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from article Rotifera

Four of the 8 or 9 recognized types of rotifer mastax. (a) Forcipate mastax of the monogonont Albertia vermiculus has all parts of the mallei and incus. (b) Incudate mastax of the monogonont Asplanchna brightwellii has enlarged, pincerlike rami and…

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from article Rotifera

Life cycles of the three rotifer groups. (a) Gonochoristic reproduction in seisonids. (b) Parthenogenesis alternating with sexual reproduction in monogononts. (c) Obligate parthenogenesis in bdelloids. 2n represents diploidy, and n represents…

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from article Apatite

Apatite. (a) Specimen from Snarum, Norway. (b) Common crystal habits.

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from article Andalusite

Andalusite crystals in metamorphic rock. (Credit: RF Company/Alamy)

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from article Andalusite

Phase diagram for the polymorphs of aluminum silicate (Al2SiO5). 1 km = 0.6 mi; 1 kb = 102 MPa.

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from article Calcarea

A calcareous sponge belonging to the family Leucettidae (order Clathrinida). (Credit: Bernard Dupont)

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from article Calcarea

Grades of construction of the water-current system in Calcarea: (a) asconoid type; (b) syconoid type without cortex; (c) syconoid type with cortex; (d) intermediate or transitional stage between syconoid and leuconoid types; (e) leuconoid type.…

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from article Calcarea

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from article Anoxic zone

Water column profiles from Saanich Inlet, an intermittent anoxic fiord in British Columbia, Canada. (a) Oxygen and hydrogen sulfide profiles showing the interface at 130 m (430 ft). (b) Dissolved iron and manganese at the same location. Pump cast…

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from article Anoxic zone

Schematic representation of trends in pore water profiles. Depth and concentration are arbitrary units but represent concentrations measured or inferred (in the case of O2) in equatorial Atlantic pore waters. (After P. Froelich et al., Early…

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from article Marine sediment

Shoal water sediments as examples of sedimentation without supply of land-derived sediment. (a) The Bahamas. (b) The Gulf of Batabano, which is in southwestern Cuba. Both of these shoals border directly on the deep ocean.

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from article Marine sediment

Sediment distribution of the northwestern Gulf of Mexico as an example of the sediments of a shelf with abundant land-derived sediment. Shelf depositional sediments and slope deposits are silty clays; nondepositional area is covered with relict…

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from article Marine sediment

Sediments on shelves with little land-derived sediment supply. (a) Off western coast of Florida. (b) Off northwestern Yucatan Peninsula.

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from article Marine sediment

Distribution of deep-sea sediments. (a) Major types. (b) Kaolinite concentration. (c) Montmorillonite concentrations. The concentrations are in the <2-μm-size fraction on a carbonate-opaline-silica-free basis.

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from article Marine sediment

Dissolved (a) oxygen (O2) and (b) nitrate (NO3−) in the interstitial water of a pelagic marine sediment. 1 cm = 0.4 in.

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from article Marine sediment

Dissolved (a) nitrate (NO3−), (b) manganese (Mn), and (c) iron (Fe) in the interstitial water from a hemipelagic marine sediment. Symbols represent different cores. 1 cm = 0.4 in.

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from article Marine sediment

Dissolved sulfate (SO42−) and methane from extremely reducing sediments in Saanich Inlet. 1 cm = 0.4 in.

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from article Marine sediment

Solubility of aragonite and calcite [expressed in terms of carbonate (CO32−) ion concentration] in seawater at 2°C (36°F) as a function of water depths in the North Atlantic and the eastern Equatorial Pacific. The intersections of the solubility…

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from article Marine sediment

Global organic carbon cycles. DOC = dissolved organic carbon; POC = particulate organic carbon. °F = (°C × 1.8) + 32; 1 m = 3.3 ft.

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from article Marine sediment

Rippled seafloor of sand being transported along the bed of a thermohaline current. From a water depth of 8900 ft (2700 m) on the northwest side of the Rockall Plateau, North Atlantic.

