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2431) Edward Tatum

Gist:

Work

Organisms' metabolism–the chemical processes within its cells–are regulated by substances called enzymes. Edward Tatum and George Beadle proved in 1941 that our genetic code‚ our genes, govern the formation of enzymes. They exposed a type of mold to x-rays, causing mutations, or changes in its genes. They later succeeded in proving that this led to definite changes in enzyme formation. The conclusion was that each enzyme corresponds to a particular gene.

Summary

Edward L. Tatum (born Dec. 14, 1909, Boulder, Colo., U.S.—died Nov. 5, 1975, New York, N.Y.) was an American biochemist who helped demonstrate that genes determine the structure of particular enzymes or otherwise act by regulating specific chemical processes in living things. His research helped create the field of molecular genetics and earned him (with George Beadle and Joshua Lederberg) the Nobel Prize for Physiology or Medicine in 1958.

Tatum earned his doctorate from the University of Wisconsin in 1934. As a research associate at Stanford University (1937–41), Tatum collaborated with Beadle in an attempt to confirm the following concepts: all biochemical processes in all organisms are ultimately controlled by genes; all these processes are resolvable into series of individual sequential chemical reactions (pathways); each reaction is in some way controlled by a single gene; and the mutation of a single gene results only in an alteration in the ability of the cell to carry out a single chemical reaction.

At Stanford, Tatum and Beadle used X rays to induce mutations in strains of the pink bread mold Neurospora crassa. They found that some of the mutants lost the ability to produce an essential amino acid or vitamin. Tatum and Beadle then crossed these strains with normal strains of the mold and found that their offspring inherited the metabolic defect as a recessive trait, thereby proving that the mutations were in fact genetic defects. Their research showed that when a genetic mutation can be shown to affect a specific chemical reaction, the enzyme catalyzing that reaction will be altered or missing. Thus, they showed that each gene in some way determines the structure of a specific enzyme (the one-gene–one-enzyme hypothesis).

As a professor at Yale University (1945–48), Tatum successfully applied his methods of inducing mutations and studying biochemical processes in Neurospora to bacteria. With Lederberg, he discovered the occurrence of genetic recombination, or “sex,” between Escherichia coli bacteria of the K-12 strain. Largely because of their efforts, bacteria became the primary source of information concerning the genetic control of biochemical processes in the cell.

Tatum returned to Stanford in 1948 and joined the staff of the Rockefeller Institute for Medical Research (now Rockefeller University), New York City, in 1957.

Details

Edward Lawrie Tatum (December 14, 1909 – November 5, 1975) was an American geneticist. He shared half of the Nobel Prize in Physiology or Medicine in 1958 with George Beadle for showing that genes control individual steps in metabolism. The other half of that year's award went to Joshua Lederberg. Tatum was an elected member of the United States National Academy of Sciences, the American Philosophical Society, and the American Academy of Arts and Sciences.

Education

Edward Lawrie Tatum was born on December 14, 1909, in Boulder, Colorado to Arthur L. Tatum and Mabel Webb Tatum. Arthur L. Tatum was a chemistry professor, who by 1925 was a professor of pharmacology at the University of Wisconsin at Madison.

Edward Lawrie Tatum attended college at the University of Chicago for two years, before transferring to the University of Wisconsin–Madison, where he received his BA in 1931 and PhD in 1934. His dissertation was Studies in the biochemistry of microorganisms (1934).

Career

Starting in 1937, Tatum worked at Stanford University, where he began his collaboration with Beadle. He then moved to Yale University in 1945 where he mentored Lederberg. He returned to Stanford in 1948 and then joined the faculty of Rockefeller Institute in 1957. He remained there until his death on November 5, 1975, in New York City. A heavy cigarette smoker, Tatum died of heart failure complicated by chronic emphysema. His last wife Elsie Bergland died in 1998.

Research

Tatum and Beadle carried out pioneering studies of biochemical mutations in Neurospora, published in 1941. Their work provided a prototype of the investigation of gene action and a new and effective experimental methodology for the analysis of mutations in biochemical pathways. Beadle and Tatum's key experiments involved exposing the bread mold Neurospora crassa to x-rays, causing mutations. In a series of experiments, they showed that these mutations caused changes in specific enzymes involved in metabolic pathways. This led them to propose a direct link between genes and enzymatic reactions, known as the "one gene, one enzyme" hypothesis.

Tatum spent his career studying biosynthetic pathways and the genetics of bacteria. An active area of research in his laboratory was to understand the basis of Tryptophan biosynthesis in Escherichia coli. Tatum and his student Joshua Lederberg showed that E. coli could share genetic information through recombination.

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2705.

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#10743. What does the term in Biology G protein mean?

#10744. What does the term in Biology Gamete mean?

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#2566. What does the medical term Normocytic anemia mean?

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#9851.

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2704.

2492) Himalayan Mountains

Gist

The Himalayas are a massive mountain range in Asia, forming a crescent-shaped arc that separates the Indian subcontinent from the Tibetan Plateau and stretches across five countries: India, Nepal, Bhutan, China (Tibet), and Pakistan. Known as the "abode of snow," they contain Earth's highest peaks, including Mount Everest, and influence the climate and rivers of South Asia. 

The Himalayas consists of four parallel mountain ranges from south to north: the Sivalik Hills on the south; the Lower Himalayan Range; the Great Himalayas, which is the highest and central range; and the Tibetan Himalayas on the north. The Karakoram are generally considered separate from the Himalayas.

Summary

The Himalayas, or Himalaya, is a mountain range in Asia separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the Earth's highest peaks, including the highest, Mount Everest. More than 100 peaks exceeding elevations of 7,200 m (23,600 ft) above sea level lie in the Himalayas.

