Root primordia (brown spots) as seen on the butt of a freshly cut pineapple crown intended for vegetative reproduction. A primordium (; plural: primordia; synonym: anlage) in embryology, is an organ or tissue in its earliest recognizable stage of development.MedicineNet.com Cells of the primordium are called primordial cells. A primordium is the simplest set of cells capable of triggering growth of the would-be organ and the initial foundation from which an organ is able to grow.
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The mammary ridge or mammary crest is a primordium specific for the development of the mammary gland.
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Histodifferentiation is the differentiation of different tissue types during the development of an embryo/ undifferentiated group of cells. Furthermore, morphogenesis is a predominant physiological process during the cap stage. This is due to formation of primordium of the tooth. The primordium contains each of the primordial tissue types, essential for the development of successive teeth.
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At 21 °C, luminescence persists for about 3 days, and becomes undetectable to the naked eyes about 72 hours after primordium initiation.
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Indeed, at the end of stage II, scutellum, coleoptile, coleorhiza, primary root primordium, and leaf primordia have already been reported to be present.
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The similarity in cortical gene expression in Emx2 mutants and mice in which the anterior FGF8 source is augmented suggests that FGF8 controls the graded expression (low anterior, high posterior) of Emx2 in the cortical primordium. Emx2 is one of the protomap molecular determinants that prove to be closely interacted with Pax6. Emx2 and Pax6 are expressed in opposing gradients along the A/P axis of the cortical primordium and cooperate to set up area pattern.
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Leaf primordia are initiated by the suppression of the genes and proteins of class I KNOX family (such as SHOOT APICAL MERISTEMLESS). These class I KNOX proteins directly suppress gibberellin biosynthesis in the leaf primordium. Many genetic factors were found to be involved in the suppression of these class I KNOX genes in leaf primordia (such as ASYMMETRIC LEAVES1, BLADE-ON- PETIOLE1, SAWTOOTH1, etc.). Thus, with this suppression, the levels of gibberellin increase and leaf primordium initiate growth.
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This duct is known as the pronephric duct, mesonephric duct or Wolffian duct. While this transient primordium never forms functional nephrons, the duct derived from it is essential to the development of the more complex later kidneys.
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Guilty Spark appears in the novels Halo: The Flood, the Forerunner Saga series of novels, and Halo: Renegades. The character's voice actor, Tim Dadabo, serves as the narrator of the audiobook edition of Halo: Primordium, the second novel in The Forerunner Saga by Greg Bear. In Primordium, he is rescued by the salvage crew of the Ace of Spades after crashing on an isolated planet. It is eventually revealed that he was originally a human being named Chakas who was digitized by the Forerunners at the expense of his biological form.
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Amanita jacksonii buttons emerging from their universal veils gills of Lactarius indigo, a milk-cap mushroom A mushroom develops from a nodule, or pinhead, less than two millimeters in diameter, called a primordium, which is typically found on or near the surface of the substrate. It is formed within the mycelium, the mass of threadlike hyphae that make up the fungus. The primordium enlarges into a roundish structure of interwoven hyphae roughly resembling an egg, called a "button". The button has a cottony roll of mycelium, the universal veil, that surrounds the developing fruit body.
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The genetics behind leaf shape development in Arabidopsis thaliana has been broken down into three stages: The initiation of the leaf primordium, the establishment of dorsiventrality, and the development of a marginal meristem. Leaf primordium is initiated by the suppression of the genes and proteins of the class I KNOX family (such as SHOOT APICAL MERISTEMLESS). These class I KNOX proteins directly suppress gibberellin biosynthesis in the leaf primodium. Many genetic factors were found to be involved in the suppression of these genes in leaf primordia (such as ASYMMETRIC LEAVES1, BLADE-ON-PETIOLE1, SAWTOOTH1, etc.).
