title: Leech

text: The majority of leeches live in freshwater habitats, while some species can be found in terrestrial or marine environments. The best-known species, such as the medicinal leech, "Hirudo medicinalis", are hematophagous, attaching themselves to a host with a sucker and feeding on blood, having first secreted the peptide hirudin to prevent the blood from clotting. The jaws used to pierce the skin are replaced in other species by a proboscis which is pushed into the skin. A minority of leech species are predatory, mostly preying on small invertebrates.


title: Leech

text: The eggs are enclosed in a cocoon, which in aquatic species is usually attached to an underwater surface; members of one family, Glossiphoniidae, exhibit parental care, the eggs being brooded by the parent. In terrestrial species, the cocoon is often concealed under a log, in a crevice or buried in damp soil. Almost seven hundred species of leech are currently recognised, of which some hundred are marine, ninety terrestrial and the remainder freshwater.


title: Leech

text: Leeches have been used in medicine from ancient times until the 19th century to draw blood from patients. In modern times, leeches find medical use in treatment of joint diseases such as epicondylitis and osteoarthritis, extremity vein diseases, and in microsurgery, while hirudin is used as an anticoagulant drug to treat blood-clotting disorders.


title: Leech

text: Some 680 species of leech have been described, of which around 100 are marine, 480 freshwater and the remainder terrestrial. Among Euhirudinea, the true leeches, the smallest is about long, and the largest is the giant Amazonian leech, "Haementeria ghilianii", which can reach . Except for Antarctica, leeches are found throughout the world but are at their most abundant in temperate lakes and ponds in the northern hemisphere. The majority of freshwater leeches are found in the shallow, vegetated areas on the edges of ponds, lakes and slow-moving streams; very few species tolerate fast-flowing water. In their preferred habitats, they may occur in very high densities; in a favourable environment with water high in organic pollutants, over 10,000 individuals were recorded per square metre (over 930 per square foot) under rocks in Illinois. Some species aestivate during droughts, burying themselves in the sediment, and can lose up to 90% of their bodyweight and still survive. Among the freshwater leeches are the Glossiphoniidae, dorso-ventrally flattened animals mostly parasitic on vertebrates such as turtles, and unique among annelids in both brooding their eggs and carrying their young on the underside of their bodies.


title: Leech

text: The terrestrial Haemadipsidae are mostly native to the tropics and subtropics, while the aquatic Hirudinidae have a wider global range; both of these feed largely on mammals, including humans. A distinctive family is the Piscicolidae, marine or freshwater ectoparasites chiefly of fish, with cylindrical bodies and usually well-marked, bell-shaped, anterior suckers. Not all leeches feed on blood; the Erpobdelliformes, freshwater or amphibious, are carnivorous and equipped with a relatively large, toothless mouth to ingest insect larvae, molluscs, and other annelid worms, which are swallowed whole. In turn, leeches are prey to fish, birds, and invertebrates.


title: Leech

text: The name for the subclass, Hirudinea, comes from the Latin "hirudo" (genitive "hirudinis"), a leech; the element "-bdella" found in many leech group names is from the Greek βδέλλα "bdella", also meaning leech. The name "Les hirudinées" was given by Jean-Baptiste Lamarck in 1818. Leeches were traditionally divided into two infraclasses, the Acanthobdellidea (primitive leeches) and the Euhirudinea (true leeches). The Euhirudinea are divided into the proboscis-bearing Rhynchobdellida and the rest, including some jawed species, the "Arhynchobdellida", without a proboscis.


title: Leech

text: The phylogenetic tree of the leeches and their annelid relatives is based on molecular analysis (2019) of DNA sequences. Both the former classes "Polychaeta" (bristly marine worms) and "Oligochaeta" (including the earthworms) are paraphyletic: in each case the complete groups (clades) would include all the other groups shown below them in the tree. The Branchiobdellida are sister to the leech clade Hirudinida, which approximately corresponds to the traditional subclass Hirudinea. The main subdivision of leeches is into the Rhynchobdellida and the Arhynchobdellida, though the Acanthobdella are sister to the clade that contains these two groups.


title: Leech

text: The most ancient annelid group consists of the free-living polychaetes that evolved in the Cambrian period, being plentiful in the Burgess Shale about 500million years ago. Oligochaetes evolved from polychaetes and the leeches branched off from the oligochaetes. The oldest leech fossils are from the Jurassic period around 150million years ago, but a fossil with external ring markings found in Wisconsin in the 1980s, with what appears to be a large sucker, seems to extend the group's evolutionary history back to the Silurian, some 437million years ago.


title: Leech

text: Leeches show a remarkable similarity to each other in morphology, very different from typical annelids which are cylindrical with a fluid-filled space, the coelom (body cavity). In leeches, most of the coelom is filled with botryoidal tissue, a loose connective tissue composed of clusters of cells of mesodermal origin. The remaining body cavity has been reduced to four slender longitudinal channels. Typically, the body is dorso-ventrally flattened and tapers at both ends. Longitudinal and circular muscles in the body wall are supplemented by diagonal muscles, giving the leech the ability to adopt a large range of body shapes and show great flexibility. Most leeches have a sucker at both the anterior (front) and posterior (back) ends, but some primitive leeches have a single sucker at the back.


title: Leech

text: Like other annelids, the leech is a segmented animal, but unlike other annelids, the segmentation is masked by external ring markings (annulations). The number of annulations varies, both between different regions of the body and between species. In one species, the body surface is divided into 102 annuli, but the body consists of 33 segments, a number constant across all leech species. Of these segments, the first five are designated as the head and include the anterior brain, several ocelli (eyespots) dorsally and the sucker ventrally. The following 21 mid-body segments each contain a nerve ganglion, and between them contain two reproductive organs, a single female gonopore and nine pairs of testes. The last seven segments contain the posterior brain and are fused to form the animal's tail sucker. The septa that separates the body segments in the majority of annelids have been lost in leeches, except for the primitive genus Acanthobdella which still have some septa.


title: Leech

text: The body wall consists of a cuticle, an epidermis and a thick layer of fibrous connective tissue in which are embedded the circular muscles, the diagonal muscles and the powerful longitudinal muscles. There are also dorso-ventral muscles. In leeches the original blood vascular system has been lost and replaced by the modified coelom known as the haemocoelomic system, and the coelomic fluid, called the haemocoelomic fluid, has taken over the role as blood. The haemocoelomic channels run the full length of the body, the two main ones being on either side. Part of the lining epithelium consists of chloragogen cells which are used for the storage of nutrients and in excretion. There are 10 to 17 pairs of metanephridia (excretory organs) in the mid-region of the leech. From these, ducts typically lead to a urinary bladder, which empties to the outside at a nephridiopore.


title: Leech

text: Leeches are hermaphrodites, with the male reproductive organs, the testes, maturing first and the ovaries later. In hirudinids, a pair will line up with the clitellar regions in contact, with the anterior end of one leech pointing towards the posterior end of the other; this results in the male gonopore of one leech being in contact with the female gonopore of the other. The penis passes a spermatophore into the female gonopore and sperm is transferred to, and probably stored in, the vagina.


title: Leech

text: Some jawless leeches (Rhynchobdellida) and proboscisless leeches (Arhynchobdellida) lack a penis, and in these, sperm is passed from one individual to another by hypodermic injection. The leeches intertwine and grasp each other with their suckers. A spermatophore is pushed by one through the integument of the other, usually into the clitellar region. The sperm is liberated and passes to the ovisacs, either through the coelomic channels or interstitially through specialist "target tissue" pathways.


title: Leech

text: Some time after copulation, the small, relatively yolkless eggs are laid. In most species, an albumin-filled cocoon is secreted by the clitellum and receives one or more eggs as it passes over the female gonopore. In the case of the North American "Erpobdella punctata", the clutch size is about five eggs, and some ten cocoons are produced. Each cocoon is fixed to a submerged object, or in the case of terrestrial leeches, deposited under a stone or buried in damp soil. The cocoon of "Hemibdella soleae" is attached to a suitable fish host. The glossiphoniids brood their eggs, either by attaching the cocoon to the substrate and covering it with their ventral surface, or by securing the cocoon to their ventral surface, and even carrying the newly hatched young to their first meal.


title: Leech

text: When breeding, most marine leeches leave their hosts and become free-living in estuaries. Here they produce their cocoons, after which the adults of most species die. When the eggs hatch, the juveniles seek out potential hosts when these approach the shore. Leeches mostly have an annual or biannual life cycle.


title: Leech

text: About three quarters of leech species are parasites that feed on the blood of a host, while the remainder are predators. Leeches either have a pharynx that they can protrude, commonly called a proboscis, or a pharynx that they cannot protrude, which in some groups is armed with jaws.


title: Leech

text: In the proboscisless leeches, the jaws (if any) of Arhynchobdellids are at the front of the mouth, and have three blades set at an angle to each other. In feeding, these slice their way through the skin of the host, leaving a Y-shaped incision. Behind the blades is the mouth, located ventrally at the anterior end of the body. It leads successively into the pharynx, a short oesophagus, a crop (in some species), a stomach and a hindgut, which ends at an anus located just above the posterior sucker. The stomach may be a simple tube, but the crop, when present, is an enlarged part of the midgut with a number of pairs of ceca that store ingested blood. The leech secretes an anticoagulant, hirudin, in its saliva which prevents the blood from clotting before ingestion. A mature medicinal leech may feed only twice a year, taking months to digest a blood meal.


title: Leech

text: The bodies of predatory leeches are similar, though instead of a jaw many have a protrusible proboscis, which for most of the time they keep retracted into the mouth. Such leeches are often ambush predators that lie in wait until they can strike prey with the proboscises in a spear-like fashion. Predatory leeches feed on small invertebrates such as snails, earthworms and insect larvae. The prey is usually sucked in and swallowed whole. Some Rhynchobdellida however suck the soft tissues from their prey, making them intermediate between predators and blood-suckers.


title: Leech

text: Blood-sucking leeches use their anterior suckers to connect to hosts for feeding. Once attached, they use a combination of mucus and suction to stay in place while they inject hirudin into the hosts' blood. In general, blood-feeding leeches are non host-specific, and do little harm to their host, dropping off after consuming a blood meal. Some marine species however remain attached until it is time to reproduce. If present in great numbers on a host, these can be debilitating, and in extreme cases, cause death.