The Himalayas abut on or cross territories of five countries: Nepal, India, China, Bhutan and Pakistan. The sovereignty of the range in the Kashmir region is disputed among India, Pakistan, and China. The Himalayan range is bordered on the northwest by the Karakoram and Hindu Kush ranges, on the north by the Tibetan Plateau, and on the south by the Indo-Gangetic Plain. Some of the world's major rivers, the Indus, the Ganges, and the Tsangpo–Brahmaputra, rise in the vicinity of the Himalayas, and their combined drainage basin is home to some 600 million people; 53 million people live in the Himalayas. The Himalayas have profoundly shaped the cultures of South Asia and Tibet. Many Himalayan peaks are sacred in Hinduism and Buddhism. The summits of several—Kangchenjunga (from the Indian side), Gangkhar Puensum, Machapuchare, Nanda Devi, and Kailash in the Tibetan Transhimalaya—are off-limits to climbers.

The Himalayas were uplifted after the collision of the Indian tectonic plate with the Eurasian plate, specifically, by the folding, or nappe-formation of the uppermost Indian crust, even as a lower layer continued to push on into Tibet and add thickness to its plateau; the still lower crust, along with the mantle, however, subducted under Eurasia. The Himalayan mountain range runs west-northwest to east-southeast in an arc 2,400 km (1,500 mi) long. Its western anchor, Nanga Parbat, lies just south of the northernmost bend of the Indus river. Its eastern anchor, Namcha Barwa, lies immediately west of the great bend of the Yarlung Tsangpo River. The Indus-Yarlung suture zone, along which the headwaters of these two rivers flow, separates the Himalayas from the Tibetan plateau; the rivers also separate the Himalayas from the Karakorams, the Hindu Kush, and the Transhimalaya. The range varies in width from 350 km (220 mi) in the west to 151 km (94 mi) in the east.

Details

Himalayas are great mountain system of Asia forming a barrier between the Plateau of Tibet to the north and the alluvial plains of the Indian subcontinent to the south. The Himalayas include the highest mountains in the world, with more than 110 peaks rising to elevations of 24,000 feet (7,300 meters) or more above sea level. One of those peaks is Mount Everest (Tibetan: Chomolungma; Chinese: Qomolangma Feng; Nepali: Sagarmatha), the world’s highest, with an elevation of 29,032 feet (8,849 meters).

For thousands of years the Himalayas have held a profound significance for the peoples of South Asia, as their literature, mythologies, and religions reflect. Since ancient times the vast glaciated heights have attracted the attention of the pilgrim mountaineers of India, who coined the Sanskrit name Himalaya—from hima (“snow”) and alaya (“abode”)—for that great mountain system. In contemporary times the Himalayas have offered the greatest attraction and the greatest challenge to mountaineers throughout the world.

The ranges, which form the northern border of the Indian subcontinent and an almost impassable barrier between it and the lands to the north, are part of a vast mountain belt that stretches halfway around the world from North Africa to the Pacific Ocean coast of Southeast Asia. The Himalayas themselves stretch uninterruptedly for about 1,550 miles (2,500 km) from west to east between Nanga Parbat (26,660 feet [8,126 meters]), in the Pakistani-administered portion of the Kashmir region, and Namjagbarwa (Namcha Barwa) Peak (25,445 feet [7,756 meters]), in the Tibet Autonomous Region of China. Between those western and eastern extremities lie the two Himalayan countries of Nepal and Bhutan. The Himalayas are bordered to the northwest by the mountain ranges of the Hindu Kush and the Karakoram and to the north by the high and vast Plateau of Tibet. The width of the Himalayas from south to north varies between 125 and 250 miles (200 and 400 km). Their total area amounts to about 230,000 square miles (595,000 square km).

Though India, Nepal, and Bhutan have sovereignty over most of the Himalayas, Pakistan and China also occupy parts of them. In the disputed Kashmir region, Pakistan has administrative control of some 32,400 square miles (83,900 square km) of the range lying north and west of the “line of control” established between India and Pakistan in 1972. China administers some 14,000 square miles (36,000 square km) in the Ladakh region and has claimed territory at the eastern end of the Himalayas within the Indian state of Arunachal Pradesh. Those disputes accentuate the boundary problems faced by India and its neighbors in the Himalayan region.

Physical features

The most characteristic features of the Himalayas are their soaring heights, steep-sided jagged peaks, valley and alpine glaciers often of stupendous size, topography deeply cut by erosion, seemingly unfathomable river gorges, complex geologic structure, and series of elevational belts (or zones) that display different ecological associations of flora, fauna, and climate. Viewed from the south, the Himalayas appear as a gigantic crescent with the main axis rising above the snow line, where snowfields, alpine glaciers, and avalanches all feed lower-valley glaciers that in turn constitute the sources of most of the Himalayan rivers. The greater part of the Himalayas, however, lies below the snow line. The mountain-building process that created the range is still active. As the bedrock is lifted, considerable stream erosion and gigantic landslides occur.

The Himalayan ranges can be grouped into four parallel longitudinal mountain belts of varying width, each having distinct physiographic features and its own geologic history. They are designated, from south to north, as the Outer, or Sub-, Himalayas (also called the Siwalik Range); the Lesser, or Lower, Himalayas; the Great Himalaya Range (Great Himalayas); and the Tethys, or Tibetan, Himalayas. Farther north lie the Trans-Himalayas in Tibet proper. From west to east the Himalayas are divided broadly into three mountainous regions: western, central, and eastern.

Geologic history

Over the past 65 million years, powerful global plate-tectonic forces have moved Earth’s crust to form the band of Eurasian mountain ranges—including the Himalayas—that stretch from the Alps to the mountains of Southeast Asia.