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The first cells generated from the cerebellar primordium form a cap over a diamond-shaped cavity of the developing brain called the fourth ventricle forming the two cerebellar hemispheres. The Purkinje cells that develop later are those of the cerebellum´s center-lying section called the vermis. They develop in the cerebellar primordium that covers the fourth ventricle and below a fissure-like region called the isthmus of the developing brain. Purkinje cells migrate toward the outer surface of the cerebellar cortex and form the Purkinje cell layer.
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Bessette et al. (2009), pp. 257–58. The fruit body formation of L. torminosus is pileostipitocarpic. In this type of development, the hymenium forms early on the underside of the cap and upper stem of the mushroom primordium.
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Towards the end of the last stage the larva develops a large sack like structure, a primordium, and begins searching for a suitable surface on which to settle. After settling to the bottom, the larva developss into a juvenile sea star.
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Spirals on a sunflower Detail of Aeonium tabuliforme showing the multiple spiral arrangement (parastichy) Parastichy, in phyllotaxy, is the spiral pattern of the areoles on some plants, such as cacti, sunflowers and pine cones. These spirals involve the insertion of a single primordium.
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The ontogeny, or development, of Mycena stylobates fruit bodies has been investigated in detail using light microscopy and scanning electron microscopy. According to Volker Walther and colleagues, the development can be divided into two phases: in the first, the primordium is established that contains all the structures of the mature fruit body; in the second stage, the primordial stipe elongates rapidly, and the newly exposed hymenium immediately begins spore production. The first detected stage of fruit body formation was an irregularly arranged hyphal structure within the colonized substrate. After rupturing the surface of the substrate and establishing itself there, the structure develops a layer of wrapping hyphae that covers the entire primordium.
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The abductor digit minimi develops at an early stage from an ulnar muscle primordium of the superficial layer of the original undifferentiated mesenchyme of the hand, together with the flexor digitorum superficialis (medial primordia) and the abductor pollicis brevis (radial). In contrast, the remaining hypothenar muscles are derived from the deep layer at a later stage.
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At the genetic level, developmental studies have shown that repression of the KNOX genes is required for initiation of the leaf primordium. This is brought about by ARP genes, which encode transcription factors. Genes of this type have been found in many plants studied till now, and the mechanism i.e. repression of KNOX genes in leaf primordia, seems to be quite conserved.
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The pronephros is the first in a sequence of kidneys that form in vertebrate embryos. The pronephric primordium develops from the intermediate mesoderm, lying between the paraxial (somitic) mesoderm and the lateral plate. In many organisms (e.g. amphibians) this primodium forms anteriorly then migrates posteriorly to fuse with the cloaca, while in others it forms along the length of the intermediate mesoderm.
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Mammalian embryonic research has detailed the neurogenic origins of Purkinje cells . During early development Purkinje cells arise in the ventricular zone in the neural tube, the nervous system´s precursor in the embryo. All cerebellar neurons derive from germinal neuroepithelia from the ventricular zone . Purkinje cells are specifically generated from progenitors in the ventricular neuroepithelium of the embryonic cerebellar primordium .
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Once the more complex mesonephros forms the pronephros undergoes apoptosis in amphibians. In fishes the nephron degenerates but the organ remains and becomes a component of the immune system. In mammals a functional pronephros, in the context of an organ performing waste excretion or osmoregulation, does not develop. However, a kidney primordium that runs along the intermediate mesoderm does form and links up to the cloaca.
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Primophaps schoddei is an extinct genus and species of bird in the pigeon family. It was described from Late Oligocene material (a fossil left coracoid) found at Riversleigh in north-western Queensland, Australia. It was closely related to the Australian bronzewing pigeons, especially those in the genus Phaps. The genus name comes from the Latin primordium, (“beginning” or “origin”), and the Greek phaps (“pigeon”).
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The mushroom's spores are white in deposit, smooth, and ellipsoid-shaped with dimensions of 6–10 by 3.5–4.5 μm. In the development of the fruit body, the preliminary stipe and cap structures appear at the same time within the primordium, and hyphae originating from the stipe form a cover over the developing structures. The mycelia of the mushroom is believed to have bioluminescent properties.