title: Leech

text: Leeches are unusual in that they do not produce certain digestive enzymes such as amylases, lipases or endopeptidases. A deficiency of these enzymes and of B complex vitamins is compensated for by enzymes and vitamins produced by endosymbiotic microflora. In "Hirudo medicinalis", these supplementary factors are produced by an obligatory mutualistic relationship with the bacterial species, "Aeromonas veronii". Non-bloodsucking leeches, such as "Erpobdella octoculata", are host to morew bacterial symbionts. In addition, leeches produce intestinal exopeptidases which remove amino acids from the long protein molecules one by one, possibly aided by proteases from endosymbiotic bacteria in the hindgut. This evolutionary choice of exopeptic digestion in Hirudinea distinguishes these carnivorous clitellates from oligochaetes, and may explain why digestion in leeches is so slow.


title: Leech

text: A leech's nervous system is formed of a few large nerve cells; their large size makes leeches convenient as model organisms for the study of invertebrate nervous systems. The main nerve centre consists of the cerebral ganglion above the gut and another ganglion beneath it, with connecting nerves forming a ring around the pharynx a little way behind the mouth. A nerve cord runs backwards from this in the ventral coelomic channel, with 21 pairs of ganglia in segments six to 26. In segments 27 to 33, other paired ganglia fuse to form the caudal ganglion. Several sensory nerves connect directly to the cerebral ganglion; there are sensory and motor nerve cells connected to the ventral nerve cord ganglia in each segment.


title: Leech

text: Leeches have between two and ten pigment spot ocelli, arranged in pairs towards the front of the body. There are also sensory papillae arranged in a lateral row in one annulation of each segment. Each papilla contains many sensory cells. Some rhynchobdellids have the ability to change colour dramatically by moving pigment in chromatophore cells; this process is under the control of the nervous system but its function is unclear as the change in hue seems unrelated to the colour of the surroundings.


title: Leech

text: Leeches can detect touch, vibration, movement of nearby objects, and chemicals secreted by their hosts; freshwater leeches crawl or swim towards a potential host standing in their pond within a few seconds. Species that feed on warm-blooded hosts move towards warmer objects. Many leeches avoid light, though some blood feeders move towards light when they are ready to feed, presumably increasing the chances of finding a host.


title: Leech

text: Leeches live in damp surroundings and in general respire through their body wall. The exception to this is in the Piscicolidae, where branching or leaf-like lateral outgrowths from the body wall form gills. Some rhynchobdellid leeches have an extracellular haemoglobin pigment, but this only provides for about half of the leech's oxygen transportation needs, the rest occurring by diffusion.


title: Leech

text: Leeches move using their longitudinal and circular muscles in a modification of the locomotion by peristalsis, self-propulsion by alternately contracting and lengthening parts of the body, seen in other annelids such as earthworms. They use their posterior and anterior suckers (one on each end of the body) to enable them to progress by looping or inching along, in the manner of geometer moth caterpillars. The posterior end is attached to the substrate, and the anterior end is projected forward peristaltically by the circular muscles until it touches down, as far as it can reach, and the anterior end is attached. Then the posterior end is released, pulled forward by the longitudinal muscles, and reattached; then the anterior end is released, and the cycle repeats. Leeches explore their environment with head movements and body waving. The Hirudinidae and Erpobdellidae can swim rapidly with up-and-down or sideways undulations of the body; the Glossiphoniidae in contrast are poor swimmers and curl up and fall to the sediment below when disturbed.


title: Leech

text: Leech bites are generally alarming rather than dangerous, though a small percentage of people have severe allergic or anaphylactic reactions and require urgent medical care. Symptoms of these reactions include red blotches or an itchy rash over the body, swelling around the lips or eyes, a feeling of faintness or dizziness, and difficulty in breathing. An externally attached leech will detach and fall off on its own accord when it is satiated on blood, which may take from twenty minutes to a few hours; bleeding from the wound may continue for some time. Internal attachments, such as inside the nose, are more likely to require medical intervention.


title: Leech

text: Bacteria, viruses, and protozoan parasites from previous blood sources can survive within a leech for months, so leeches could potentially act as vectors of pathogens. Nevertheless, only a few cases of leeches transmitting pathogens to humans have been reported.


title: Leech

text: Leech saliva is commonly believed to contain anaesthetic compounds to numb the bite area, but this has never been proven. Although morphine-like substances have been found in leeches, they have been found in the neural tissues, not the salivary tissues. They are used by the leeches in modulating their own immunocytes and not for anaesthetising bite areas on their hosts. Depending on the species and size, leech bites can be barely noticeable or they can be fairly painful.


title: Leech

text: The leech appears in Proverbs30:15 as an archetype of insatiable greed. More generally, a leech is a persistent social parasite or sycophant.


title: Leech

text: The medicinal leech "Hirudo medicinalis", and some other species, have been used for clinical bloodletting for at least 2,500 years: Ayurvedic texts describe their use for bloodletting in ancient India. In ancient Greece, bloodletting was practised according to the theory of humours found in the Hippocratic Corpus of the fifth centuryBC, which maintained that health depended on a balance of the four humours: blood, phlegm, black bile and yellow bile. Bloodletting using leeches enabled physicians to restore balance if they considered blood was present in excess.


title: Leech

text: Pliny the Elder reported in his "Natural History" that the horse leech could drive elephants mad by climbing up inside their trunks to drink blood. Pliny also noted the medicinal use of leeches in ancient Rome, stating that they were often used for gout, and that patients became addicted to the treatment. In Old English, "lǣce" was the name for a physician as well as for the animal, though the words had different origins, and "lǣcecraft", leechcraft, was the art of healing.


title: Leech

text: William Wordsworth's 1802 poem "Resolution and Independence" describes one of the last of the leech-gatherers, people who travelled Britain catching leeches from the wild, and causing a sharp decline in their abundance, though they remain numerous in Romney Marsh. By 1863, British hospitals had switched to imported leeches, some seven million being imported to hospitals in London that year.


title: Leech

text: In the nineteenth century, demand for leeches was sufficient for hirudiculture, the farming of leeches, to become commercially viable. Leech usage declined with the demise of humoral theory, but made a small-scale comeback in the 1980s after years of decline, with the advent of microsurgery, where venous congestion can arise due to inefficient venous drainage. Leeches can reduce swelling in the tissues and promote healing, helping in particular to restore circulation after microsurgery to reattach body parts. Other clinical applications include varicose veins, muscle cramps, thrombophlebitis, and joint diseases such as epicondylitis and osteoarthritis.


title: Leech

text: Leech secretions contain several bioactive substances with anti-inflammatory, anticoagulant and antimicrobial effects. One active component of leech saliva is a small protein, hirudin. It is widely used as an anticoagulant drug to treat blood-clotting disorders, and manufactured by recombinant DNA technology.


title: Leech

text: In 2012 and 2018, Ida Schnell and colleagues trialled the use of "Haemadipsa" leeches to gather data on the biodiversity of their mammalian hosts in the tropical rainforest of Vietnam, where it is hard to obtain reliable data on rare and cryptic mammals. They showed that mammal mitochondrial DNA, amplified by the polymerase chain reaction, can be identified from a leech's blood meal for at least four months after feeding. They detected Annamite striped rabbit, small-toothed ferret-badger, Truong Son muntjac, and serow in this way.


title: Leech

text: Exposure to synthetic estrogen as used in contraceptive medicines, which may enter freshwater ecosystems from municipal wastewater, can affect leeches' reproductive systems. Although not as sensitive to these compounds as fish, leeches showed physiological changes after exposure, including longer sperm sacs and vaginal bulbs, and decreased epididymis weight.


title: Meiosis

text: Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately result in four cells with only one copy of each chromosome (haploid). Additionally, prior to the division, genetic material from the paternal and maternal copies of each chromosome is crossed over, creating new combinations of code on each chromosome. Later on, during fertilisation, the haploid cells produced by meiosis from a male and female will fuse to create a cell with two copies of each chromosome again, the zygote.


title: Meiosis

text: Errors in meiosis resulting in aneuploidy (an abnormal number of chromosomes) are the leading known cause of miscarriage and the most frequent genetic cause of developmental disabilities.


title: Meiosis

text: In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells, each with half the number of chromosomes as the original parent cell. The two meiotic divisions are known as meiosis I and meiosis II. Before meiosis begins, during S phase of the cell cycle, the DNA of each chromosome is replicated so that it consists of two identical sister chromatids, which remain held together through sister chromatid cohesion. This S-phase can be referred to as "premeiotic S-phase" or "meiotic S-phase". Immediately following DNA replication, meiotic cells enter a prolonged G-like stage known as meiotic prophase. During this time, homologous chromosomes pair with each other and undergo genetic recombination, a programmed process in which DNA may be cut and then repaired, which allows them to exchange some of their genetic information. A subset of recombination events results in crossovers, which create physical links known as chiasmata (singular: chiasma, for the Greek letter Chi (Χ)) between the homologous chromosomes. In most organisms, these links can help direct each pair of homologous chromosomes to segregate away from each other during meiosis I, resulting in two haploid cells that have half the number of chromosomes as the parent cell.


title: Meiosis

text: During meiosis II, the cohesion between sister chromatids is released and they segregate from one another, as during mitosis. In some cases, all four of the meiotic products form gametes such as sperm, spores or pollen. In female animals, three of the four meiotic products are typically eliminated by extrusion into polar bodies, and only one cell develops to produce an ovum. Because the number of chromosomes is halved during meiosis, gametes can fuse (i.e. fertilization) to form a diploid zygote that contains two copies of each chromosome, one from each parent. Thus, alternating cycles of meiosis and fertilization enable sexual reproduction, with successive generations maintaining the same number of chromosomes. For example, diploid human


title: Meiosis

text: cells contain 23 pairs of chromosomes including 1 pair of sex chromosomes (46 total), half of maternal origin and half of paternal origin. Meiosis produces haploid gametes (ova or sperm) that contain one set of 23 chromosomes. When two gametes (an egg and a sperm) fuse, the resulting zygote is once again diploid, with the mother and father each contributing 23 chromosomes. This same pattern, but not the same number of chromosomes, occurs in all organisms that utilize meiosis.