During the Jurassic Period (about 201 to 145 million years ago), a deep crustal downwarp—the Tethys Ocean—bordered the entire southern fringe of Eurasia, then excluding the Arabian Peninsula and the Indian subcontinent. About 180 million years ago, the old supercontinent of Gondwana (or Gondwanaland) began to break up. One of Gondwana’s fragments, the lithospheric plate that included the Indian subcontinent, pursued a northward collision course toward the Eurasian Plate during the ensuing 130 to 140 million years. The Indian-Australian Plate gradually confined the Tethys trench within a giant pincer between itself and the Eurasian Plate. As the Tethys trench narrowed, increasing compressive forces bent the layers of rock beneath it and created interlacing faults in its marine sediments. Masses of granites and basalts intruded from the depth of the mantle into that weakened sedimentary crust. Between about 40 and 50 million years ago, the Indian subcontinent finally collided with Eurasia. The plate containing India was sheared downward, or subducted, beneath the Tethys trench at an ever-increasing pitch.

During the next 30 million years, shallow parts of the Tethys Ocean gradually drained as its sea bottom was pushed up by the plunging Indian-Australian Plate; that action formed the Plateau of Tibet. On the plateau’s southern edge, marginal mountains—the Trans-Himalayan ranges of today—became the region’s first major watershed and rose high enough to become a climatic barrier. As heavier rains fell on the steepening southern slopes, the major southern rivers eroded northward toward the headwaters with increasing force along old transverse faults and captured the streams flowing onto the plateau, thus laying the foundation for the drainage patterns for a large portion of Asia. To the south the northern reaches of the Arabian Sea and the Bay of Bengal rapidly filled with debris carried down by the ancestral Indus, Ganges (Ganga), and Brahmaputra rivers. The extensive erosion and deposition continue even now as those rivers carry immense quantities of material every day.

Finally, some 20 million years ago, during the early Miocene Epoch, the tempo of the crunching union between the two plates increased sharply, and Himalayan mountain building began in earnest. As the Indian subcontinental plate continued to plunge beneath the former Tethys trench, the topmost layers of old Gondwana metamorphic rocks peeled back over themselves for a long horizontal distance to the south, forming nappes. Wave after wave of nappes thrust southward over the Indian landmass for as far as 60 miles (about 100 km). Each new nappe consisted of Gondwana rocks older than the last. In time those nappes became folded, contracting the former trench by some 250 to 500 horizontal miles (400 to 800 km). All the while, downcutting rivers matched the rate of uplift, carrying vast amounts of eroded material from the rising Himalayas to the plains where it was dumped by the Indus, Ganges, and Brahmaputra rivers. The weight of that sediment created depressions, which in turn could hold more sediment. In some places the alluvium beneath the Indo-Gangetic Plain now exceeds 25,000 feet (7,600 meters) in depth.

Probably only within the past 600,000 years, during the Pleistocene Epoch (roughly 2,600,000 to 11,700 years ago), did the Himalayas become the highest mountains on Earth. If strong horizontal thrusting characterized the Miocene and the succeeding Pliocene Epoch (about 23 to 2.6 million years ago), intense uplift epitomized the Pleistocene. Along the core zone of the northernmost nappes—and just beyond—crystalline rocks containing new gneiss and granite intrusions emerged to produce the staggering crests seen today. On a few peaks, such as Mount Everest, the crystalline rocks carried old fossil-bearing Tethys sediments from the north piggyback to the summits.

Once the Great Himalayas had risen high enough, they became a climatic barrier: the marginal mountains to the north were deprived of rain and became as parched as the Plateau of Tibet. In contrast, on the wet southern flanks the rivers surged with such erosive energy that they forced the crest line to migrate slowly northward.

Simultaneously, the great transverse rivers breaching the Himalayas continued their downcutting in pace with the uplift. Changes in the landscape, however, compelled all but those major rivers to reroute their lower courses because, as the northern crests rose, so also did the southern edge of the extensive nappes. The formations of the Siwalik Series were overthrust and folded, and in between the Lesser Himalayas downwarped to shape the midlands. Now barred from flowing due south, most minor rivers ran east or west through structural weaknesses in the midlands until they could break through the new southern barrier or join a major torrent.

In some valleys, such as the Vale of Kashmir and the Kathmandu Valley of Nepal, lakes formed temporarily and then filled with Pleistocene deposits. After drying up some 200,000 years ago, the Kathmandu Valley rose at least 650 feet (200 meters), an indication of localized uplift within the Lesser Himalayas.

Physiography of the Himalayas

The Outer Himalayas comprise flat-floored structural valleys and the Siwalik Range, which borders the Himalayan mountain system to the south. Except for small gaps in the east, the Siwaliks run for the entire length of the Himalayas, with a maximum width of 62 miles (100 km) in the northern Indian state of Himachal Pradesh. In general, the 900-foot (275-meter) elevation contour line marks their southern boundary; they rise an additional 2,500 feet (760 meters) to the north. The main Siwalik Range has steeper southern slopes facing the Indian plains and descends gently northward to flat-floored basins, called duns. The best-known of those is the Dehra Dun, in southern Uttarakhand state, just north of the border with northwestern Uttar Pradesh state.

To the north the Siwalik Range abuts a massive mountainous tract, the Lesser Himalayas. In that range, 50 miles (80 km) in width, mountains rising to 15,000 feet (4,500 meters) and valleys with elevations of 3,000 feet (900 meters) run in varying directions. Neighboring summits share similar elevations, creating the appearance of a highly dissected plateau. The three principal ranges of the Lesser Himalayas—the Nag Tibba, the Dhaola Dhar, and the Pir Panjal—have branched off from the Great Himalaya Range lying farther north. The Nag Tibba, the most easterly of the three ranges, reaches an elevation of some 26,800 feet (8,200 meters) near its eastern end, in Nepal, and forms the watershed between the Ganges and Yamuna rivers in Uttarakhand.