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Formation of the mating tube, initiated by the pheromones A-10 and a-13, is similar to the process of bud emergence during bipolar budding in yeasts. Tremerogen A-10 has been purified and its chemical structure found to be S-polyisoprenyl peptide. Fruit bodies arise from a primordium located beneath the wood bark, and sometimes more than one fruit body can originate separately from the same primordia.
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Pelvic digits may be located at any level of the pelvis, the lower ribs, or even the anterior abdominal wall. It is theorized that pelvic digit anomalies arise during the mesenchymal stage of bone growth, within the first six weeks of embryogenesis. Their formation may result from a failure of the primordium of the coccyx to fuse to the vertebral column, leading to the independent development of a proto-rib structure.
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Illyria is one of the legendary Old Ones, original pure demons from the Primordium Age who ruled territory including modern-day California. She was one of the most feared of all the Old Ones, and ruled from her citadel, Vahla ha'nesh, which corresponds to modern-day Los Angeles. Illyria was eventually defeated and murdered by her many rivals. Illyria in her true form, standing before her demon army.
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The paramesonephric ducts are formed by the craniocaudal invagination of a ribbon of thickened coelomic epithelium that extends from the third thoracic segment caudally to the posterior wall of the urogenital sinus. The caudal parts of the paramesonephric ducts fuse into a single tube, known as the uterovaginal primordium, before flowing into the dorsal aspect of the urogenital sinus at the sinus tubercle directly medial to the mesonephric ducts.
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It has been suggested that embryos with a higher expression of Dmrt1 expression develop into males while embryos with a lower expression are led to female development. In the mouse gonadal primordium, the genital ridge, which forms from intermediate mesoderm, becomes morphologically distinct at E10.5. By E12, sexual differentiation of the gonad is apparent, indicating that genes involved in the formation of the bipotential gonad is expressed before E10.5 and E12.
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The Forerunner Saga is a trilogy of science fiction novels by Greg Bear, based on the Halo series of video games. The books in the series are Halo: Cryptum (2011), Primordium (2012), and Silentium (2013). The books were released in hardcover, e-book, paperback, and audiobook. Bear was given little restriction on the story of the novel; the Halo universe had not yet been explored in that time period.
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The lateral bud primordium (from which the lateral bud develops) is located below SAM. The shoot tip rising from the SAM inhibits the growth of the lateral bud by repressing auxin. When the shoot is cut off, the lateral bud begins to lengthen which is mediated by a release of cytokinin. Once the apical dominance has been lifted from the plant, elongation and lateral growth is promoted and the lateral buds grow into new branches.
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The nematocyst forms through a multi-step assembly process from a giant post-Golgi vacuole. Vesicles from the Golgi apparatus first fuse onto a primary vesicle: the capsule primordium. Subsequent vesicle fusion enables the formation of a tubule outside of the capsule, which then invaginates into the capsule. Then, an early maturation phase enables the formation of long arrays of barbed spines onto the invaginated tubule through the condensation of spinalin proteins.
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Primordium is told through flashbacks, with a damaged Forerunner AI recovered by a human crew. This Forerunner AI, 343 Guilty Spark, was once the human Chakas, and relates his tale through flashbacks. After Chakas, Riser, Bornstellar, and the Didact were taken prisoner by The Master Builder, Chakas and Riser ended up on the Halo ring known as Installation 07. Chakas is also carrying the imprint of Forthencho, a human general during the Human-Forerunner war.
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Halo: Primordium was on the New York Times Bestseller List: Hardcover Fiction for the week of January 7, 2012 at number seventeen. The Los Angeles Times had the book on its Bestseller List for two weeks, at number 16 and then at number 14 for the weeks of January 22 and January 29. Publishers Weekly listed the book at number seventeen on their Bestsellers Hardcover Fiction for the week of January 16, 2012.