title: Meiosis

text: Meiosis occurs in all sexually-reproducing single-celled and multicellular organisms (which are all eukaryotes), including animals, plants and fungi. It is an essential process for oogenesis and spermatogenesis.


title: Meiosis

text: Although the process of meiosis is related to the more general cell division process of mitosis, it differs in two important respects:


title: Meiosis

text: Meiosis begins with a diploid cell, which contains two copies of each chromosome, termed homologs. First, the cell undergoes DNA replication, so each homolog now consists of two identical sister chromatids. Then each set of homologs pair with each other and exchange genetic information by homologous recombination often leading to physical connections (crossovers) between the homologs. In the first meiotic division, the homologs are segregated to separate daughter cells by the spindle apparatus. The cells then proceed to a second division without an intervening round of DNA replication. The sister chromatids are segregated to separate daughter cells to produce a total of four haploid cells. Female animals employ a slight variation on this pattern and produce one large ovum and two small polar bodies. Because of recombination, an individual chromatid can consist of a new combination of maternal and paternal genetic information, resulting in offspring that are genetically distinct from either parent. Furthermore, an individual gamete can include an assortment of maternal, paternal, and recombinant chromatids. This genetic diversity resulting from sexual reproduction contributes to the variation in traits upon which natural selection can act.


title: Meiosis

text: Meiosis uses many of the same mechanisms as mitosis, the type of cell division used by eukaryotes to divide one cell into two identical daughter cells. In some plants, fungi, and protists meiosis results in the formation of spores: haploid cells that can divide vegetatively without undergoing fertilization. Some eukaryotes, like bdelloid rotifers, do not have the ability to carry out meiosis and have acquired the ability to reproduce by parthenogenesis.


title: Meiosis

text: Meiosis does not occur in archaea or bacteria, which generally reproduce asexually via binary fission. However, a "sexual" process known as horizontal gene transfer involves the transfer of DNA from one bacterium or archaeon to another and recombination of these DNA molecules of different parental origin.


title: Meiosis

text: Meiosis was discovered and described for the first time in sea urchin eggs in 1876 by the German biologist Oscar Hertwig. It was described again in 1883, at the level of chromosomes, by the Belgian zoologist Edouard Van Beneden, in "Ascaris" roundworm eggs. The significance of meiosis for reproduction and inheritance, however, was described only in 1890 by German biologist August Weismann, who noted that two cell divisions were necessary to transform one diploid cell into four haploid cells if the number of chromosomes had to be maintained. In 1911, the American geneticist Thomas Hunt Morgan detected crossovers in meiosis in the fruit fly "Drosophila melanogaster", which helped to establish that genetic traits are transmitted on chromosomes.


title: Meiosis

text: The term "meiosis" is derived from the Greek word , meaning 'lessening'. It was introduced to biology by J.B. Farmer and J.E.S. Moore in 1905, using the idiosyncratic rendering "maiosis":


title: Meiosis

text: "We propose to apply the terms Maiosis or Maiotic phase to cover the whole series of nuclear changes included in the two divisions that were designated as Heterotype and Homotype by Flemming".


title: Meiosis

text: The spelling was changed to "meiosis" by Koernicke (1905) and by Pantel and De Sinety (1906) to follow the usual conventions for transliterating Greek.


title: Meiosis

text: Meiosis is divided into meiosis I and meiosis II which are further divided into Karyokinesis I and Cytokinesis I and Karyokinesis II and Cytokinesis II respectively. The preparatory steps that lead up to meiosis are identical in pattern and name to interphase of the mitotic cell cycle. Interphase is divided into three phases:


title: Meiosis

text: Interphase is followed by meiosis I and then meiosis II. Meiosis I separates replicated homologous chromosomes, each still made up of two sister chromatids, into two daughter cells, thus reducing the chromosome number by half. During meiosis II, sister chromatids decouple and the resultant daughter chromosomes are segregated into four daughter cells. For diploid organisms, the daughter cells resulting from meiosis are haploid and contain only one copy of each chromosome. In some species, cells enter a resting phase known as interkinesis between meiosis I and meiosis II.


title: Meiosis

text: Meiosis I and II are each divided into prophase, metaphase, anaphase, and telophase stages, similar in purpose to their analogous subphases in the mitotic cell cycle. Therefore, meiosis includes the stages of meiosis I (prophase I, metaphase I, anaphase I, telophase I) and meiosis II (prophase II, metaphase II, anaphase II, telophase II).


title: Meiosis

text: During meiosis, specific genes are more highly transcribed. In addition to strong meiotic stage-specific expression of mRNA, there are also pervasive translational controls (e.g. selective usage of preformed mRNA), regulating the ultimate meiotic stage-specific protein expression of genes during meiosis. Thus, both transcriptional and translational controls determine the broad restructuring of meiotic cells needed to carry out meiosis.


title: Meiosis

text: Meiosis I segregates homologous chromosomes, which are joined as tetrads (2n, 4c), producing two haploid cells (n chromosomes, 23 in humans) which each contain chromatid pairs (1n, 2c). Because the ploidy is reduced from diploid to haploid, meiosis I is referred to as a "reductional division". Meiosis II is an "equational division" analogous to mitosis, in which the sister chromatids are segregated, creating four haploid daughter cells (1n, 1c).


title: Meiosis

text: Prophase I is by far the longest phase of meiosis (lasting 13 out of 14 days in mice). During prophase I, homologous maternal and paternal chromosomes pair, synapse, and exchange genetic information (by homologous recombination), forming at least one crossover per chromosome. These crossovers become visible as chiasmata (plural; singular chiasma). This process facilitates stable pairing between homologous chromosomes and hence enables accurate segregation of the chromosomes at the first meiotic division. The paired and replicated chromosomes are called bivalents (two chromosomes) or tetrads (four chromatids), with one chromosome coming from each parent. Prophase I is divided into a series of substages which are named according to the appearance of chromosomes.


title: Meiosis

text: The first stage of prophase I is the "leptotene" stage, also known as "leptonema", from Greek words meaning "thin threads". In this stage of prophase I, individual chromosomes—each consisting of two replicated sister chromatids—become "individualized" to form visible strands within the nucleus. The chromosomes each form a linear array of loops mediated by cohesin, and the lateral elements of the synaptonemal complex assemble forming an "axial element" from which the loops emanate. Recombination is initiated in this stage by the enzyme SPO11 which creates programmed double strand breaks (around 300 per meiosis in mice). This process generates single stranded DNA filaments coated by RAD51 and DMC1 which invade the homologous chromosomes, forming inter-axis bridges, and resulting in the pairing/co-alignment of homologues (to a distance of ~400 nm in mice).


title: Meiosis

text: Leptotene is followed by the "zygotene" stage, also known as "zygonema", from Greek words meaning "paired threads", which in some organisms is also called the bouquet stage because of the way the telomeres cluster at one end of the nucleus. In this stage the homologous chromosomes become much more closely (~100 nm) and stably paired (a process called synapsis) mediated by the installation of the transverse and central elements of the synaptonemal complex. Synapsis is thought to occur in a zipper-like fashion starting from a recombination nodule. The paired chromosomes are called bivalent or tetrad chromosomes.


title: Meiosis

text: The "pachytene" stage ( ), also known as "pachynema", from Greek words meaning "thick threads". is the stage at which all autosomal chromosomes have synapsed. In this stage homologous recombination, including chromosomal crossover (crossing over), is completed through the repair of the double strand breaks formed in leptotene. Most breaks are repaired without forming crossovers resulting in gene conversion. However, a subset of breaks (at least one per chromosome) form crossovers between non-sister (homologous) chromosomes resulting in the exchange of genetic information. Sex chromosomes, however, are not wholly identical, and only exchange information over a small region of homology called the pseudoautosomal region. The exchange of information between the homologous chromatids results in a recombination of information; each chromosome has the complete set of information it had before, and there are no gaps formed as a result of the process. Because the chromosomes cannot be distinguished in the synaptonemal complex, the actual act of crossing over is not perceivable through an ordinary light microscope, and chiasmata are not visible until the next stage.


title: Meiosis

text: During the "diplotene" stage, also known as "diplonema", from Greek words meaning "two threads", the synaptonemal complex disassembles and homologous chromosomes separate from one another a little. However, the homologous chromosomes of each bivalent remain tightly bound at chiasmata, the regions where crossing-over occurred. The chiasmata remain on the chromosomes until they are severed at the transition to anaphase I to allow homologous chromosomes to move to opposite poles of the cell.


title: Meiosis

text: In human fetal oogenesis, all developing oocytes develop to this stage and are arrested in prophase I before birth. This suspended state is referred to as the "dictyotene stage" or dictyate. It lasts until meiosis is resumed to prepare the oocyte for ovulation, which happens at puberty or even later.


title: Meiosis

text: Chromosomes condense further during the "diakinesis" stage, from Greek words meaning "moving through". This is the first point in meiosis where the four parts of the tetrads are actually visible. Sites of crossing over entangle together, effectively overlapping, making chiasmata clearly visible. Other than this observation, the rest of the stage closely resembles prometaphase of mitosis; the nucleoli disappear, the nuclear membrane disintegrates into vesicles, and the meiotic spindle begins to form.


title: Meiosis

text: Unlike mitotic cells, human and mouse oocytes do not have centrosomes to produce the meiotic spindle. In mice, approximately 80 MicroTubule Organizing Centers (MTOCs) form a sphere in the ooplasm and begin to nucleate microtubules that reach out towards chromosomes, attaching to the chromosomes at the kinetochore. Over time the MTOCs merge until two poles have formed, generating a barrel shaped spindle. In human oocytes spindle microtubule nucleation begins on the chromosomes, forming an aster that eventually expands to surround the chromosomes. Chromosomes then slide along the microtubules towards the equator of the spindle, at which point the chromosome kinetochores form end-on attachments to microtubules.


title: Meiosis

text: Homologous pairs move together along the metaphase plate: As "kinetochore microtubules" from both spindle poles attach to their respective kinetochores, the paired homologous chromosomes align along an equatorial plane that bisects the spindle, due to continuous counterbalancing forces exerted on the bivalents by the microtubules emanating from the two kinetochores of homologous chromosomes. This attachment is referred to as a bipolar attachment. The physical basis of the independent assortment of chromosomes is the random orientation of each bivalent along with the metaphase plate, with respect to the orientation of the other bivalents along the same equatorial line. The protein complex cohesin holds sister chromatids together from the time of their replication until anaphase. In mitosis, the force of kinetochore microtubules pulling in opposite directions creates tension. The cell senses this tension and does not progress with anaphase until all the chromosomes are properly bi-oriented. In meiosis, establishing tension ordinarily requires at least one crossover per chromosome pair in addition to cohesin between sister chromatids (see Chromosome segregation).


