Sperm
[2] Sperm cells form during the process known as spermatogenesis, which in amniotes (reptiles and mammals) takes place in the seminiferous tubules of the testicles.
[3] This process involves the production of several successive sperm cell precursors, starting with spermatogonia, which differentiate into spermatocytes.
[clarification needed] The nuclear DNA in sperm cells is haploid, that is, they contribute only one copy of each paternal chromosome pair.
[6] The mammalian sperm cell can be divided in 2 parts connected by a neck: During fertilization, the sperm provides three essential parts to the oocyte: (1) a signalling or activating factor, which causes the metabolically dormant oocyte to activate; (2) the haploid paternal genome; (3) the centriole, which is responsible for forming the centrosome and microtubule system.
Human sperm cells can survive within the female reproductive tract for more than 5 days post coitus.
Human sperm cells are particularly vulnerable to free radical attack and the generation of oxidative DNA damage,[19] such as that from 8-Oxo-2'-deoxyguanosine.
The postmeiotic phase of mouse spermatogenesis is very sensitive to environmental genotoxic agents, because as male germ cells form mature sperm they progressively lose the ability to repair DNA damage.
[21] Treatment of male mice with melphalan, a bifunctional alkylating agent frequently employed in chemotherapy, induces DNA lesions during meiosis that may persist in an unrepaired state as germ cells progress through DNA repair-competent phases of spermatogenic development.
Longer sperm cells are better than their shorter counterparts at displacing competitors from the female's seminal receptacle.
The benefit to females is that only healthy males carry "good" genes that can produce long sperm in sufficient quantities to outcompete their competitors.
More than 50 countries worldwide are importers of Danish sperm, including Paraguay, Canada, Kenya, and Hong Kong.
He described them as being animalcules (little animals), probably due to his belief in preformationism, which thought that each sperm contained a fully formed but small human.
[citation needed] Ejaculated fluids are detected by ultraviolet light, irrespective of the structure or colour of the surface.
[31][32] Sperm cells in algal and many plant gametophytes are produced in male gametangia (antheridia) via mitotic division.
[33] Motile sperm cells typically move via flagella and require a water medium in order to swim toward the egg for fertilization.
In animals most of the energy for sperm motility is derived from the metabolism of fructose carried in the seminal fluid.
[citation needed] Motile sperm are also produced by many protists and the gametophytes of bryophytes, ferns and some gymnosperms such as cycads and ginkgo.
They are produced in flask-shaped structures containing nectar, which attract flies that transfer the spermatia to nearby hyphae for fertilization in a mechanism similar to insect pollination in flowering plants.