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At this time, the medial nasal processes migrate towards each other and fuse forming the primordium of the bridge of the nose and the septum. The migration is helped by the increased growth of the maxillary prominences medially, which compresses the medial nasal processes towards the midline. Their merging takes place at the surface, and also at a deeper level. The merge forms the intermaxillary segment, and this is continuous with the rostral part of the nasal septum.
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The tongue develops after the thyroid primordium so the foramen cecum becomes buried at the base of the tongue. The thyroglossal duct then continues through the neck and lies anterior to the laryngeal cartilage. The duct then passes anteriorly to the developing hyoid bone; however, as the bone continues to grow it can continue to grow posteriorly, become anterior, or even grow to surround the duct. The duct is found very close to the medial line of the neck.
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During the third week of development, the thyroid gland begins to develop from the floor of the pharynx. This primordium begins as an evagination between the first and second pharyngeal grooves, relatively where the anterior two-thirds of the tongue ends. This area is known as the foramen cecum and marks the origin of the thyroglossal duct. As the developing thyroid begins to travel to its intended destination, it remains connected to the tongue via the thyroglossal duct.
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Vegetables usually grow into an unusual shape due to environmental conditions. Damage to one part of the vegetable can cause the growth to slow in that area while the rest grows at the normal rate. When a root vegetable is growing and the tip is damaged, it can sometimes split, forming multiple roots attached at one point. If a plant is in the primordium (embryonic development) stage, damage to the growing vegetable can cause more extreme mutations.
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Before a flower can be produced the plant must undergo floral induction and initiation. Floral induction involves physiological processes in the plant that result in the shoot apical meristem becoming competent to develop flowers. It involves biochemical changes at the apex, particularly those caused by cytokinins and the processes can be reversed. Floral initiation is the morphological transformation of an induced growing point from a vegetative to a floral primordium and involves the plant hormone florigen.
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Mutations in LFY, AP1, and similar promoting genes can cause conversion of flowers into shoots. In contrast to LEAFY, genes like terminal flower (TFL) support the activity of an inhibitor that prevents flowers from growing on the inflorescence apex (flower primordium initiation), maintaining inflorescence meristem identity. Both types of genes help shape flower development in accordance with the ABC model of flower development. Studies have been recently conducted or are ongoing for homologs of these genes in other flower species.
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The labrum is innervated in crustaceans and insects from the tritocerebrum (the back of the brain). However, in development, its embryonic primordium often appears at the anterior of the head and migrates backwards towards its adult position. Furthermore, it often appears as a bilobed structure, with a set of muscles, nerves and gene expression in many ways similar to that of an appendage. This evidence has been used to suggest that the labrum is in fact a highly reduced appendage.
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Very few studies used gonocytes to also refer to the female germ cells in the ovarium primordium. The specification of gonocytes to be confined to male germ cells occurred after foundational differences between the mechanisms of male and female fetal germ cells were uncovered. Some scientists prefer the terms “prospermatogonia” and “prespermatogonia” for their functional clarity. Later studies found that the process from primordial germ cell to spermatogonial development is gradual, without clear gene expression markers to distinguish the precursor cells.
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In Zoonomia, Erasmus Darwin advocated the inheritance of acquired characteristics. He stated, "[F]rom their first rudiment, or primordium, to the termination of their lives, all animals undergo perpetual transformations; which are in part produced by their own exertions in consequence of their desires and aversions, of their pleasures and their pains, or of irritations, or of associations; and many of these acquired forms or propensities are transmitted to their posterity." This statement was similar to Lamarck's ideas on evolution.Zirkle, Conway. (1935).
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In typical prenatal development, sex organs originate from a common primordium during early gestation and differentiate into male or female sexes. The SRY gene, usually located on the Y chromosome and encoding the testis determining factor, determines the direction of this differentiation. The absence of it allows the gonads to continue to develop into ovaries. Thereafter, the development of the internal, and external reproductive organs is determined by hormones produced by certain fetal gonads (ovaries or testes) and the cells' response to them.