title: Meiosis

text: Kinetochore microtubules shorten, pulling homologous chromosomes (which each consist of a pair of sister chromatids) to opposite poles. Nonkinetochore microtubules lengthen, pushing the centrosomes farther apart. The cell elongates in preparation for division down the center. Unlike in mitosis, only the cohesin from the chromosome arms is degraded while the cohesin surrounding the centromere remains protected by a protein named Shugoshin (Japanese for "guardian spirit"), what prevents the sister chromatids from separating. This allows the sister chromatids to remain together while homologs are segregated.


title: Meiosis

text: The first meiotic division effectively ends when the chromosomes arrive at the poles. Each daughter cell now has half the number of chromosomes but each chromosome consists of a pair of chromatids. The microtubules that make up the spindle network disappear, and a new nuclear membrane surrounds each haploid set. The chromosomes uncoil back into chromatin. Cytokinesis, the pinching of the cell membrane in animal cells or the formation of the cell wall in plant cells, occurs, completing the creation of two daughter cells. However, cytokinesis does not fully complete resulting in "cytoplasmic bridges" which enable the cytoplasm to be shared between daughter cells until the end of meiosis II. Sister chromatids remain attached during telophase I.


title: Meiosis

text: Cells may enter a period of rest known as interkinesis or interphase II. No DNA replication occurs during this stage.


title: Meiosis

text: Meiosis II is the second meiotic division, and usually involves equational segregation, or separation of sister chromatids. Mechanically, the process is similar to mitosis, though its genetic results are fundamentally different. The end result is production of four haploid cells (n chromosomes, 23 in humans) from the two haploid cells (with n chromosomes, each consisting of two sister chromatids) produced in meiosis I. The four main steps of meiosis II are: prophase II, metaphase II, anaphase II, and telophase II.


title: Meiosis

text: In prophase II, we see the disappearance of the nucleoli and the nuclear envelope again as well as the shortening and thickening of the chromatids. Centrosomes move to the polar regions and arrange spindle fibers for the second meiotic division.


title: Meiosis

text: In metaphase II, the centromeres contain two kinetochores that attach to spindle fibers from the centrosomes at opposite poles. The new equatorial metaphase plate is rotated by 90 degrees when compared to meiosis I, perpendicular to the previous plate.


title: Meiosis

text: This is followed by anaphase II, in which the remaining centromeric cohesin, not protected by Shugoshin anymore, is cleaved, allowing the sister chromatids to segregate. The sister chromatids by convention are now called sister chromosomes as they move toward opposing poles.


title: Meiosis

text: The process ends with telophase II, which is similar to telophase I, and is marked by decondensation and lengthening of the chromosomes and the disassembly of the spindle. Nuclear envelopes re-form and cleavage or cell plate formation eventually produces a total of four daughter cells, each with a haploid set of chromosomes.


title: Meiosis

text: The new combinations of DNA created during meiosis are a significant source of genetic variation alongside mutation, resulting in new combinations of alleles, which may be beneficial. Meiosis generates gamete genetic diversity in two ways: (1) Law of Independent Assortment. The independent orientation of homologous chromosome pairs along the metaphase plate during metaphase I and orientation of sister chromatids in metaphase II, this is the subsequent separation of homologs and sister chromatids during anaphase I and II, it allows a random and independent distribution of chromosomes to each daughter cell (and ultimately to gametes); and (2) Crossing Over. The physical exchange of homologous chromosomal regions by homologous recombination during prophase I results in new combinations of genetic information within chromosomes.


title: Meiosis

text: Female mammals and birds are born possessing all the oocytes needed for future ovulations, and these oocytes are arrested at the prophase I stage of meiosis. In humans, as an example, oocytes are formed between three and four months of gestation within the fetus and are therefore present at birth. During this prophase I arrested stage (dictyate), which may last for decades, four copies of the genome are present in the oocytes. The arrest of ooctyes at the four genome copy stage was proposed to provide the informational redundancy needed to repair damage in the DNA of the germline. The repair process used appears to involve homologous recombinational repair Prophase I arrested oocytes have a high capability for efficient repair of DNA damages, particularly exogenously induced double-strand breaks. DNA repair capability appears to be a key quality control mechanism in the female germ line and a critical determinant of fertility.


title: Meiosis

text: Meiosis occurs in eukaryotic life cycles involving sexual reproduction, consisting of the constant cyclical process of meiosis and fertilization. This takes place alongside normal mitotic cell division. In multicellular organisms, there is an intermediary step between the diploid and haploid transition where the organism grows. At certain stages of the life cycle, germ cells produce gametes. Somatic cells make up the body of the organism and are not involved in gamete production.


title: Meiosis

text: Cycling meiosis and fertilization events produces a series of transitions back and forth between alternating haploid and diploid states. The organism phase of the life cycle can occur either during the diploid state ("diplontic" life cycle), during the haploid state ("haplontic" life cycle), or both ("haplodiplontic" life cycle, in which there are two distinct organism phases, one during the haploid state and the other during the diploid state). In this sense there are three types of life cycles that utilize sexual reproduction, differentiated by the location of the organism phase(s).


title: Meiosis

text: In the "diplontic life cycle" (with pre-gametic meiosis), of which humans are a part, the organism is diploid, grown from a diploid cell called the zygote. The organism's diploid germ-line stem cells undergo meiosis to create haploid gametes (the spermatozoa for males and ova for females), which fertilize to form the zygote. The diploid zygote undergoes repeated cellular division by mitosis to grow into the organism.


title: Meiosis

text: In the "haplontic life cycle" (with post-zygotic meiosis), the organism is haploid instead, spawned by the proliferation and differentiation of a single haploid cell called the gamete. Two organisms of opposing sex contribute their haploid gametes to form a diploid zygote. The zygote undergoes meiosis immediately, creating four haploid cells. These cells undergo mitosis to create the organism. Many fungi and many protozoa utilize the haplontic life cycle.


title: Meiosis

text: Finally, in the "haplodiplontic life cycle" (with sporic or intermediate meiosis), the living organism alternates between haploid and diploid states. Consequently, this cycle is also known as the alternation of generations. The diploid organism's germ-line cells undergo meiosis to produce spores. The spores proliferate by mitosis, growing into a haploid organism. The haploid organism's gamete then combines with another haploid organism's gamete, creating the zygote. The zygote undergoes repeated mitosis and differentiation to become a diploid organism again. The haplodiplontic life cycle can be considered a fusion of the diplontic and haplontic life cycles.


title: Meiosis

text: Meiosis occurs in all animals and plants. The end result, the production of gametes with half the number of chromosomes as the parent cell, is the same, but the detailed process is different. In animals, meiosis produces gametes directly. In land plants and some algae, there is an alternation of generations such that meiosis in the diploid sporophyte generation produces haploid spores. These spores multiply by mitosis, developing into the haploid gametophyte generation, which then gives rise to gametes directly (i.e. without further meiosis). In both animals and plants, the final stage is for the gametes to fuse, restoring the original number of chromosomes.


title: Meiosis

text: In females, meiosis occurs in cells known as oocytes (singular: oocyte). Each primary oocyte divides twice in meiosis, unequally in each case. The first division produces a daughter cell, and a much smaller polar body which may or may not undergo a second division. In meiosis II, division of the daughter cell produces a second polar body, and a single haploid cell, which enlarges to become an ovum. Therefore, in females each primary oocyte that undergoes meiosis results in one mature ovum and one or two polar bodies.


title: Meiosis

text: Note that there are pauses during meiosis in females. Maturing oocytes are arrested in prophase I of meiosis I and lie dormant within a protective shell of somatic cells called the follicle. At the beginning of each menstrual cycle, FSH secretion from the anterior pituitary stimulates a few follicles to mature in a process known as folliculogenesis. During this process, the maturing oocytes resume meiosis and continue until metaphase II of meiosis II, where they are again arrested just before ovulation. If these oocytes are fertilized by sperm, they will resume and complete meiosis. During folliculogenesis in humans, usually one follicle becomes dominant while the others undergo atresia. The process of meiosis in females occurs during oogenesis, and differs from the typical meiosis in that it features a long period of meiotic arrest known as the dictyate stage and lacks the assistance of centrosomes.


title: Meiosis

text: In males, meiosis occurs during spermatogenesis in the seminiferous tubules of the testicles. Meiosis during spermatogenesis is specific to a type of cell called spermatocytes, which will later mature to become spermatozoa. Meiosis of primordial germ cells happens at the time of puberty, much later than in females. Tissues of the male testis suppress meiosis by degrading retinoic acid, proposed to be a stimulator of meiosis. This is overcome at puberty when cells within seminiferous tubules called Sertoli cells start making their own retinoic acid. Sensitivity to retinoic acid is also adjusted by proteins called nanos and DAZL. Genetic loss-of-function studies on retinoic acid-generating enzymes have shown that retinoic acid is required postnatally to stimulate spermatogonia differentiation which results several days later in spermatocytes undergoing meiosis, however retinoic acid is not required during the time when meiosis initiates.


title: Meiosis

text: In female mammals, meiosis begins immediately after primordial germ cells migrate to the ovary in the embryo. Some studies suggest that retinoic acid derived from the primitive kidney (mesonephros) stimulates meiosis in embryonic ovarian oogonia and that tissues of the embryonic male testis suppress meiosis by degrading retinoic acid. However, genetic loss-of-function studies on retinoic acid-generating enzymes have shown that retinoic acid is not required for initiation of either female meiosis which occurs during embryogenesis or male meiosis which initiates postnatally.


title: Meiosis

text: While the majority of eukaryotes have a two-divisional meiosis (though sometimes achiasmatic), a very rare form, one-divisional meiosis, occurs in some flagellates (parabasalids and oxymonads) from the gut of the wood-feeding cockroach "Cryptocercus".