To the west is the picturesque Vale of Kashmir, in Jammu and Kashmir union territory (the Indian-administered portion of Kashmir). A structural basin (i.e., an elliptical basin in which the rock strata are inclined toward a central point), the vale forms an important section of the Lesser Himalayas. It extends from southeast to northwest for 100 miles (160 km), with a width of 50 miles (80 km), and has an average elevation of 5,100 feet (1,600 meters). The basin is traversed by the meandering Jhelum River, which runs through Wular Lake, a large freshwater lake in Jammu and Kashmir northwest of Srinagar.

The backbone of the entire mountain system is the Great Himalaya Range, rising into the zone of perpetual snow. The range reaches its maximum height in Nepal; among its peaks are 10 of the 13 highest in the world, each of which exceeds 26,250 feet (8,000 meters) in elevation. From west to east those peaks are Nanga Parbat, Dhaulagiri 1, Annapurna 1, Manaslu 1, Xixabangma (Gosainthan), Cho Oyu, Mount Everest, Lhotse, Makalu 1, and Kanchenjunga 1.

The range trends northwest-southeast from Jammu and Kashmir to Sikkim, an old Himalayan kingdom that is now a state of India. East of Sikkim it runs east-west for another 260 miles (420 km) through Bhutan and the eastern part of Arunachal Pradesh as far as the peak of Kangto (23,260 feet [7090 meters]) and finally bends northeast, terminating at Namcha Barwa.

There is no sharp boundary between the Great Himalayas and the ranges, plateaus, and basins lying to the north of the Great Himalayas. Those are generally grouped together under the names of the Tethys, or Tibetan, Himalayas and the Trans-Himalayas, which extend far northward into Tibet. In Kashmir and in the Indian state of Himachal Pradesh, the Tethys are at their widest, forming the Spiti Basin and the Zanskar Range.

Drainage of the Himalayas

The Himalayas are drained by 19 major rivers, of which the Indus and the Brahmaputra are the largest, each having catchment basins in the mountains of about 100,000 square miles (260,000 square km) in extent. Five of the 19 rivers, with a total catchment area of about 51,000 square miles (132,000 square km), belong to the Indus system—the Jhelum, the Chenab, the Ravi, the Beas, and the Sutlej—and collectively define the vast region divided between Punjab state in India and Punjab province in Pakistan. Of the remaining rivers, nine belong to the Ganges system—the Ganges, Yamuna, Ramganga, Kali (Kali Gandak), Karnali, Rapti, Gandak, Baghmati, and Kosi rivers—draining roughly 84,000 square miles (218,000 square km) in the mountains, and three belong to the Brahmaputra system—the Tista, the Raidak, and the Manas—draining another 71,000 square miles (184,000 square km) in the Himalayas.

The major Himalayan rivers rise north of the mountain ranges and flow through deep gorges that generally reflect some geologic structural control, such as a fault line. The rivers of the Indus system as a rule follow northwesterly courses, whereas those of the Ganges-Brahmaputra systems generally take easterly courses while flowing through the mountain region.

To the north of India, the Karakoram Range, with the Hindu Kush range on the west and the Ladakh Range on the east, forms the great water divide, shutting off the Indus system from the rivers of Central Asia. The counterpart of that divide on the east is formed by the Kailas Range and its eastward continuation, the Nyainqêntanglha (Nyenchen Tangla) Mountains, which prevent the Brahmaputra from draining the area to the north. South of that divide, the Brahmaputra flows to the east for about 900 miles (1,450 km) before cutting across the Great Himalaya Range in a deep transverse gorge, although many of its Tibetan tributaries flow in an opposite direction, as the Brahmaputra may once have done.

The Great Himalayas, which normally would form the main water divide throughout their entire length, function as such only in limited areas. That situation exists because the major Himalayan rivers, such as the Indus, the Brahmaputra, the Sutlej, and at least two headwaters of the Ganges—the Alaknanda and the Bhagirathi—are probably older than the mountains they traverse. It is believed that the Himalayas were uplifted so slowly that the old rivers had no difficulty in continuing to flow through their channels and, with the rise of the Himalayas, acquired an even greater momentum, which enabled them to cut their valleys more rapidly. The elevation of the Himalayas and the deepening of the valleys thus proceeded simultaneously. As a result, the mountain ranges emerged with a completely developed river system cut into deep transverse gorges that range in depth from 5,000 to 16,000 feet (1,500 to 5,000 meters) and in width from 6 to 30 miles (10 to 50 km). The earlier origin of the drainage system explains the peculiarity that the major rivers drain not only the southern slopes of the Great Himalayas but, to a large extent, its northern slopes as well, the water divide being north of the crest line.

The role of the Great Himalaya Range as a watershed, nevertheless, can be seen between the Sutlej and Indus valleys for 360 miles (580 km); the drainage of the northern slopes is carried by the north-flowing Zanskar and Dras rivers, which drain into the Indus. Glaciers also play an important role in draining the higher elevations and in feeding the Himalayan rivers. Several glaciers occur in Uttarakhand, of which the largest, the Gangotri, is 20 miles (32 km) long and is one of the sources of the Ganges. The Khumbu Glacier drains the Everest region in Nepal and is one of the most popular routes for the ascent of the mountain. The rate of movement of the Himalayan glaciers varies considerably; in the neighboring Karakoram Range, for example, the Baltoro Glacier moves about 6 feet (2 meters) per day, while others, such as the Khumbu, move only about 1 foot (30 cm) daily. Most of the Himalayan glaciers are in retreat, at least in part because of climate change.