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Once the leaf primordial cells are established from the SAM cells, the new axes for leaf growth are defined, one important (and more studied) among them being the abaxial-adaxial (lower-upper surface) axes. The genes involved in defining this, and the other axes seem to be more or less conserved among higher plants. Proteins of the HD-ZIPIII family have been implicated in defining the adaxial identity. These proteins deviate some cells in the leaf primordium from the default abaxial state, and make them adaxial.
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Pioneer neurons are born in the ventricular neuroepithelium all over the cortical primordium. In the rat cortex, they appear at embryonic day (E) 11.5 in the lateral aspect of the telencephalic vesicle and cover its whole surface on E12. These cells, which show intense immunoreactivity for calbindin and calretinin, are characterized by their large size and axonal projection. They remain in the marginal zone after the formation of the cortical plate; they project first into the ventricular zone, and then into the subplate and the internal capsule.
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At about the 7th week in utero, the dental lamina is produced, and it serves as the primordium for the ectodermal portion of the deciduous teeth. Later during the development of the jaws, permanent molars arise directly from the distal extension of the dental lamina. The vestibular lamina is the thickening of oral epithelium in a facial or buccal direction from the dental lamina. Meanwhile, a cleft will form a groove that becomes the area of the mucobuccal or mucolabial fold in the future vestibule.
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The members of the MADS-box family of transcription factors play a very important and evolutionarily conserved role in flower development. According to the ABC model of flower development, three zones - A, B and C - are generated within the developing flower primordium, by the action of some transcription factors, that are members of the MADS-box family. Among these, the functions of the B and C domain genes have been evolutionarily more conserved than the A domain gene. Many of these genes have arisen through gene duplications of ancestral members of this family.
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Early inductive effects of the axial mesoderm upon the overlying neural ectoderm is the mechanism that establishes the length dimension upon the brain primordium, jointly with establishing what is ventral in the brain (close to the axial mesoderm) in contrast with what is dorsal (distant from the axial mesoderm). Apart from the lack of a causal argument for introducing the axis in the telencephalon, there is the obvious difficulty that there is a pair of telencephalic vesicles, so that a bifid axis is actually implied in these outdated versions.
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Gonads start developing as a common primordium (an organ in the earliest stage of development), in the form of gonadal ridges, and only later are differentiated to male or female sex organs. The presence of the SRY gene, located on the Y chromosome and encoding the testis determining factor, determines male sexual differentiation. In the absence of the SRY gene from the Y chromosome, the female sex (ovaries instead of testes) will develop. The development of the gonads is a part of the development of the urinary and reproductive organs.
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Christine Mary Snow (Pilkington) (1902–1978) was an Oxford botanist who contributed to the study of geotropism and phyllotaxis. She is known for her co-development, with her husband George Snow, of Snows' rule, that a new primordium appears in a plant as soon as and in the place where it has enough space to do so. Mary Pilkington was the daughter of wealthy glass manufacturer Alfred 'Cecil' Pilkington (1875–1966). She was born in Rainhill, Lancashire, on 1 Aug 1902, and became an exhibitioner of St Hugh's College, Oxford in 1922.
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Le Douarin's work on chimeric embryos became increasingly notable, and she was able to gain international funding for her research after being appointed as Director of the C.N.R.S. Institute of Embryology. Building on her past experimentation, she began to research the developmental mechanism of the neural crest of avian embryos. In a 1980 publication, Le Douarin detailed her process of inserting totipotent quail nerve cells into the neural primordium of a chick. Her Feulgen stain technique allowed for the creation of a fate map detailing the migration of the quail- derived neural crest cells.
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Cajal-Retzius cells are the first cells to cover the cortical sheet and hippocampal primordium, and regulate cortical lamination by Reelin. In order to make connections with GABAergic neurons in different regions of the hippocampus (stratum oriens, stratum radiatum, and inner molecular layer), pioneer entorhinal neurons make synaptic contacts with Cajal-Retzius cells. To test their role in guidance, scientists (Del Rio and colleagues) ablated Cajal-Retzius cells with 6-OHDA. As a result, entorhinal axons did not grow in the hippocampus and ruled Cajal-Retzuis cells as guidepost cells.