title: Meiosis

text: Recombination among the 23 pairs of human chromosomes is responsible for redistributing not just the actual chromosomes, but also pieces of each of them. There is also an estimated 1.6-fold more recombination in females relative to males. In addition, average, female recombination is higher at the centromeres and male recombination is higher at the telomeres. On average, 1 million bp (1 Mb) correspond to 1 cMorgan (cm = 1% recombination frequency). The frequency of cross-overs remain uncertain. In yeast, mouse and human, it has been estimated that ≥200 double-strand breaks (DSBs) are formed per meiotic cell. However, only a subset of DSBs (~5–30% depending on the organism), go on to produce crossovers, which would result in only 1-2 cross-overs per human chromosome.


title: Meiosis

text: The normal separation of chromosomes in meiosis I or sister chromatids in meiosis II is termed "disjunction". When the segregation is not normal, it is called "nondisjunction". This results in the production of gametes which have either too many or too few of a particular chromosome, and is a common mechanism for trisomy or monosomy. Nondisjunction can occur in the meiosis I or meiosis II, phases of cellular reproduction, or during mitosis.


title: Meiosis

text: Most monosomic and trisomic human embryos are not viable, but some aneuploidies can be tolerated, such as trisomy for the smallest chromosome, chromosome 21. Phenotypes of these aneuploidies range from severe developmental disorders to asymptomatic. Medical conditions include but are not limited to:


title: Meiosis

text: The probability of nondisjunction in human oocytes increases with increasing maternal age, presumably due to loss of cohesin over time.


title: Meiosis

text: In order to understand meiosis, a comparison to mitosis is helpful. The table below shows the differences between meiosis and mitosis.


title: Meiosis

text: How a cell proceeds to meiotic division in meiotic cell division is not well known. Maturation promoting factor (MPF) seemingly have role in frog Oocyte meiosis. In the fungus "S. pombe". there is a role of MeiRNA binding protein for entry to meiotic cell division.


title: Meiosis

text: It has been suggested that Yeast CEP1 gene product, that binds centromeric region CDE1, may play a role in chromosome pairing during meiosis-I.


title: Meiosis

text: Meiotic recombination is mediated through double stranded break, which is catalyzed by Spo11 protein. Also Mre11, Sae2 and Exo1 play role in breakage and recombination. After the breakage happen, recombination take place which is typically homologous. The recombination may go through either a double Holliday junction (dHJ) pathway or synthesis-dependent strand annealing (SDSA). (The second one gives to noncrossover product).


title: Meiosis

text: Seemingly there are checkpoints for meiotic cell division too. In S. pombe, Rad proteins, S. pombe Mek1 (with FHA kinase domain), Cdc25, Cdc2 and unknown factor is thought to form a checkpoint.


title: Meiosis

text: In vertebrate oogenesis, maintained by cytostatic factor (CSF) has role in switching into meiosis-II.


title: Ayesha Curry

text: Ayesha Disa Curry (née Alexander; born March 23, 1989) is a Canadian-American actress, cookbook author, and cooking television personality and the wife of basketball player Stephen Curry. After guest roles in several television shows and movies, she began hosting her own show, "Ayesha's Homemade" ( "Ayesha's Home Kitchen"), on Food Network. Despite not having any professional chef training, her culinary career started in 2014, when she prepared her first meal as a YouTube demonstration on her channel "Little Lights of Mine". Curry is the author of several videos on her channel Little Lights of Mine and has written two cookbooks, "The Seasoned Life", published in 2016, and "The Full Plate", published in 2020.


title: Ayesha Curry

text: At age 12, Curry acted as the love interest in the music video for "Too Young for Love" by Suga Prince (now known as Sevn Thomas).


title: Ayesha Curry

text: After graduating from Weddington High School, Curry moved to Los Angeles to become an actress, appearing, mostly, in bit parts. She was in a film short "Underground Street Flippers" (2009), The TV movie "Dan's Detour of Life" (2008), was Girl #1 in the direct to DVD movie "Love for Sale" (2008).


title: Ayesha Curry

text: After her marriage she started a food blog, and then a YouTube channel. This led to a short lived Food Network show "Ayesha's Homemade" that was canceled after 13 episodes. In addition to her written recipes, Curry often posts instructional cooking videos on her YouTube channel.


title: Ayesha Curry

text: In 2016, she released her cookbook "The Seasoned Life." She also began starring in "Ayesha's Homemade", which follows her professional and personal life with cameos from her husband and two daughters. The first season ran for six episodes. A second season of six episodes, named "Ayesha's Home Kitchen" premiered on Food Network on April 30, 2017.


title: Ayesha Curry

text: On September 20, 2017, Curry was named as a spokesperson for CoverGirl, becoming the first spokesperson for the brand who is not an actress or singer. She was announced on September 21, 2017, as one of the new hosts of "The Great American Baking Show", an American adaptation of "The Great British Bake Off", on ABC. She also revealed to Deidre Behar, from Entertainment Tonight, that she was approached to join the next season of "Dancing With The Stars." Only two episodes of the third season of "Baking Show", however, aired on television due to sexual harassment allegations against one of the show's judges outside the series. While the show was renewed for a fourth season, Curry did not return as a host and was succeeded by former Spice Girls member Emma Bunton.


title: Ayesha Curry

text: In July 2019, Curry and her husband launched the "Eat. Learn. Play. Foundation" in Oakland, California. The foundation works to end childhood hunger, increase access to quality education, and provide safe spaces for children to stay active.


title: Ayesha Curry

text: Her 2014 company "Little Lights of Mine" sold its own brand of extra virgin olive oil, and 10% of all proceeds are donated to the charity No Kid Hungry.


title: Ayesha Curry

text: In 2016, Curry collaborated with chef Michael Mina in "The Mina Test Kitchen of International Smoke", a Bay Area pop-up restaurant. In July 2019, the "Mina/Curry International Smoke" restaurant opened another location at One Paseo in Carmel Valley, San Diego.


title: Ayesha Curry

text: In 2017, Curry started "Homemade," the Oakland-based meal-kit delivery service, turned (in 2019) retail store pop-up.


title: Ayesha Curry

text: In April 2020, Curry launched "Sweet July", a brand consisting of a lifestyle magazine, brick-and-mortar store, and product line. In September 2020, she launched her television and film production company "Sweet July Productions", with a first-look deal at Entertainment One.


title: Ayesha Curry

text: Ayesha is the daughter of John and Carol Alexander (née Chin) and has four siblings: Maria, Janiece, Jaz and Chad. Her mother is of Afro-Jamaican and Chinese-Jamaican descent while her father is of mixed African-American and Polish descent. She was born and raised in Toronto until the age of 14, when she moved to Charlotte, North Carolina. She first gained an interest in cooking at a young age. With her mother operating a salon in the basement of their home, Ayesha would watch as her babysitter cooked Trinidadian curry and roti and brought it down to customers.


title: Ayesha Curry

text: On July 30, 2011, she married NBA player Stephen Curry. The two had met in a church youth group in Charlotte when they were 15 and 14 years old. They did not start dating until years later when Ayesha was pursuing her acting career in Hollywood and Stephen was visiting for an awards show. Ayesha soon moved back to Charlotte close to where Stephen was playing college basketball at Davidson College. Together, they have three children. As of 2019, they reside in Atherton, California.


title: Ayesha Curry

text: Curry is a Christian; of her faith, she said: "It's the foundation for everything that I do, really. … With my relationship with my husband, it's what it's founded on." She added that "[W]hen Steph decided to play basketball, I had the same conversation with him that he had with me. 'Whatever you do, do it well, but do it for God.' I think that's what has kept us grounded. When I started my blog called 'Little Lights of Mine,' my whole goal was to do the things I wanted to do, but all while being a light for Him."


title: Shadow the Hedgehog

text: Within the "Sonic" franchise's fictional universe, Shadow is an artificial, anthropomorphic black hedgehog created by Professor Gerald Robotnik, the grandfather of series antagonist Doctor Eggman. After witnessing the murder of his best friend Maria, Shadow vows to keep his promise to her that he would protect the world from danger. As an antihero, Shadow has good intentions but will do whatever it takes to accomplish his goals, putting him at odds with series protagonist Sonic the Hedgehog, thus serving as one of the eponymous title character's greatest rivals, if not the greatest. Shadow shares many attributes with Sonic and thus controls similarly in games, but is distinguished by his use of vehicles and firearms.


title: Shadow the Hedgehog

text: The idea for Shadow originated during the development of the original "Sonic Adventure", with Iizuka and Maekawa ensuring he would be a subtle, "cool" character players could care about. Although Shadow is one of the series' most popular characters and was named one of the greatest video game characters by "Guinness World Records" in 2011, he has proven divisive among video game journalists. Some have praised his role in "Sonic Adventure 2" and his levels' preservation of the "Sonic" theme, but others have criticized his dark and over-the-top characterization. The "Shadow" game sold well, but received generally unfavorable reviews.


title: Shadow the Hedgehog

text: Shadow is an anthropomorphic black hedgehog appearing in Sega's "Sonic the Hedgehog" series of platform games and its various spin-offs. He first appeared in the 2001 installment "Sonic Adventure 2", the final "Sonic" game released for a Sega Dreamcast. His roles in the games vary. Some, such as the main series games "Sonic Adventure 2", "Sonic Heroes" (2003), and "Sonic the Hedgehog" (2006) feature him as a major playable character, and he is the protagonist of the spin-off "Shadow the Hedgehog" (2005) and a downloadable content (DLC) package for "Sonic Forces" (2017). Others, such as the anniversary game "Sonic Generations" (2011), limit him to a non-playable role.


title: Shadow the Hedgehog

text: In the games, Shadow is depicted as a mysterious, sharp-witted, and brooding antihero. While his ultimate goal is to protect the world from danger, he dislikes humanity, and once he has set a goal, he does whatever it takes to accomplish it. This often causes him to take risks without thinking them through and puts him at odds with series protagonist Sonic the Hedgehog. Although a loner, Shadow collaborates with treasure hunter Rouge the Bat and renegade robot E-123 Omega in games such as "Sonic Heroes", "Sonic the Hedgehog" (2006), and "Sonic Forces". Shadow allies with Sonic in some games, but also does so with Doctor Eggman in "Sonic Adventure 2" and "Shadow the Hedgehog".