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from article Marine sediment

Lead-210 (210Pb) distribution in a sediment core (527-3) obtained by the research submersible Alvin from the Famous site (36°48.5′N, 33°15.3′W) on the Mid-Atlantic Ridge. The fit of the excess 210Pb [that is, unsupported by radium-226 (226Ra)]…

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from article Marine sediment

Distribution of 14C ages with depth in Famous core 527-3. The top 3.5 in. (9 cm) yield a constant age of 2400 years before present (B.P.) because of bioturbation. The deeper points define a line yielding a sediment accumulation rate of 2.9 cm/103…

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from article Marine sediment

Summary of major changes in the climate system over the past 800,000 years from a set of 18 proxy indicators. Coherent variations are evident in all components. (After J. Imbrie et al., On the structure and origin of major glaciation cycles, 1.…

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from article Peritrichia

Peritrichida. (a) Vorticella, a stalked peritrich. (b) Trichodina, a mobile peritrich.

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from article Ecological succession

A plant succession involves a predictable set of vegetative changes through a series of successional stages. (U.S. Environmental Protection Agency)

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from article Ecological succession

A spruce tree growing among a stand of cottonwoods. Spruce trees may eventually become the dominant species in this ecosystem. (U.S. National Park Service/Kay White)

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from article Oceanography

Oceanographic buoy stationed in the Aleutian Islands area of North Pacific Ocean. (Credit: NOAA Office of Marine and Aircraft Operations)

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from article Vesuvianite

Vesuvianite. (a) Crystal, Christiansand, Norway (specimen from Department of Geology, Bryn Mawr College). (b) Crystal habits (after C. Klein and C.S. Hurlbut, Jr., Manual of Mineralogy, 21st ed., 1993)

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from article Indian Ocean

Physiographic features of the Indian Ocean.

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from article Indian Ocean

Winds over the Indian Ocean.

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from article Indian Ocean

Surface currents of the Indian Ocean.

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from article Indian Ocean

Sea-surface temperature (°C) of Indian Ocean.

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from article Indian Ocean

Sea-surface salinity of the Indian Ocean in parts per thousand by weight (‰ ).

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from article Indian Ocean

Indian Ocean from the Arabian Sea to Antarctica showing (a) temperature (°C), (b) salinity (‰), (c) oxygen content (ml/liter), and (d) water masses.

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from article Indian Ocean

Mid-ocean ridge system of the Indian Ocean. DSDP = Deep Sea Drilling Project.

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from article Indian Ocean

Geotectonic image of the Indian Ocean as reflected in the satellite-derived gravity field of the region. A few specific structural features are identified as follows: Spreading centers: A, Carlsberg Ridge; B, Southwest Indian Ridge; C, Southeast…

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from article Porphyroblast

Porphyroblasts. (a) Porphyroblastic mica schist. Large crystals (porphyroblasts) of biotite mica formed late and replaced the rock except for the enclosed grains (quartz) aligned parallel to foliation. Smaller porphyroblasts of garnet replaced the…

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from article Priapulida

Priapulida. (a) Priapulus adult and (b) larva.

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from article Rock varnish

Varnished river cobble in western China.

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from article Rock varnish

Microlaminations seen in a varnish ultrathin section under a light microscope. Maximum varnish thickness is 150 μm.

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from article Insect physiology

Brood X cicada drying out after shedding its exoskeleton. (Credit: Michael J. Shirey)

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from article Insect physiology

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from article Insect physiology

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from article Hydrology

Diagram of the hydrologic cycle.

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from article Hydrology

Water flow scheme of the hydrologic cycle.

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from article Spearmint

Native spearmint (Mentha spicata). (Credit: Gerald D. Carr)

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from article Severe acute respiratory syndrome (SARS)

Electron microscopic image of a thin section of a severe acute respiratory syndrome coronavirus (SARS-CoV) within the cytoplasm of an infected cell, showing the spherical particles and cross sections through the viral nucleocapsid. (Credit: C. S.…

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from article Blueberry

Blueberries (Vaccinium sp.). (Photograph courtesy of Scott Bauer, Agricultural Research Service, United States Department of Agriculture)

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from article Blueberry

Mummy berry disease caused by the fungus Monilinia vaccinii-corymbosi. (a) Healthy fruit and (b) diseased fruit (from R. D. Milholland, Sclerotium germination and histopathology of Monilinia vaccinii-corymbosi on highbush blueberry, Phytopathology,…

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from article Botulism

A colony of Clostridium botulinum, the causative agent of botulism, growing on egg yolk agar. (Credit: Larry Stauffer/Centers for Disease Control and Prevention)

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from article Stenurida

Stenurida. (a) Ventral view of an arm and mouth frame plates of Bdellacoma vermiformis, a stenurid with long, slender arms. (b) Stenaster obtusus, a stenurid with short, broad arms. (After W. K. Spencer and C. W. Wright, Asterozoans, in R. C. Moore,…

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from article Cambrian

Cambrian, the first period of the Paleozoic Era.