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In invertebrates, the proneural genes, particularly the members of the achaete-scute complex(AS-C) promote neurogenesis, while the neurogenic genes prevent neurogenesis and facilitate epidermal development. The formation of neuroblasts depends on the Achaete- scute complex genes – achaete (ac), scute (sc), lethal of scute (lsc) and ventral nervous system defective (‘’vnd’’). However, only ‘’vnd’’ can control this formation process because this gene activates the expression of the others. ac, sc, lsc factors are initially expressed within the primordium of the embryonic central nervous system (neuroectoderm) in proneural clusters, from which single neuroblasts later arise.
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Histological analysis of cross-sections of the ribs indicate that they grew in three different phases as an individual developed. As is the case in most land vertebrates, the first phase involves the growth of a rib primordium that ossifies into a rib bone. The second phase, which deviates from most other land vertebrates, is the development of a shelf of bone above the main shaft of the rib to form the T-shape. The third and final phase is the widening of the lower ridge into a teardrop-like shape, reinforcing the rib.
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A primordium, the nascent leaf, forms at the least crowded part of the shoot meristem. The golden angle between successive leaves is the blind result of this jostling. Since three golden arcs add up to slightly more than enough to wrap a circle, this guarantees that no two leaves ever follow the same radial line from center to edge. The generative spiral is a consequence of the same process that produces the clockwise and counter-clockwise spirals that emerge in densely packed plant structures, such as Protea flower disks or pinecone scales.
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Silentium is framed with the in-universe conceit of collected Forerunner testimony and investigations recovered by 26th century humanity. The files in question are said to have been extracted from two sources: the carapace of a deceased Catalog (designated Forerunner remains #879) and a damaged monitor. Both the "Bornstellar Relation", the fictional document that encompasses the narrative of Halo: Cryptum and ONI's recovery of 343 Guilty Spark which acts as the framing device for the plot of Halo: Primordium, are referenced. On Erde-Tyrene, Catalog observes the evacuation effort of the planet.
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Cryptum received mixed reviews; some critics liked the Forerunner culture and suspense that Bear created, but others disliked the characters, found the plot too slow, and concluded that the novel was suited only to existing fans of the Halo series. Cryptum appeared on multiple bestseller lists after promotion on Halo Waypoint, a website that serves as a hub for Halo-related information. Primordium reached number seventeen on the New York Times Bestseller List in Hardcover Fiction. Silentium reached number eight on the New York Times Bestseller List for Hardcover Fiction.
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Thus, the interaction between them regulates the A/P axis of cortical primordium and directs the development map of cortical area. FGF8 signaling from the apical ectodermal ridge (AER), which borders the distal end of the limb bud, is necessary for forming normal limbs. In the absence of FGF8, limb buds can be reduced in size, hypoplasia or aplasia of bones or digits within the three limb segments may occur, as well as delays in subsequent expressions of other genes (Shh or FGF4). FGF8 is responsible for cell proliferation and survival, as well.
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A system of signaling centers, positioned strategically at the midline and edges of the cortex, produce secreted signaling proteins that establish concentration gradients in the cortical primordium. This provides positional information for each stem cell, and regulates proliferation, neurogenesis, and areal identity. After the initial establishment of areal identity, axons from the developing thalamus arrive at their correct cortical areal destination through the process of axon guidance and begin to form synapses. Many activity-dependent processes are then thought to play important roles in the maturation of each area.
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Tbx4 is a transcription factor and member of the T-box family, which have been shown to play important role in fetal development. Tbx4 is expressed in a wide variety of tissues during organogenesis, including the hindlimb, proctodeum, mandibular mesenchyme, lung mesenchyme, atrium of the heart and the body wall. Tbx4 is specifically expressed in the visceral mesoderm of the lung primordium and governs multiple processes during respiratory tract development such as initial endodermal bud development, respiratory endoderm formation, and septation of the respiratory tract and esophagus. Along with Tbx4, Tbx5 is also expressed to help with development of limbs.