title: Shadow the Hedgehog

text: Shadow shares many similarities with Sonic. Visually, "GameSpot" Ben Stahl described Shadow as "an evil version of Sonic himself—similar in appearance, but with darker skin, more angled eyes, and a fearsome snarl instead of Sonic's trademark grin." "GamesRadar+" Justin Leeper said that if Sonic was Superman, then Shadow would be his Batman. The characters control similarly in games, as both share skills and the ability to run at great speeds. Shadow has unique attributes in some games, such as his uses of firearms and vehicles in "Shadow the Hedgehog" and "Sonic the Hedgehog", respectively. He can also use the Chaos Emeralds to perform "Chaos Control"—allowing him to distort time—and create weapons like spears. Like Sonic, Shadow can transform into a "Super" form giving him special powers.


title: Shadow the Hedgehog

text: Shadow was created by Takashi Iizuka and Shiro Maekawa, who respectively served as director and writer of "Sonic Adventure 2". According to Iizuka, the idea for Shadow originated during development of the original "Sonic Adventure", when Sonic Team intended to introduce a rival for Sonic in a potential sequel. Although they rarely discussed the idea, the staff continually thought about it. Eventually, while work on "Sonic Adventure 2" progressed, Sonic Team found use in Shadow when they laid out the game's "good vs. evil" plotlines. Shadow's name at the beginning of development was "Terios" ("reflection of"), referencing his role as Sonic's doppelganger. Sonic Team tasked Maekawa with developing Shadow, whom they wanted to look just as "cool" as Sonic. Maekawa settled on the design of a black hedgehog, but struggled coming up with his personality. One night, while he brainstormed lines for a scene in which Sonic confronts Shadow for impersonating him, Maekawa came up with Shadow's first line: "Hmph, aren't you the fake one here?" As part of shaping his subtle character, Maekawa envisioned Shadow would refer to himself using the more humble Japanese pronoun "boku" (僕). Iizuka made sure that Shadow's introduction also brought new events to the game, as he wanted players to care about the character.


title: Shadow the Hedgehog

text: "Sonic Adventure 2" was intended to be Shadow's only appearance, but his popularity among fans led to him returning in 2003's "Sonic Heroes". Additionally, Sonic Team wanted to feature Shadow in a spin-off game. By 2005, Sonic Team was interested in developing a high-speed shooter game. They chose to focus on Shadow—whom they felt would provide "the perfect venue... to try our hand at this genre"—leading to the development of "Shadow the Hedgehog". Series co-creator Yuji Naka hoped "Shadow" would lead to a spin-off series about the character. When developing Shadow's design and world, Sonic Team was influenced by films such as "Underworld" (2003), "Constantine" (2005), and those in the "Terminator" series. The team abandoned Shadow's shooting gameplay when working on "Sonic the Hedgehog" in 2006. Instead, director Shun Nakamura emphasized combat to differentiate his gameplay from that of Sonic's; while Sonic was designed for speedy platforming, Shadow was designed for fighting enemies. After "Sonic and the Black Knight" (2009), Shadow did not appear as a playable character in a "Sonic" platformer for some time, until the release of "Sonic Forces" in 2017. Nakamura explained that Sonic Team brought Shadow back for "Sonic Forces" so it would appeal to fans of the "Adventure" games, as the character is "extremely popular" among that group. Iizuka has commented that another Shadow-oriented spin-off is a possibility.


title: Shadow the Hedgehog

text: In Japan, Kōji Yusa voices Shadow. The character's English voice actor has changed several times. David Humphrey was the first to assume the role, but was replaced by Jason Griffith, who voiced Shadow and Sonic in the English dub of the anime series "Sonic X" (2003–2006), for "Shadow the Hedgehog" in 2005. Ryan Drummond briefly filled in for David Humphrey as Shadow's voice during the Final Hazard boss level in "Sonic Adventure 2". Kirk Thornton has since voiced Shadow from 2010 onwards, starting with "Sonic Free Riders".


title: Shadow the Hedgehog

text: Within the "Sonic" series' fictional universe, Shadow the Hedgehog is an artificial being created by Professor Gerald Robotnik through genetic engineering as part of an experiment to cure his granddaughter Maria from a deadly illness. While Shadow and Maria formed a strong bond, the government deemed him a threat. Shadow was placed in suspended animation and a military organization, the Guardian Units of Nations (G.U.N.), killed Maria as Shadow tried to protect her. Maria's death traumatized Shadow, who vowed to keep his promise to her that he would protect the world from danger. In "Sonic Adventure 2", Gerald's grandson, Doctor Eggman, learns of Shadow and revives him as part of a plan to conquer the world and defeat Sonic the Hedgehog. Shadow agrees to help Eggman and frames Sonic for their evil deeds. However, Shadow eventually allies himself with Sonic to prevent the world's destruction after he remembers the promise he made to Maria. However, he is unable to handle the power of all seven Chaos Emeralds in a Super state as well as Sonic, and is seen plummeting to the Earth from space after the final boss fight. He is believed to have died in the final battle until "Sonic Heroes"; Rouge the Bat discovers him alive in Eggman's base during a search for "treasure". He remembers nothing except his name and Maria's death, and teams up with Rouge and E-123 Omega to find Eggman and learn of his past. In "Shadow the Hedgehog", Shadow, still experiencing amnesia, becomes caught in a three-way war between Eggman, G.U.N., and the Black Arms, an alien army led by Black Doom. Shadow can choose to help G.U.N., Sonic and his friends, Eggman, or the Black Arms. At the end of the game, Shadow recovers from his amnesia and learns the truth about his past, including that Gerald created him using Black Doom's blood. He chooses to put the past behind him and move on, and in "Sonic the Hedgehog" is depicted as having joined G.U.N.


title: Shadow the Hedgehog

text: Shadow quickly proved popular among players of "Sonic Adventure 2", contributing to his return in later games. Additionally, responses to his introduction were favorable; critics considered his levels in "Sonic Adventure 2" among the game's highlights. "GameSpot" Shane Satterfield wrote Shadow's levels were exciting and helped preserve the general theme of "Sonic" games, and wished they had been more plentiful. "Nintendo Life" Mark Reece similarly felt Shadow's levels successfully adapted the "Sonic" formula to 3D. However, despite strong sales, the 2005 "Shadow" game received generally unfavorable reviews and, according to "Official Nintendo Magazine" Thomas East, tarnished the character's reputation.<ref name="ONM: best/worst"></ref>


title: Shadow the Hedgehog

text: Reviews for "Shadow the Hedgehog" criticized numerous aspects of the character, such as his controls, use of firearms, and characterization. "Game Informer" Matt Helgeson decried Shadow as a character who lacked personality and mocked his "ridiculous" and "laughable" Clint Eastwood rasp, while "GameSpy" Patrick Klepek felt the game was proof the "Sonic" series had jumped the shark. Similarly, "1UP.com" Shane Bettenhausen compared Shadow to Poochie, a character from "The Simpsons" episode "The Itchy & Scratchy & Poochie Show" (1997) symbolic of creating a new character simply to boost a flagging series. Klepek thought guns made sense for Shadow's character but did not have a compelling use in the game, and expressed hope Sonic Team would "[bury] him alongside the same graves as the third-tier of characters from "Knuckles' Chaotix"." Critics reviewing the 2006 "Sonic the Hedgehog" considered Shadow's gameplay slightly better than that of Sonic's but felt it did not add enough to the experience, while "Den of Geek" Chris Freiberg wrote the Shadow DLC for "Sonic Forces" added some replay value to a game he criticized for its short length.


title: Shadow the Hedgehog

text: Writers have called Shadow—both the game and the character—an ill-advised attempt to bring a sense of maturity to the "Sonic" series. Indeed, "IGN" Levi Buchanan and "1UP"s Jeremy Parish considered him one of the series' biggest problems; Parish wrote that of the unnecessary "Sonic" characters Sega should retire, Shadow was the most in need of it. Numerous video game journalists have mockingly described the character as "edgy", Internet slang referring to someone who exhibits disconcerting behavior in an effort to impress others. In 2010, DeviantArt user "cmara" released a webcomic depicting Shadow in a romantic relationship with Shrek, the title character of the DreamWorks film series. According to "Kotaku" Nathan Grayson, the comic paired the two because "if Shrek was the big screen embodiment of nu-millennium toilet garbage, Shadow the Hedgehog—with his hilariously unfitting blend of guns and angst in a colorful world of fast animals in clown shoes—was his video game bride. Both tried to act like they were too cool for 'kid stuff.' Too sophisticated, too edgy. They were made for each other—and approximately one billion people between the ages of 12 and 34."


title: Shadow the Hedgehog

text: Shadow is a divisive "Sonic" character. Some, such as East, who ranked him one of the series' best characters, praise him for his role in "Sonic Adventure 2"; "Game Informer" Brian Shea called Shadow a "fun equal" to Sonic who delivered the series' traditional sense of speed, and "Polygon" Allegra Frank said he is a fan-favorite. "For others," wrote "Kotaku" Mike Fahey, Shadow "signifies the looming death of a beloved series." Fahey felt Shadow's self-titled game was when the "Sonic" franchise lost its identity, and dismissed those who argued in favor of his role in "Sonic Adventure 2". Jim Sterling, writing for "GamesRadar+", ranked Shadow among the series' worst characters, arguing he lost his relevance over time and calling him "the ultimate example of a good idea gone rotten." Brian Shea from "Game Informer" included Shadow in a similar list, whom observed "Shadow's brooding "tortured soul" personality wore on a lot of fans quickly..." In a more positive write-up, "Fanbyte's" Kenneth Shepard argued Shadow's characterization was more complex than most characters in the series, but recent iterations have leaned harder into a one-dimensional "edgelord" archetype. Despite this, in 2005 Naka said Sonic Team had determined Shadow was the series' most popular character excluding Sonic himself, a finding reaffirmed in a 2009 Sega poll. In 2011, "Guinness World Records" named Shadow among the 50 greatest video game characters of all time.


title: Shadow the Hedgehog

text: Outside the video game series, Shadow appears in the anime series "Sonic X", which adapts the story of the "Sonic Adventure" games. The original Japanese cast from the games reprised their voice roles for the game, while Jason Griffith voiced Shadow in the English dub by 4Kids Entertainment. In the "Sonic Boom" (2014–2017) spin-off franchise, Shadow appears in the 2014 games "" for the Wii U and "" for the Nintendo 3DS, and the episodes "It Takes a Village to Defeat a Hedgehog" and both parts entitled "Eggman: The Video Game", voiced by Kirk Thornton. He also appears in the "Sonic the Hedgehog" comic books published by Archie Comics and IDW Publishing, and his likeness has been used in "Sonic" merchandise. Shadow made his live-action debut in a non-speaking cameo appearance in the mid-credits scene of the 2022 film "Sonic the Hedgehog 2".


