, golgi bodies give rise to a special vesicle where accumulation of lysosomal enzymes takes place and it is now termed acrosome, mitochondrial cloud and a flagella appear so that the cell can become motile.

NCBI Bookshelf. Molecular Biology of the Cell. New York: Garland Science; In most species, there are just two types of gamete , and they are radically different. The egg is among the largest cells in an organism, while the sperm spermatozoon , plural spermatozoa is often the smallest. The egg and the sperm are optimized in opposite ways for the propagation of the genes they carry.

Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules. These cells are called spermatogonial stem cells. The mitotic division of these produces two types of cells.

Haploid round spermatids undergo a remarkable transformation during spermiogenesis. The nucleus polarizes to one side of the cell as the nucleus condenses and elongates, and the microtubule-based manchette sculpts the nucleus into its species-specific head shape. The assembly of the central component of the sperm flagellum, known as the axoneme, begins early in spermiogenesis, and is followed by the assembly of secondary structures needed for normal flagella. The final remodelling of the mature elongated spermatid occurs during spermiation, when the spermatids line up along the luminal edge, shed their residual cytoplasm and are ultimately released into the lumen. Defects in spermiogenesis and spermiation are manifested as low sperm number, abnormal sperm morphology and poor motility and are commonly observed during reproductive toxicant administration, as well as in genetically modified mouse models of male infertility.