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The cytoneme-mediated model suggests that Dpp is directly transported to target cells via actin-based filopodia called cytonemes that extend from the apical surface of Dpp- responding cells to the Dpp-producing source cells. These cytonemes have been observed, but the dependence of the Dpp gradient on cytonemes has not been definitively proven in imaginal wing discs. However, Dpp is known to be required for and sufficient to extend and maintain cytonemes. Experiments analyzing the dynamics between Dpp and cytonemes have been conducted in the air sac primordium, where Dpp signaling was found to have a functional link with cytonemes.
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Once expressed, the Fgf8 induces other transcription factors to form cross-regulatory loops between cells, thus the border is established. Through development, the Fgf8 goes to regulate the growth and differentiation of progenitor cells in this region to produce ultimate structure of midbrain and hindbrain. Crossely’s experiment proves that the Fgf8 is sufficient to induce the repatterning of midbrain and hindbrain structure. In the development of forebrain, cortical patterning centers are the boundaries or poles of cortical primordium, where multiple BMP and WNT genes are expressed. Besides, at the anterior pole several FGF family including Fgf3, 8,17 and 18 overlap in expression.
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This is principally because the primordium of the cranium during the period of fetal brain development is not yet ossified (hardened into bone through calcification). The tissue covering the embryonic cerebral cortex is several thin layers of ectoderm (future skin) and mesenchyme (future muscle and connective tissue, including the future cranium). These thin layers grow easily along with cortical expansion but eventually the cranial mesenchyme differentiates into cartilage; ossification of the cranial plates does not occur until later in development. The human cranium continues to grow substantially along with the brain after birth until the cranial plates finally fuse after several years.
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Thus, through manipulation of ARF19, the level and activity of auxin transporters PIN3 and LAX3 is inhibited. Once inhibited, auxin levels will be low in areas where lateral root emergence normally occurs, resulting in a failure for the plant to have the emergence of the lateral root primordium through the root pericycle. With this complex manipulation of Auxin transport in the roots, lateral root emergence will be inhibited in the roots and the root will instead elongate downwards, promoting vertical plant growth in an attempt to avoid shade. Research of Arabidopsis has led to the discovery of how this auxin mediated root response works.
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This same stimulus will also cause the meristem to follow a developmental pattern that will lead to the growth of floral meristems as opposed to vegetative meristems. The main difference between these two types of meristem, apart from the obvious disparity between the objective organ, is the verticillate (or whorled) phyllotaxis, that is, the absence of stem elongation among the successive whorls or verticils of the primordium. These verticils follow an acropetal development, giving rise to sepals, petals, stamens and carpels. Another difference from vegetative axillary meristems is that the floral meristem is «determined», which means that, once differentiated, its cells will no longer divide.
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The main difference between these two types of meristem, apart from the obvious disparity between the objective organ, is the verticillate (or whorled) phyllotaxis, that is, the absence of stem elongation among the successive whorls or verticils of the primordium. These verticils follow an acropetal development, giving rise to sepals, petals, stamens and carpels. Another difference from vegetative axillary meristems is that the floral meristem is "determined", which means that, once differentiated, its cells will no longer divide. The identity of the organs present in the four floral verticils is a consequence of the interaction of at least three types of gene products, each with distinct functions.
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Chinese Journal of Oceanology and Limnology, 11(2), 122-129. The only exception to this is the oral ciliature of the parent cell which is inherited by the proter daughter cell. The parental cirri are resorbed by the cell during division and the cirri of both daughter cells are produced de novo from cirral anlagen and the oral ciliature of the opisthe daughter cell is generated de novo through the formation of an oral primordium at the posterior end of the cell. Both the macronucleus and micronucleus divide during the process resulting in two daughter cells that are genetically identical to the parent cell.