title: History of English

text: English is a West Germanic language that originated from Ingvaeonic languages brought to Britain in the mid-5th to 7th centuries AD by Anglo-Saxon migrants from what is now northwest Germany, southern Denmark and the Netherlands. The Anglo-Saxons settled in the British Isles from the mid-5th century and came to dominate the bulk of southern Great Britain. Their language originated as a group of Ingvaeonic languages which were spoken by the settlers in England and southern and eastern Scotland in the early Middle Ages, displacing the Celtic languages (and, possibly, British Latin) that had previously been dominant. Old English reflected the varied origins of the Anglo-Saxon kingdoms established in different parts of Britain. The Late West Saxon dialect eventually became dominant. A significant subsequent influence on the shaping of Old English came from contact with the North Germanic languages spoken by the Scandinavian Vikings who conquered and colonized parts of Britain during the 8th and 9th centuries, which led to much lexical borrowing and grammatical simplification. The Anglian dialects had a greater influence on Middle English.


title: History of English

text: After the Norman conquest in 1066, Old English was replaced, for a time, by Anglo-Norman (also known as Anglo-Norman French) as the language of the upper classes. This is regarded as marking the end of the Old English or Anglo-Saxon era, as during this period the English language was heavily influenced by Anglo-Norman, developing into a phase known now as Middle English. The conquering Normans spoke a Romance langue d'oïl called Old Norman, which in Britain developed into Anglo-Norman. Many Norman and French loanwords entered the local language in this period, especially in vocabulary related to the church, the court system and the government. As Normans are descendants of Vikings who invaded France, Norman French was influenced by Old Norse, and many Norse loanwords in English came directly from French. Middle English was spoken to the late 15th century. The system of orthography that was established during the Middle English period is largely still in use today. Later changes in pronunciation, however, combined with the adoption of various foreign spellings, mean that the spelling of modern English words appears highly irregular.


title: History of English

text: Early Modern English – the language used by William Shakespeare – is dated from around 1500. It incorporated many Renaissance-era loans from Latin and Ancient Greek, as well as borrowings from other European languages, including French, German and Dutch. Significant pronunciation changes in this period included the ongoing Great Vowel Shift, which affected the qualities of most long vowels. Modern English proper, similar in most respects to that spoken today, was in place by the late 17th century.


title: History of English

text: English as we know it today came to be exported to other parts of the world through British colonisation, and is now the dominant language in Britain and Ireland, the United States and Canada, Australia, New Zealand and many smaller former colonies, as well as being widely spoken in India, parts of Africa, and elsewhere. Partially due to influence of the United States and its globalized efforts of commerce and technology, English took on the status of a global lingua franca in the second half of the 20th century. This is especially true in Europe, where English has largely taken over the former roles of French and (much earlier) Latin as a common language used to conduct business and diplomacy, share scientific and technological information, and otherwise communicate across national boundaries. The efforts of English-speaking Christian missionaries have resulted in English becoming a second language for many other groups.


title: History of English

text: English has its roots in the languages of the Germanic peoples of northern Europe. During the Roman Empire, most of the Germanic-inhabited area (Germania) remained independent from Rome, although some southwestern parts were within the empire. Some Germanics served in the Roman military, and troops from Germanic tribes such as the Tungri, Batavi, Menapii and Frisii served in Britain (Britannia) under Roman command. Germanic settlement and power expanded during the Migration Period, which saw the fall of the Western Roman Empire. A Germanic settlement of Britain took place from the 5th to the 7th century, following the end of Roman rule on the island. The "Anglo-Saxon Chronicle" relates that around the year 449 Vortigern, king of the Britons, invited the "Angle kin" (Angles allegedly led by the Germanic brothers Hengist and Horsa) to help repel invading Picts, in return for lands in the southeast of Britain. This led to waves of settlers who eventually established seven kingdoms, known as the heptarchy. (The "Chronicle" was not a contemporaneous work, however, and cannot be regarded as an accurate record of such early events.) Bede, who wrote his "Ecclesiastical History" in AD 731, writes of invasion by Angles, Saxons and Jutes, although the precise nature of the invasion and settlement and the contributions made by these particular groups are the subject of much dispute among historians.


title: History of English

text: The languages spoken by the Germanic peoples who initially settled in Britain were part of the West Germanic branch of the Germanic language family. They consisted of dialects from the Ingvaeonic grouping, spoken mainly around the North Sea coast, in regions that lie within modern Denmark, north-west Germany and the Netherlands. Due to specific similarities between early English and Old Frisian, an Anglo-Frisian grouping is also identified, although it does not represent a node in the family tree.


title: History of English

text: These dialects had most of the typical West Germanic features, including a significant amount of grammatical inflection. Vocabulary came largely from the core Germanic stock, although due to the Germanic peoples' extensive contacts with the Roman world, the settlers' languages already included a number of loanwords from Latin. For instance, the predecessor of Modern English "wine" had been borrowed into early Germanic from the Latin "vinum".


title: History of English

text: The Germanic settlers in the British Isles initially spoke a number of different dialects, which would develop into a language that came to be called Anglo-Saxon. It displaced the indigenous Brittonic Celtic (and the Latin of the former Roman rulers) in parts of the areas of Britain that later formed the Kingdom of England, while Celtic languages remained in most of Scotland, Wales and Cornwall, and many compound Celtic-Germanic place names survive, hinting at early language mixing. Old English continued to exhibit local variation, the remnants of which continue to be found in dialects of Modern English. The four main dialects were Mercian, Northumbrian, Kentish and West Saxon; the last of these formed the basis for the literary standard of the later Old English period, although the dominant forms of Middle and Modern English would develop mainly from Mercian.


title: History of English

text: Old English was first written using a runic script called the futhorc, but this was replaced by a version of the Latin alphabet introduced by Irish missionaries in the 8th century. Most literary output was in either the Early West Saxon of Alfred the Great's time, or the Late West Saxon (regarded as the "classical" form of Old English) of the Winchester school inspired by Bishop Æthelwold of Winchester and followed by such writers as the prolific Ælfric of Eynsham ("the Grammarian"). The most famous surviving work from the Old English period is the epic poem "Beowulf", composed by an unknown poet.


title: History of English

text: The introduction of Christianity from around the year 600 encouraged the addition of over 400 Latin loan words into Old English, such as the predecessors of the modern "priest", "paper", and "school", and a smaller number of Greek loan words. The speech of eastern and northern parts of England was also subject to strong Old Norse influence due to Scandinavian rule and settlement beginning in the 9th century (see below).


title: History of English

text: Most native English speakers today find Old English unintelligible, even though about half of the most commonly used words in Modern English have Old English roots. The grammar of Old English was much more inflected than modern English, combined with freer word order, and was grammatically quite similar in some respects to modern German. The language had demonstrative pronouns (equivalent to "this" and "that") but did not have the definite article "the". The Old English period is considered to have evolved into the Middle English period some time after the Norman conquest of 1066, when the language came to be influenced significantly by the new ruling class's language, Old Norman.


title: History of English

text: Vikings from modern-day Norway and Denmark began to raid parts of Britain from the late 8th century onward. In 865, however, a major invasion was launched by what the Anglo-Saxons called the Great Heathen Army, which eventually brought large parts of northern and eastern England (the Danelaw) under Scandinavian control. Most of these areas were retaken by the English under Edward the Elder in the early 10th century, although York and Northumbria were not permanently regained until the death of Eric Bloodaxe in 954. Scandinavian raids resumed in the late 10th century during the reign of Æthelred the Unready, and Sweyn Forkbeard eventually succeeded in briefly being declared king of England in 1013, followed by the longer reign of his son Cnut from 1016 to 1035, and Cnut's sons Harold Harefoot and Harthacnut until 1042.


title: History of English

text: The Scandinavians, or Norsemen, spoke dialects of a North Germanic language known as Old Norse. The Anglo-Saxons and the Scandinavians thus spoke related languages from different branches (West and North) of the Germanic family; many of their lexical roots were the same or similar, although their grammatical systems were more divergent. It is likely that significant numbers of Norse speakers settled in the Danelaw during the period of Scandinavian control. Many place-names in those areas are of Scandinavian provenance (those ending in "-by", for example); it is believed that the settlers often established new communities in places that had not previously been developed by the Anglo-Saxons. The extensive contact between Old English and Old Norse speakers, including the possibility of intermarriage that resulted from the acceptance of Christianity by the Danes in 878, undoubtedly influenced the varieties of those languages spoken in the areas of contact. Some scholars even believe that Old English and Old Norse underwent a kind of fusion and that the resulting English language might be described as a mixed language or creole. During the rule of Cnut and other Danish kings in the first half of the 11th century, a kind of diglossia may have come about, with the West Saxon literary language existing alongside the Norse-influenced Midland dialect of English, which could have served as a koine or spoken lingua franca. When Danish rule ended, and particularly after the Norman Conquest, the status of the minority Norse language presumably declined relative to that of English, and its remaining speakers assimilated to English in a process involving language shift and language death. The widespread bilingualism that must have existed during the process possibly contributed to the rate of borrowings from Norse into English.


title: History of English

text: Only about 100 or 150 Norse words, mainly connected with government and administration, are found in Old English writing. The borrowing of words of this type was stimulated by Scandinavian rule in the Danelaw and during the later reign of Cnut. However, most surviving Old English texts are based on the West Saxon standard that developed outside the Danelaw; it is not clear to what extent Norse influenced the forms of the language spoken in eastern and northern England at that time. Later texts from the Middle English era, now based on an eastern Midland rather than a Wessex standard, reflect the significant impact that Norse had on the language. In all, English borrowed about 2000 words from Old Norse, several hundred surviving in Modern English.