Soils

The north-facing slopes generally have a fairly thick soil cover, supporting dense forests at lower elevations and grasses higher up. The forest soils are dark brown in color and silt loam in texture; they are ideally suited for growing fruit trees. The mountain meadow soils are well developed but vary in thickness and in their chemical properties. Some of the wet deep upland soils of that type in the eastern Himalayas—for example, in the Darjeeling (Darjiling) Hills and in the Assam valley—have a high humus content that is good for growing tea. Podzolic soils (infertile acidic forest soils) occur in a belt some 400 miles (640 km) long in the valleys of the Indus and its tributary the Shyok River, to the north of the Great Himalaya Range, and in patches in Himachal Pradesh. Farther east, saline soils occur in the dry high plains of the Ladakh region. Of the soils that are not restricted to any particular area, alluvial soils (deposited by running water) are the most productive, though they occur in limited areas, such as the Vale of Kashmir, the Dehra Dun, and the high terraces flanking the Himalayan valleys. Lithosols, consisting of imperfectly weathered rock fragments that are deficient in humus content, cover many large areas at high elevations and are the least-productive soils.

Climate of the Himalayas

The Himalayas, as a great climatic divide affecting large systems of air and water circulation, help determine meteorological conditions in the Indian subcontinent to the south and in the Central Asian highlands to the north. By virtue of its location and stupendous height, the Great Himalaya Range obstructs the passage of cold continental air from the north into India in winter and also forces the southwesterly monsoon (rain-bearing) winds to give up most of their moisture before crossing the range northward. The result is heavy precipitation (both rain and snow) on the Indian side but arid conditions in Tibet. The average annual rainfall on the south slopes varies between 60 inches (1,530 mm) at Shimla, Himachal Pradesh, and Mussoorie, Uttarakhand, in the western Himalayas and 120 inches (3,050 mm) at Darjeeling, West Bengal state, in the eastern Himalayas. North of the Great Himalayas, at places such as Skardu, Gilgit, and Leh in the Ladakh portion of the Indus valley, only 3 to 6 inches (75 to 150 mm) of precipitation occur.

Local relief and location determine climatic variation not only in different parts of the Himalayas but even on different slopes of the same range. Because of its favorable location on top of the Mussoorie Range facing the Dehra Dun, the town of Mussoorie, for example, at an elevation of about 6,100 feet (1,900 meters), receives 92 inches (2,335 mm) of precipitation annually, compared with 62 inches (1,575 mm) in the town of Shimla, which lies some 90 miles (145 km) to the northwest behind a series of ridges reaching 6,600 feet (2,000 meters). The eastern Himalayas, which are at a lower latitude than the western Himalayas, are relatively warmer. The average minimum temperature for the month of May, recorded in Darjeeling at an elevation of 6,380 feet (1,945 meters), is 52 °F (11 °C). In the same month, at an elevation of 16,500 feet (5,000 meters) in the neighborhood of Mount Everest, the minimum temperature is about 17 °F (−8 °C); at 19,500 feet (6,000 meters) it falls to −8 °F (−22 °C), the lowest minimum having been −21 °F (−29 °C); during the day, in areas sheltered from strong winds that often blow at more than 100 miles (160 km) per hour, the sun is often pleasantly warm, even at high elevations.

There are two periods of precipitation: the moderate amounts brought by winter storms and the heavier precipitation of summer, with its southwesterly monsoon winds. During winter, low-pressure weather systems advance into the Himalayas from the west and cause heavy snowfall. Within the regions where western disturbances are felt, condensation occurs in upper air levels, and, as a result, precipitation is much greater over the high mountains. During that season snow accumulates around the Himalayan high peaks, and precipitation is greater in the west than the east. In January, for example, Mussoorie in the west receives almost 3 inches (75 mm), whereas Darjeeling to the east receives less than 1 inch (25 mm). By the end of May the meteorological conditions have reversed. Southwesterly monsoon currents channel moist air toward the eastern Himalayas, where the moisture rising over the steep terrain cools and condenses to fall as rain or snow; in June, therefore, Darjeeling receives about 24 inches (600 mm) and Mussoorie less than 8 inches (200 mm). The rain and snow cease in September, after which the finest weather in the Himalayas prevails until the beginning of winter in December.

Plant life

Himalayan vegetation can be broadly classified into four types—tropical, subtropical, temperate, and alpine—each of which prevails in a zone determined mainly by elevation and precipitation. Local differences in relief and climate, as well as exposure to sunlight and wind, cause considerable variation in the species present within each zone. Tropical evergreen rainforest is confined to the humid foothills of the eastern and central Himalayas. The evergreen dipterocarps—a group of timber- and resin-producing trees—are common; their different species grow on different soils and on hill slopes of varying steepness. Ceylon ironwood (Mesua ferrea) is found on porous soils at elevations between 600 and 2,400 feet (180 and 720 meters); bamboos grow on steep slopes; oaks (genus Quercus) and Indian horse chestnuts (Aesculus indica) grow on the lithosol (shallow soils consisting of imperfectly weathered rock fragments), covering sandstones from Arunachal Pradesh westward to central Nepal at elevations from 3,600 to 5,700 feet (1,100 to 1,700 meters). Alder trees (genus Alnus) are found along the watercourses on the steeper slopes. At higher elevations those species give way to mountain forests in which the typical evergreen is the Himalayan screw pine (Pandanus furcatus). Besides those trees, some 4,000 species of flowering plants, of which 20 are palms, are estimated to occur in the eastern Himalayas.