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Studies of A. thaliana have provided considerable insights with regards to the genetics of leaf morphogenesis, particularly in dicotyledon-type plants. Much of the understanding has come from analyzing mutants in leaf development, some of which were identified in the 1960s, but were not analysed with genetic and molecular techniques until the mid-1990s. A. thaliana leaves are well suited to studies of leaf development because they are relatively simple and stable. Using A. thaliana, the genetics behind leaf shape development have become more clear and have been broken down into three stages: The initiation of the leaf primordium, the establishment of dorsiventrality, and the development of a marginal meristem.
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The link between primordium and millennium is well illustrated in Mormonism" (p. 140). and Abel in his ministry oft-quoted the Apostle Peter: "Think it not strange, brethren, concerning the fiery trials"Fiery trials" and affliction touched the lives of missionaries and potential gospel proselytes alike in the history of early Mormonism. As an illustration of this, and to provide a glimpse of Abel's exercise of priesthood power, Jackson (2014) presents instances of Abel's performance of ancillary priesthood ordinances while in the mission field. One was on behalf of Eunice Kinney, whose mind and spiritual sensibilities had become clouded by a spirit of darkness — her mind and soul "wracked" with doubt, frustration, and anger.
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In Drosophila, PGC migration begins with passive movement along the dorsal side of the embryo, during gastrulation. This is followed by more passive movement, due to the invagination of the posterior midgut primordium, which leads to the PGCs in the centre of the embryo, surrounded by epithelial cells that have been folded back on themselves. There is then a split into two groups, left and right respectively, as they actively migrate laterally across the epithelium to exit the gut, facilitated by fibroblast growth factor (FGF) signalling and a repulsion-based mechanism using enzymes encoded by the Wunen gene. This is followed by active movement dorsally along the basal side of the embryo.
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The experiment performed resembled the one done in 1918, however instead of a homoplastic transplantation they used embryos from two species of newt that are closely related. One of the benefits of using the cristatus and taeniatus embryos was that the cristatus embryo cells lacked pigment so the fate of the transplant could be easily tracked when placed among the pigmented taeniatus cells. A piece from the upper blastopore lip was removed from the cristatus embryo and transplanted into a ventral region of presumptive epidermis in the taeniatus embryo, away from the developing host blastopore. Following this transplant, they observed the formation of a secondary embryonic primordium, consistent with their previous work.
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The Spemann-Mangold organizer was first described in 1924 by Hans Spemann and Hilde Mangold. Prior to its discovery, it had been hypothesized by multiple groups that there exists a portion of the developing embryo that serves as a “organization center”. In 1918 and 1921, Hans Spemann showed that transplanting presumptive epidermis into the area of presumptive neural tissue would change the fate of the transplanted cells to that of their new destination, and likewise when he transplanted presumptive neural tissue to where the presumptive epidermis was forming. Spemann also showed that by transplanting a piece from the upper blastopore lip into an area of presumptive epidermis, a secondary embryonic primordium formed, including a secondary neural tube, notochord and somites.
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It implies that the planes of the brain are not necessarily the same as those of the body. However, the situation is more complex, since comparative embryology shows that the length axis of the neural tube (the primordium of the brain) has three internal bending points, namely two ventral bendings at the cervical and cephalic flexures (cervical flexure roughly between the medulla oblongata and the spinal cord, and cephalic flexure between the diencephalon and the midbrain), and a dorsal (pontine or rhombic flexure) at the midst of the hindbrain, behind the cerebellum. The latter flexure mainly appears in mammals and sauropsids (reptiles and birds), whereas the other two, and principally the cephalic flexure, appear in all vertebrates (the sum of the cervical and cephalic ventral flexures is the cause of the 90 degree angle mentioned above in humans between body axis and brain axis). This more realistic concept of the longitudinal structure of vertebrate brains implies that any section plane, except the sagittal plane, will intersect variably different parts of the same brain as the section series proceeds across it (relativity of actual sections with regard to topological morphological status in the ideal unbent neural tube).
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