title: History of English

text: Norse borrowings include many very common words, such as "anger", "bag", "both", "hit", "law", "leg", "same", "skill", "sky", "take", "window", and even the pronoun "they". Norse influence is also believed to have reinforced the adoption of the plural copular verb form "are" rather than alternative Old English forms like "sind". It is also considered to have stimulated and accelerated the morphological simplification found in Middle English, such as the loss of grammatical gender and explicitly marked case (except in pronouns). That is possibly confirmed by observations that simplification of the case endings occurred earliest in the north and latest in the southwest. The spread of phrasal verbs in English is another grammatical development to which Norse may have contributed (although here a possible Celtic influence is also noted).


title: History of English

text: Some scholars have claimed that Old English died out entirely and was replaced by Norse towards the end of the Old English period and as part of the transition to Middle English, by virtue of the Middle English syntax being much more akin to Norse than Old English. Other scholars reject this claim.


title: History of English

text: Middle English is the form of English spoken roughly from the time of the Norman Conquest in 1066 until the end of the 15th century.


title: History of English

text: For centuries after the Conquest, the Norman kings and high-ranking nobles in England and to some extent elsewhere in the British Isles spoke Anglo-Norman, a variety of Old Norman, originating from a northern langue d'oïl dialect. Merchants and lower-ranked nobles were often bilingual in Anglo-Norman and English, whilst English continued to be the language of the common people. Middle English was influenced by both Anglo-Norman, and later Anglo-French (see characteristics of the Anglo-Norman language).


title: History of English

text: Until the 14th century, Anglo-Norman and then French were the language of the courts and government. Even after the decline of Norman, standard French retained the status of a formal or prestige language, and about 10,000 French (and Norman) loan words entered Middle English, particularly terms associated with government, church, law, the military, fashion, and food (see English language word origins and List of English words of French origin). The strong influence of Old Norse on English (described in the previous section) also becomes apparent during this period. The impact of the native British Celtic languages that English continued to displace is generally held to be very small, although a few scholars have attributed some grammatical forms, such as periphrastic "do", to Celtic influence. These theories have been criticized by a number of other linguists. Some scholars have also put forward hypotheses that Middle English was a kind of creole language resulting from contact between Old English and either Old Norse or Anglo-Norman.


title: History of English

text: English literature began to reappear after 1200, when a changing political climate and the decline in Anglo-Norman made it more respectable. The Provisions of Oxford, released in 1258, was the first English government document to be published in the English language after the Norman Conquest. In 1362, Edward III became the first king to address Parliament in English. The Pleading in English Act 1362 made English the only language in which court proceedings could be held, though the official record remained in Latin. By the end of the century, even the royal court had switched to English. Anglo-Norman remained in use in limited circles somewhat longer, but it had ceased to be a living language. Official documents began to be produced regularly in English during the 15th century. Geoffrey Chaucer, who lived in the late 14th century, is the most famous writer from the Middle English period, and "The Canterbury Tales" is his best-known work.


title: History of English

text: The English language changed enormously during the Middle English period, in vocabulary, in pronunciation, and in grammar. While Old English is a heavily inflected language (synthetic), the use of grammatical endings diminished in Middle English (analytic). Grammar distinctions were lost as many noun and adjective endings were levelled to "-e". The older plural noun marker "-en" (retained in a few cases such as "children" and "oxen") largely gave way to "-s", and grammatical gender was discarded. Definite article "þe" appears around 1200, later spelled as "the", first appearing in East and North England as a substitute for Old English "se" and "seo", nominative forms of "that."


title: History of English

text: English spelling was also influenced by Norman in this period, with the and sounds being spelled "th" rather than with the Old English letters þ (thorn) and ð (eth), which did not exist in Norman. These letters remain in the modern Icelandic and Faroese alphabets, having been borrowed from Old English via Old West Norse.


title: History of English

text: English underwent extensive sound changes during the 15th century, while its spelling conventions remained largely constant. Modern English is often dated from the Great Vowel Shift, which took place mainly during the 15th century. The language was further transformed by the spread of a standardized London-based dialect in government and administration and by the standardizing effect of printing, which also tended to regularize capitalization. As a result, the language acquired self-conscious terms such as "accent" and "dialect". As most early presses came from continental Europe, a few native English letters such as þ and ð died out; for some time "þe" was written as "ye." By the time of William Shakespeare (mid 16th - early 17th century), the language had become clearly recognizable as Modern English. In 1604, the first English dictionary was published, "A Table Alphabeticall".


title: History of English

text: Increased literacy and travel facilitated the adoption of many foreign words, especially borrowings from Latin and Greek, often terms for abstract concepts not available in English. In the 17th century, Latin words were often used with their original inflections, but these eventually disappeared. As there are many words from different languages and English spelling is variable, the risk of mispronunciation is high, but remnants of the older forms remain in a few regional dialects, most notably in the West Country. During the period, loan words were borrowed from Italian, German, and Yiddish. British acceptance of and resistance to Americanisms began during this period.


title: History of English

text: The first authoritative and full-featured English dictionary, the "Dictionary of the English Language", was published by Samuel Johnson in 1755. To a high degree, the dictionary standardized both English spelling and word usage. Meanwhile, grammar texts by Lowth, Murray, Priestly, and others attempted to prescribe standard usage even further.


title: History of English

text: Early Modern English and Late Modern English, also called Present-Day English (PDE), differ essentially in vocabulary. Late Modern English has many more words, arising from the Industrial Revolution and technologies that created a need for new words, as well as international development of the language. The British Empire at its height covered one quarter of the Earth's land surface, and the English language adopted foreign words from many countries. British English and North American English, the two major varieties of the language, are together spoken by 400 million people. The total number of English speakers worldwide may exceed one billion. The English language will almost certainly continue to evolve over time. With the development of computer and online environments (such as chat rooms, social media expressions, and apps), and the adoption of English as a worldwide lingua franca across cultures, customs, and traditions, it should not be surprising to see further shortening of words, phrases, and/or sentences.


title: History of English

text: Over the last 1,200 years or so, English has undergone extensive changes in its vowel system, but many fewer changes to its consonants.


title: History of English

text: In the Old English period, a number of umlaut processes affected vowels in complex ways, and unstressed vowels were gradually eroded, eventually leading to a loss of grammatical case and grammatical gender in the Early Middle English period. The most important umlaut process was *i-mutation (c. 500 CE), which led to pervasive alternations of all sorts, many of which survive in the modern language: e.g. in noun paradigms ("foot" vs. "feet", "mouse" vs. "mice", "brother" vs. "brethren"); in verb paradigms ("sold" vs. "sell"); nominal derivatives from adjectives ("strong" vs. "strength", "broad" vs. "breadth", "foul" vs. "filth") and from other nouns ("fox" vs. "vixen"); verbal derivatives ("food" vs. "to feed"); and comparative adjectives ("old" vs. "elder"). Consonants were more stable, although velar consonants were significantly modified by palatalization, which produced alternations such as "speak" vs. "speech", "drink" vs. "drench", "wake" vs. "watch", "bake" vs. "batch".


title: History of English

text: The Middle English period saw further vowel changes. Most significant was the Great Vowel Shift (c. 1500 CE), which transformed the pronunciation of all long vowels. This occurred after the spelling system was fixed, and accounts for the drastic differences in pronunciation between "short" "mat, met, bit, cot" vs. "long" "mate, mete/meet, bite, coat". Other changes that left echoes in the modern language were homorganic lengthening before "ld", "mb", "nd", which accounts for the long vowels in "child", "mind", "climb", etc.; pre-cluster shortening, which resulted in the vowel alternations in "child" vs. "children", "keep" vs. "kept", "meet" vs. "met"; and trisyllabic laxing, which is responsible for alternations such as "grateful" vs. "gratitude", "divine" vs. "divinity", "sole" vs. "solitary".


title: History of English

text: Among the more significant recent changes to the language have been the development of rhotic and non-rhotic accents (i.e. "r-dropping"); the trap-bath split in many dialects of British English; and flapping of "t" and "d" between vowels in American English and Australian English.


title: History of English

text: The following table shows the principal developments in the stressed vowels, from Old English through Modern English ("C" indicates any consonant):


title: History of English

text: The following chart shows the primary developments of English vowels in the last 600 years, in more detail, since Late Middle English of Chaucer's time. The Great Vowel Shift can be seen in the dramatic developments from c. 1400 to 1600.


title: History of English

text: Neither of the above tables covers the history of Middle English diphthongs, the changes before /r/, or various special cases and exceptions. For details, see phonological history of English as well as the articles on Old English phonology and Middle English phonology/.


title: History of English

text: The vowel changes over time can be seen in the following example words, showing the changes in their form over the last 2,000 years:


title: History of English

text: The English language once had an extensive declension system similar to Latin, Greek, modern German and Icelandic. Old English distinguished among the nominative, accusative, dative, and genitive cases, and for strongly declined adjectives and some pronouns also a separate instrumental case (which otherwise and later completely coincided with the dative). In addition, the dual number was distinguished from the singular and plural.


title: History of English

text: Declension was greatly simplified during the Middle English period, when the accusative and dative cases of the pronouns merged into a single oblique case that also replaced the genitive case after prepositions. Nouns in Modern English no longer decline for case, except for the genitive.


title: History of English

text: Pronouns such as "whom" and "him" (contrasted with "who" and "he"), are a conflation of the old accusative and dative cases, as well as of the genitive case after prepositions (while "her" also includes the genitive case). This conflated form is called the "oblique case" or the "object (objective) case", because it is used for objects of verbs (direct, indirect, or oblique) as well as for objects of prepositions. (See object pronoun.) The information formerly conveyed by distinct case forms is now mostly provided by prepositions and word order. In Old English as well as modern German and Icelandic as further examples, these cases had distinct forms.


title: History of English

text: Although some grammarians continue to use the traditional terms "accusative" and "dative", these are functions rather than morphological cases in Modern English. That is, the form "whom" may play accusative or dative roles (as well as instrumental or prepositional roles), but it is a single morphological form, contrasting with nominative "who" and genitive "whose". Many grammarians use the labels "subjective", "objective", and "possessive" for nominative, oblique, and genitive pronouns.


title: History of English

text: Modern English nouns exhibit only one inflection of the reference form: the possessive case, which some linguists argue is not a case at all, but a clitic (see the entry for genitive case for more information).


title: History of English

text: "Beowulf" is an Old English epic poem in alliterative verse. It is dated from the 8th to the early 11th centuries. These are the first 11 lines: