As a result of meiosis, each spermatid contains only half of the genetic material present in the original primary spermatocyte.

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

The DNA is packaged firstly with specific nuclear basic proteins, which are subsequently replaced with protamines during spermatid elongation.

[2] The conventional non-homologous end joining pathway for repairing double-strand breaks is not available for elongated spermatids.

[4] As postmeiotic germ cells develop to mature sperm they progressively lose the ability to repair DNA damage that may then accumulate and be transmitted to the zygote and ultimately the embryo.