With decreasing precipitation and increasing elevation westward, the rainforests give way to tropical deciduous forests, where the valuable timber tree sal (Shorea robusta) is the dominant species. Wet sal forests thrive on high plateaus at elevations of about 3,000 feet (900 meters), while dry sal forests prevail higher up, at 4,500 feet (1,400 meters). Farther west, steppe forest (i.e., expanse of grassland dotted with trees), steppe, subtropical thorn steppe, and subtropical semidesert vegetation occur successively. Temperate mixed forests extend from about 4,500 to roughly 11,000 feet (1,400 to 3,400 meters) and contain conifers and broad-leaved temperate trees. Evergreen forests of oaks and conifers have their westernmost outpost on the hills above Murree, some 30 miles (50 km) northwest of Rawalpindi, in Pakistan; those forests are typical of the Lesser Himalayas, being conspicuous on the outer slopes of the Pir Panjal, in Jammu and Kashmir union territory. Chir pine (Pinus roxburghii) is the dominant species at elevations from 2,700 to 5,400 feet (800 to 1,600 meters). In the inner valleys that species may occur even up to 6,300 feet (1,900 meters). Deodar cedar (Cedrus deodara), a highly valued endemic species, grows mainly in the western part of the range. Stands of that species occur between 6,300 and 9,000 feet (1,900 and 2,700 meters) and tend to grow at still higher elevations in the upper valleys of the Sutlej and Ganges rivers. Of the other conifers, blue pine (Pinus wallichiana) and morinda spruce (Picea smithiana) first appear between about 7,300 and 10,000 feet (2,200 and 3,000 meters).

The alpine zone begins above the tree line, between elevations of 10,500 and 11,700 feet (3,200 and 3,600 meters), and extends up to about 13,700 feet (4,200 meters) in the western Himalayas and 14,600 feet (4,500 meters) in the eastern Himalayas. In that zone can be found all the wet and moist alpine vegetation. Juniper (genus Juniperus) is widespread, especially on sunny sites, steep and rocky slopes, and drier areas. Rhododendron occurs everywhere but is more abundant in the wetter parts of the eastern Himalayas, where it grows in all sizes from trees to low shrubs. Mosses and lichens grow in shaded areas at lower levels in the alpine zone where the humidity is high; flowering plants are found at high elevations.

Animal life

The fauna of the eastern Himalayas is similar to that of the southern Chinese and Southeast Asian region. Many of those species are primarily found in tropical forests and are only secondarily adapted to the subtropical, mountain, and temperate conditions prevailing at higher elevations and in the drier western areas. The animal life of the western Himalayas, however, has more affinities with that of the Mediterranean, Ethiopian, and Turkmenian regions. The past presence in the region of some African animals, such as giraffes and the hippopotamuses, can be inferred from fossil remains in deposits found in the Siwalik Range. The animal life at elevations above the tree line consists almost exclusively of cold-tolerant endemic species that evolved from the wildlife of the steppes after the uplift of the Himalayas. Elephants and rhinoceroses are restricted to parts of the forested Tarai region—moist or marshy areas, now largely drained—at the base of the low hills in southern Nepal. Asiatic black bears, clouded leopards, langurs (a long-tailed Asian monkey), and Himalayan goat antelopes (e.g., the tahr) are some of the denizens of the Himalayan forests. The Indian rhinoceros was once abundant throughout the foothill zone of the Himalayas but is now endangered, as is the musk deer; both species are dwindling, and few live, other than those in a handful of reserves set up to protect them. The Kashmir stag, or hangul, is near extinction.

In remote sections of the Himalayas, at higher elevations, snow leopards, brown bears, lesser pandas, and Tibetan yaks have limited populations. The yak has been domesticated and is used as a beast of burden in Ladakh. Above the tree line the most numerous animals, however, are diverse types of insects, spiders, and mites, which are the only animal forms that can live as high up as 20,700 feet (6,300 meters).

Fish of the genus Glyptothorax live in most of the Himalayan streams, and the Himalayan water shrew inhabits stream banks. Lizards of the genus Japalura are widely distributed. Typhlops, a genus of blind snake, is common in the eastern Himalayas. The butterflies of the Himalayas are extremely varied and beautiful, especially those in the genus Troides.

Bird life in the Himalayas is equally rich but is more abundant in the east than in the west. In Nepal alone almost 800 species have been observed. Among some of the common Himalayan birds are different species of magpies (including the black-rumped, the blue, and the racket-tailed), titmice, choughs (related to the jackdaw), whistling thrushes, and redstarts. A few strong fliers, such as the lammergeier (bearded vulture), the black-eared kite, and the Himalayan griffon (an Old World vulture), also can be seen. Snow partridges and Cornish choughs are found at elevations of 18,600 feet (5,700 meters).

Of the four principal language families in the Indian subcontinent—Indo-European, Tibeto-Burman, Austroasiatic, and Dravidian—the first two are well represented in the Himalayas. In ancient times, peoples speaking languages from both families mixed in varying proportions in different areas. Their distribution is the result of a long history of penetrations by Central Asian and Iranian groups from the west, Indian peoples from the south, and Asian peoples from the east and north. In Nepal, which constitutes the middle third of the Himalayas, those groups overlapped and intermingled. The penetrations of the lower Himalayas were instrumental to the migrations into and through the river-plain passageways of South Asia.

Generally speaking, the Great Himalayas and the Tethys Himalayas are inhabited by Tibetans and peoples speaking other Tibeto-Burman languages, while the Lesser Himalayas are the home of Indo-European language speakers. Among the latter are the Kashmiri people of the Vale of Kashmir and the Gaddi and Gujari, who live in the hilly areas of the Lesser Himalayas. Traditionally, the Gaddi are a hill people; they possess large flocks of sheep and herds of goats and go down with them from their snowy abode in the Outer Himalayas only in winter, returning again to the highest pastures in June. The Gujari are traditionally a migrating pastoral people who live off their herds of sheep, goats, and a few cattle, for which they seek pasture at various elevations.