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from article Cambrian

Reconstruction of the Lower Cambrian world. (After W. S. McKerrow, C. R. Scotese, and M. D. Brasier, Early Cambrian continental reconstructions. J. Geol. Soc., 149:599–606, 1992)

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from article Cambrian

North American divisions of the Cambrian System. Asterisks denote levels of major trilobite extinctions.

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from article Cambrian

Representative Cambrian fossils: (a–c) trilobites; (d–f) brachiopods; (g) hyolithid; (h–i) mollusks; (j–l) echinoderms; and (m, n) archaeocyathids.

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from article Sarcopterygii

Marbled or speckle-bellied lungfish (Protopterus aethiopicus). This African lungfish, a member of the class Sarcopterygii, can reach up to 2 m (6.6 ft) in length. (Photo by Joel Abroad)

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from article Onion

Pungent red onions (Allium cepa). (Photo by Stephen Ausmus, Agricultural Research Service, U.S. Department of Agriculture)

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from article Onion

Collection of yellow onions (Allium cepa) after harvesting. (Photo by Doug Wilson, Agricultural Research Service, U.S. Department of Agriculture)

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from article Onion

Common onions (Allium cepa) infected by Urocystis cepulae, causing onion smut. (Photo by Howard F. Schwartz, Colorado State University)

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from article Cryptomonadida

Examples of cryptomonads. (a) Chilomonas paramecium. (b) Cryptomonas erosa.

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from article Foot-and-mouth disease

Mouth of a steer with foot-and-mouth disease lesions on the tongue, along the lower gum, and inside the lower lip.

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from article Foot-and-mouth disease

Schematic diagram of the capsid of a foot-and- mouth disease virion. The four structural proteins, VP1–4 (also called 1A, 1B, 1C, and 1D), make up a protein subunit or protomer. Five protomers join to form a pentamer, and a capsid is an assembly of…

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from article Tarragon

Tarragon (Artemisia dracunculus). (Photo by Leo Michels)

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from article Particle track etching

Upper images show increasing radiation damage produced by a high-energy uranium nucleus in the cosmic radiation as it penetrates a thick stack of Lexan plastic sheets and slows down. The lengths of the etched cones in these three sheets, taken at…

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from article Particle track etching

Etched conical pits in a sheet of allyl diglycol carbonate (CR-39 plastic) irradiated at normal incidence with 60-MeV alpha particles. (From P. B. Price et al., Do energetic heavy nuclei penetrate deeply into the Earth's atmosphere?, Proc. Nat.…

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from article Particle track etching

Etched fossil particle tracks. (a) Tracks from spontaneous fission of 238U and 244Pu in a zircon crystal from a lunar breccia, seen by scanning electron microscopy (from D. Braddy et al., Crystal chemistry of Pu and U and concordant fission track…

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from article Particle track etching

Reconstructed images of right and left breasts of a patient taken by using a 3600-MeV carbon-ion beam at the Lawrence Berkeley Laboratory Bevalac accelerator. Arrow indicates 1-cm (0.4-in.) carcinoma. (From C. A. Tobias et al., Lawrence Berkeley…

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from article Medical ultrasonic tomography

Ultrasonic B-scan of the abdomen.

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from article Porcupine

North American porcupine (Erethizon dorsatum). (Photo from National Park Service)

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from article Borrelia

A digitally colorized scanning electron micrograph of a grouping of numerous Borrelia burgdorferi bacteria. The B. burgdorferi pathogen is responsible for causing Lyme disease, which is transmitted to humans by way of a tick bite. Borrelia…

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from article Magnetic observatory

Panoramic view of the San Juan, Puerto Rico geomagnetic observatory (foreground buildings) that is operated by the U.S. Geological Survey.

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from article Magnetic observatory

A typical magnetic sensor suite at an INTERMAGNET-standard observatory: (front) fluxgate variometer, (left) proton-precession magnetometer, (right) theodolite with small fluxgate attached to telescope.

