: spermatozoa; from Ancient Greek σπέρμα (spérma) 'seed' and ζῷον (zôion) 'animal') is a motile sperm cell produced by male animals relying on internal fertilization.

Sperm cells contribute approximately half of the nuclear genetic information to the diploid offspring (excluding, in most cases, mitochondrial DNA).

Sperm cells normally come in two types, "female" and "male", named for the resulting sex of the fertilized zygote each produces after fusing with the ovum.

[3] Errors of meiosis may lead to the formation of sperm containing different arrangements of sex chromosomes, either altogether missing (monosomy, designated "0"), or in multiples (trisomy), such as "XX", "XY", etc… some of the conditions known as Disorders of Sex Development (DSD) are the result of fertilization by such defective sperm.

[5] Sperm have an olfactory guidance mechanism, and after reaching the fallopian tubes, must undergo a period of capacitation before penetration of the ovum.

It also has a ring centriole (annulus) that form a diffusion barrier between the midpiece and the principal piece and serve as a stabilizing structure for tail rigidity.

[17] In particular, risk of aneuploidy is increased by tobacco smoking,[18][19] and occupational exposure to benzene,[20] insecticides,[21][22] and perfluorinated compounds.

[26] Thus mature spermatozoa appear to have a limited capacity to mount a DNA repair response to oxidative stress.

[32] The postmeiotic phase of mouse spermatogenesis is very sensitive to environmental genotoxic agents, because as male germ cells form mature spermatozoa they progressively lose the ability to repair DNA damage.

[33] Irradiation of male mice during late spermatogenesis can induce damage that persists for at least 7 days in the fertilizing spermatozoa, and disruption of maternal DNA double-strand break repair pathways increases spermatozoa-derived chromosomal aberrations.

[34] 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.

Algae and lower plant sperm cells are often multi-flagellated (see image) and thus morphologically different from animal spermatozoa.

[citation needed] Spermatozoa are produced in the seminiferous tubules of the testicles in a process called spermatogenesis.

In assisted reproductive technology, normozoospermia is referred to a total amount of >39 mill ejaculated, >32% with progressive motility and >4% normal morphology.

These problems are related to several complications in spermatozoa production, for example: Approaching the egg cell is a rather complex, multistep process of chemotaxis guided by different chemical substances/stimuli on individual levels of phylogeny.

Sperm activation has been shown to be caused by calcium ionophores in vitro, progesterone released by nearby cumulus cells and binding to ZP3 of the zona pellucida.

The cumulus cells are embedded in a gel-like substance made primarily of hyaluronic acid, and developed in the ovary with the egg and support it as it grows.

The whip-like tail (flagellum) of the sperm is studded with ion channels formed by proteins called CatSper.

The sudden rise in calcium levels causes the flagellum to form deeper bends, propelling the sperm more forcefully through the viscous environment.

It undergoes its secondary meiotic division, and the two haploid nuclei (paternal and maternal) fuse to form a zygote.

Almost 30-40% of infertility is due to male factor, so several strategies have been created in order to recover the functional spermatozoa.

The MMP (Million Motile Progressive cells per milliliter) measure is synonymous with capacitation, and is very useful parameter to decide, along with a spermiogram, the kind of treatment needed.

For example, if more than 1.0×106 progressive motile sperm per milliliter are found, it will be recommended to have sexual intercourse, and if that fails, the next step will be intrauterine insemination and later conventional in vitro fertilization.