The Champa, Ladakhi, Balti, and Dard peoples live to the north of the Great Himalaya Range in the Kashmir Himalayas. The Dard speak Indo-European languages, while the others are Tibeto-Burman speakers. The Champa traditionally lead a nomadic pastoral life in the upper Indus valley. The Ladakhi have settled on terraces and alluvial fans that flank the Indus in the northeastern Kashmir region. The Balti have spread farther down the Indus valley and have adopted Islam.

Other Indo-European speakers are the Kanet in Himachal Pradesh and the Khasi in Uttarakhand. In Himachal Pradesh most people in the districts of Kalpa and Lahul-Spiti are the descendants of migrants from Tibet who speak Tibeto-Burman languages.

In Nepal the Pahari, speaking Indo-European languages, constitute the majority of the population, although large groups of Tibeto-Burman speakers are found throughout the country. They include the Newar, the Tamang, the Gurung, the Magar, the Sherpa and other peoples related to the Bhutia, and the Kirat. The Kirat were the earliest inhabitants of the Kathmandu Valley. The Newar are also one of the earliest groups in Nepal. The Tamang inhabit the high valleys to the northwest, north, and east of Kathmandu Valley. The Gurung live on the southern slopes of the Annapurna massif, pasturing their cattle as high as 12,000 feet (3,700 meters). The Magar inhabit western Nepal but migrate seasonally to other parts of the country. The Sherpa, who live to the south of Mount Everest, are famed mountaineers.

For some 200 years the Sikkim region (now a state in India) and the kingdom of Bhutan have been safety valves for the absorption of the excess population of eastern Nepal. More Sherpa now live in the Darjeeling area than in the Mount Everest homeland. At present the Pahari constitute the majority who come from Nepal in both Sikkim and Bhutan. Thus, the people of Sikkim belong to three distinct ethnic groups—the Lepcha, the Bhutia, and the Pahari. Generally speaking, the Nepalese and the Lepcha live in western Bhutan and the Bhutia of Tibetan origin in eastern Bhutan.

Arunachal Pradesh is the homeland of several groups—the Abor or Adi, the Aka, the Apa Tani, the Dafla, the Khampti, the Khowa, the Mishmi, the Momba, the Miri, and the Singpho. Linguistically, they are Tibeto-Burman. Each group has its homeland in a distinct river valley, and all practice shifting cultivation (i.e., they grow crops on a different tract of land each year).

Economy of the Himalayas:

Resources

Economic conditions in the Himalayas partly depend on the limited resources available in different parts of that vast region of varied ecological zones. The principal activity is animal husbandry, but forestry, trade, and tourism are also important. The Himalayas abound in economic resources. Those include pockets of rich arable land, extensive grasslands and forests, workable mineral deposits, easy-to-harness waterpower, and great natural beauty. The most productive arable lands in the western Himalayas are in the Vale of Kashmir, the Kangra valley, the Sutlej River basin, and the terraces flanking the Ganges and Yamuna rivers in Uttarakhand; those areas produce rice, corn (maize), wheat, and millet. In the central Himalayas in Nepal, two-thirds of the arable land is in the foothills and on the adjacent plains; that land yields most of the total rice production of the country. The region also produces large crops of corn, wheat, potatoes, and sugarcane.

Most of the fruit orchards of the Himalayas lie in the Vale of Kashmir and in the Kullu valley of Himachal Pradesh. Fruits such as apples, peaches, pears, and cherries—for which there is a great demand in the cities of India—are grown extensively. On the shores of Dal Lake in Kashmir, there are rich vineyards that produce grapes used to make wine and brandy. On the hills surrounding the Vale of Kashmir grow walnut and almond trees. Bhutan also has fruit orchards and exports oranges to India.

Tea is grown in plantations mainly on the hills and on the plain at the foot of the mountains in the Darjeeling district. Plantations also produce limited amounts of tea in the Kangra valley. Plantations of the spice cardamom are to be found in Sikkim, Bhutan, and the Darjeeling Hills. Medicinal herbs are grown on plantations in areas of Uttarakhand.

Transhumance (the seasonal migration of livestock) is widely practiced in the Himalayan pastures. Sheep, goats, and yaks are raised on the rough grazing lands available. During summer they graze on the pastures at higher elevations, but when the weather turns cold, shepherds migrate with their flocks to lower elevations.

The explosive population growth that has occurred in the Himalayas and elsewhere in the Indian subcontinent since the 1940s has placed great stress on the forests in many areas. Deforestation to clear land for planting and to supply firewood, paper, and construction materials has progressed up steeper and higher slopes of the Lesser Himalayas, triggering environmental degradation. Only in Sikkim and Bhutan are large areas still heavily forested.

The Himalayas are rich in minerals, although exploitation is restricted to the more accessible areas. The Kashmir region has the greatest concentration of minerals. Sapphires are found in the Zanskar Range, and alluvial gold is recovered in the nearby bed of the Indus River. There are deposits of copper ore in Baltistan, and iron ores are found in the Vale of Kashmir. Ladakh possesses borax and sulfur deposits. Coal seams are found in the Jammu Hills. Bauxite also occurs in Kashmir. Nepal, Bhutan, and Sikkim have extensive deposits of coal, mica, gypsum, and graphite and ores of iron, copper, lead, and zinc.