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from article Magnetic observatory

Map showing the locations observatories that have been part of the INTERMAGNET consortium 1991–2011.

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from article Redwood

Redwood trees (Sequoia sempervirens). (Photo courtesy of Forest and Kim Starr)

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from article Coir

Coir fibers. (Photo courtesy of the Fiber Industry Development Authority, Department of Agriculture, the Philippines)

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from article Grassland ecosystem

Grasslands cover the Great Plains region in North America, extending from southern Texas into Canada. (Credit: U.S. Forest Service)

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from article Grassland ecosystem

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from article Xiphosurida

Segmentation of Limulus polyphemus. Inconclusive evidence indicates that there are 15 segments (6 in the prosoma, 9 in the opisthosoma). The telson (XV) may be a terminal spine that has become articulated and has incorporated the anus into its base.…

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from article Xiphosurida

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from article Xiphosurida

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from article Xiphosurida

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from article Xiphosurida

Embryonic and larval development of Limulus polyphemus. (a) Early embryo, side view. (b) Late embryo. (c) Yolk-filled digestive tract of larva. Note the segmentation of yolk in the newly hatched stage and the six lobes of digestive gland. (d) First…

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from article Xiphosurida

Morphology of adult male Limulus polyphemus. (a) Dorsal view. (b) Ventral view, appendages not shown. (c) Cross section through prosoma showing internal anatomy. (d) Posterior view. (e) Lateral view. (Copyright © McGraw Hill)

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from article Graywacke

Graywacke. (Credit: Doug Sherman/Geofile)

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from article Philosophy of science

Pulpit Rock Park in Colorado Springs, Colorado, photographed with camera equipment sensitive to infrared wavelengths of light outside of the visible portion of the electromagnetic spectrum that humans can perceive. The "invisible" light is rendered…

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from article Philosophy of science

Bust of the Greek polymath Aristotle. (Credit: Photos.com/Getty Images)

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from article Feather

Typical flight feather. (a) Full view. (b) Detail of base. (c) Detail of vane. (After J. Van Tyne and A. J. Berger, Fundamentals of Ornithology, 2d ed., John Wiley and Sons, 1976)

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from article Feather

Parts of three barbs from a vaned feather, showing the hooking mechanism of the overlapping barbules. (After J. C. Welty, The Life of Birds, Saunders, 1962)

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from article Feather

Types of feathers, (a) Filoplume. (b) Vane or contour. (c) Down. (d) Semiplume. (After J. C. Welty, The Life of Birds, Saunders, 1962)

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from article Feather

Section through growing feather follicle. (After R. I. C. Spearman, The keratinization of epidermal scales, feathers, and hairs, Biol. Rev., 41:59–69, 1966)

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from article Agricultural engineering

Drone used to inspect a vineyard in France. (Credit: freeprod/123RF)

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from article Water conservation

Drying lake because of drought. (Credit: Tim McCabe/USDA Natural Resources Conservation Service)

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from article Paleomagnetism

Field of an axial geocentric dipole. (After M. W. McElhinny, Palaeomagnetism and Plate Tectonics, Cambridge University Press, 1973)

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from article Paleomagnetism

Measuring head of the SQUID magnetometer (two-axis system).

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from article Paleomagnetism

Apparent polar wander path for North America for Late Carboniferous to recent time. The numbers represent time in millions of years before present. Circles represent one standard error about the mean. (After E. Irving, Paleopoles and paleolatitudes…

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from article Tay-Sachs disease

Healthy neuron (top) and neuron affected by Tay-Sachs disease (bottom). Defective hexosaminidase A enzyme activities in the case of Tay-Sachs disease allow lipid substrates to be stored in lysosomal compartments. This abnormal storage becomes toxic,…

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from article Tay-Sachs disease

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from article Tay-Sachs disease

Tay-Sachs disease results from mutations of a gene known as the HEX A gene, which encodes the α-subunit of the hexosaminidase A enzyme. When both partners are mutation carriers, each pregnancy has a 25% chance of being affected. (Copyright ©…

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from article Mylonite

Photomicrograph of greenschist-grade mylonite and ultramylonite derived from granodiorite, Borrego Springs shear zone, southern California. Half-arrows indicate right-lateral shear sense. Feldspar porphyroclasts (f), some with recrystallized tails…

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from article Pseudomonas

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