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Sperm (: sperm or sperms) is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, which are known as spermatozoa, while some red algae and fungi produce non-motile sperm cells, known as spermatia. contain non-motile sperm inside pollen, while some more basal plants like ferns and some have motile sperm.
Sperm cells form during the process known as spermatogenesis, which in ( and ) takes place in the seminiferous tubules of the . This process involves the production of several successive sperm cell precursors, starting with spermatogonia, which differentiate into . The spermatocytes then undergo meiosis, reducing their Ploidy by half, which produces . The spermatids then mature and, in animals, construct a tail, or flagellum, which gives rise to the mature, motile sperm cell. This whole process occurs constantly and takes around 3 months from start to finish.
Sperm cells cannot divide and have a limited lifespan, but after fusion with during fertilization, a new organism begins developing, starting as a totipotent zygote. The human sperm cell is haploid, so that its 23 can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. In mammals, sperm is stored in the epididymis and released through the penis in semen during ejaculation.
The word sperm is derived from the Greek word , sperma, meaning "seed".
A widespread hypothesis states that sperm evolved rapidly, but there is no direct evidence that sperm evolved at a fast rate or before other male characteristics.
The nuclear DNA in sperm cells is Ploidy, that is, they contribute only one copy of each paternal chromosome pair. Mitochondrion in human sperm contain no or very little DNA because mtDNA is degraded while sperm cells are maturing, hence they typically do not contribute any genetic material to their offspring.
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. (2025). 9780781737692, Lippincott Williams & Wilkins. ISBN 9780781737692
In 2016, scientists at Nanjing Medical University claimed they had produced cells resembling mouse spermatids from mouse embryonic stem cells artificially. They injected these spermatids into mouse eggs and produced pups.
DNA damages present in sperm cells in the period after meiosis but before fertilization may be repaired in the fertilized egg, but if not repaired, can have serious deleterious effects on fertility and the developing embryo. Human sperm cells are particularly vulnerable to free radical attack and the generation of oxidative DNA damage, (2025). 9783319188805 ISBN 9783319188805 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. Irradiation of male mice during late spermatogenesis can induce damage that persists for at least 7 days in the fertilizing sperm cells, and disruption of maternal DNA double-strand break repair pathways increases sperm cell-derived chromosomal aberrations. 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. Such unrepaired DNA damages in sperm cells, after fertilization, can lead to offspring with various abnormalities.
In addition to ejaculation, it is possible to extract sperm through testicular sperm extraction.
On the global market, Denmark has a well-developed system of human sperm export. This success mainly comes from the reputation of Danish sperm donors for being of high quality and, in contrast with the law in the other Nordic countries, gives donors the choice of being either anonymous or non-anonymous to the receiving couple. Assisted Reproduction in the Nordic Countries ncbio.org Furthermore, Nordic sperm donors tend to be tall and highly educated FDA Rules Block Import of Prized Danish Sperm Posted Aug 13, 08 7:37 AM CDT in World, Science & Health and have altruistic motives for their donations, partly due to the relatively low monetary compensation in Nordic countries. More than 50 countries worldwide are importers of Danish sperm, including Paraguay, Canada, Kenya, and Hong Kong. However, the Food and Drug Administration (FDA) of the US has banned import of any sperm, motivated by a risk of transmission of Creutzfeldt–Jakob disease, although such a risk is insignificant, since artificial insemination is very different from the route of transmission of Creutzfeldt–Jakob disease. The prevalence of Creutzfeldt–Jakob disease for donors is at most one in a million, and if the donor was a carrier, the infectious proteins would still have to cross the blood-testis barrier to make transmission possible.
Motile sperm are also produced by many and the gametophytes of , and some such as and ginkgo. The sperm cells are the only flagellated cells in the life cycle of these plants. In many ferns and , cycads and ginkgo they are multi-flagellated (carrying more than one flagellum).
In , the sperm cells are amoeboid and crawl, rather than swim, towards the egg cell.
Because spermatia cannot swim, they depend on their environment to carry them to the egg cell. Some , such as Polysiphonia, produce non-motile spermatia that are spread by water currents after their release. The spermatia of rust fungi are covered with a sticky substance. They are produced in flask-shaped structures containing nectar, which attract Fly that transfer the spermatia to nearby hyphae for fertilization in a mechanism similar to insect pollination in .
Fungal spermatia (also called pycniospores, especially in the Uredinales) may be confused with conidia. Conidia are that germinate independently of fertilization, whereas spermatia are that are required for fertilization. In some fungi, such as Neurospora crassa, spermatia are identical to microconidia as they can perform both functions of fertilization as well as giving rise to new organisms without fertilization.
In some , fertilization also involves sperm nuclei, rather than cells, migrating toward the egg cell through a fertilization tube. form sperm nuclei in a syncytium antheridium surrounding the egg cells. The sperm nuclei reach the eggs through fertilization tubes, similar to the pollen tube mechanism in plants.
History
Sperm were first observed in 1677 by Antonie van Leeuwenhoek using a microscope. He described them as being (little animals), probably due to his belief in preformationism, which thought that each sperm contained a fully formed but small human.
Forensic analysis
Ejaculated fluids are detected by Uv light, irrespective of the structure or colour of the surface. Sperm heads, e.g. from vaginal swabs, are still detected by microscopy using the "Christmas Tree Stain" method, i.e., Kernechtrot-Picroindigocarmine (KPIC) staining.
Sperm in plants
Sperm cells in algal and many plant are produced in male gametangia (antheridia) via mitotic division. In , sperm nuclei are produced inside pollen.
Motile sperm cells
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. This takes place in the mitochondria located in the sperm's midpiece (at the base of the sperm head). These cells cannot swim backwards due to the nature of their propulsion. The uniflagellated sperm cells (with one flagellum) of are referred to as spermatozoa, and are known to vary in size.
Non-motile sperm cells
Non-motile sperm cells called spermatia lack flagella and therefore cannot swim. Spermatia are produced in a Gametangium.
Sperm nuclei
In almost all , including most gymnosperms and all , the male gametophytes (pollen grains) are the primary mode of dispersal, for example via wind or insect pollination, eliminating the need for water to bridge the gap between male and female. Each pollen grain contains a spermatogenous (generative) cell. Once the pollen lands on the stigma of a receptive flower, it germinates and starts growing a pollen tube through the carpel. Before the tube reaches the ovule, the nucleus of the generative cell in the pollen grain divides and gives rise to two sperm nuclei, which are then discharged through the tube into the ovule for fertilization.
Sperm centrioles
Most sperm cells have centrioles in the sperm neck. Sperm of many animals has two typical centrioles, known as the proximal centriole and distal centriole. Some animals (including humans and bovines) have a single typical centriole, the proximal centriole, as well as a second centriole with atypical structure. Mice and rats have no recognizable sperm centrioles. The fruit fly Drosophila melanogaster has a single centriole and an atypical centriole named the proximal centriole-like.
Sperm tail formation
The sperm tail is a specialized type of cilium (aka flagella). In many animals the sperm tail is formed through the unique process of cytosolic ciliogenesis, in which all or part of the sperm tail's axoneme is formed in the cytoplasm or gets exposed to the cytoplasm.
See also
Citations
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