The Himalayan rivers have a tremendous potential for hydroelectric generation. That potential was first harnessed intensively by India beginning in the 1950s. A giant multipurpose project is located at Bhakra-Nangal on the Sutlej River in the Outer Himalayas; its reservoir was completed in 1963 and has a storage capacity of some 348 billion cubic feet (10 billion cubic meters) of water and a total installed generating capacity of 1,050 megawatts. Other Himalayan rivers—including the Kosi, the Gandak (Narayani), and the Jaldhaka—were then harnessed by India, which then supplied electric power to Nepal and Bhutan. Subsequent major projects in India included the Nathpa Jhakri dam on the Sutlej in Himachal Pradesh and, just downstream from that site, the Rampur station, which became operational in 2014. Nepal has also constructed hydropower projects in the Himalayas, as has China, which completed the Zangmu station on the Yarlung Zangbo (Brahmaputra) River in Tibet in 2015.

Tourism has become an increasingly important source of income and employment in parts of the Himalayas, especially Nepal. In addition to sightseers, there has been a dramatic rise in the number of foreign trekkers in the lower mountain elevations, as well as in mountaineers seeking to climb Everest and the other high peaks. The resultant increased traffic and tourists’ heavy consumption of the region’s limited resources, however, have further stressed the regional environment.

Transportation

Trails and footpaths long were the only means of communication in the Himalayas. Although those continue to be important, especially in the more remote locations, road transport now has made the Himalayas accessible from both north and south. In Nepal an east-west highway stretches through the Tarai lowlands, connecting roads that penetrate into many of the country’s mountain valleys. The capital, Kathmandu, is connected to Pokhara by a low Himalayan highway, and another highway through Kodari Pass gives Nepal access to Tibet. A highway running from Kathmandu through Hetaunda and Birganj to Birauni connects Nepal to Bihar state and the rest of India. To the northwest in Pakistan, the Karakoram Highway links that country with China. The Hindustan-Tibet road, which passes through Himachal Pradesh, has been considerably improved; that 300-mile (480-km) highway runs through Shimla, once the summer capital of India, and crosses the Indo-Tibetan border near Shipki Pass. From Manali in the Kullu valley, a highway now crosses not only the Great Himalayas but also the Zanskar Range and reaches Leh in the upper Indus valley. Leh is also connected to India via Srinagar in the Vale of Kashmir; the road from Srinagar to Leh passes over the 17,730-foot- (5,404-meter-) high Khardung Pass—the first of the high passes on the historic caravan trail to Central Asia from India. Many other new roads have been built since 1950.

From the Indian state of Punjab the only direct approach to the Vale of Kashmir is by the highway from Jalandhar to Srinagar (summer capital of Jammu and Kashmir union territory) through Pathankot, Jammu, Udhampur, Banihal, and Khahabal. It crosses the Pir Panjal Range through a tunnel at Banihal. The old road from Rawalpindi, Pakistan, to Srinagar lost its importance with the closing of the road at the line of control between the sectors of Kashmir administered by India and Pakistan.

The Sikkim Himalayas command the historic Kalimpang-to-Lhasa caravan trade route, which passes through Gangtok. Before the mid-1950s there was only one 30-mile (50-km) motorable highway running between Gangtok and Rangpo, on the Tista River, which then continued southward another 70 miles (110 km) to Siliguri (Shiliguri) in West Bengal state. Since then, several roads passable by four-wheel-drive vehicles have been built in the southern part of Sikkim, and the highway from Siliguri has been extended through Lachung, in northern Sikkim, to Tibet.

Only two main railroads, both of narrow gauge, penetrate into the Lesser Himalayas from the plains of India: one in the western Himalayas, between Kalka and Shimla, and the other in the eastern Himalayas, between Siliguri and Darjeeling. Another narrow-gauge line in Nepal runs some 30 miles from Raxaul in Bihar state, India, to Amlekhganj. Two other short railroads run to the Outer Himalayas—one, the railroad of the Kullu Valley, from Pathankot to Jogindarnagar and the other from Haridwar to Dehra Dun.

There are two major airstrips in the Himalayas, one at Kathmandu and the other at Srinagar; the airport at Kathmandu is served by international as well as regional flights. Besides those, there are also an increasing number of airstrips of local importance in Nepal and other countries in the region that can accommodate small aircraft. Improvements in both air and ground transportation have facilitated the growth of tourism in the Himalayas.

Study and exploration

The earliest journeys through the Himalayas were undertaken by traders, shepherds, and pilgrims. The pilgrims believed that the harder the journey was, the nearer it brought them to salvation or enlightenment; the traders and shepherds, though, accepted crossing passes as high as 18,000 to 19,000 feet (5,500 to 5,800 meters) as a way of life. For all others, however, the Himalayas constituted a formidable and fearsome barrier.

The first known Himalayan sketch map of some accuracy was drawn up in 1590 by Antonio Monserrate, a Spanish missionary to the court of the Mughal emperor Akbar. In 1733 a French geographer, Jean-Baptiste Bourguignon d’Arville, compiled the first map of Tibet and the Himalayan range based on systematic exploration. In the mid-19th century the Survey of India organized a systematic program to measure correctly the heights of the Himalayan peaks. The Nepal and Uttarakhand peaks were observed and mapped between 1849 and 1855. Nanga Parbat, as well as the peaks of the Karakoram Range to the north, were surveyed between 1855 and 1859. The surveyors did not assign individual names to the innumerable peaks observed but designated them by letters and Roman numerals. Thus, at first Mount Everest was simply labeled as “H”; that had been changed to Peak XV by 1850. In 1865 Peak XV was renamed for Sir George Everest, surveyor general of India from 1830 to 1843. Not until 1852 were the computations sufficiently advanced for it to be realized that Peak XV was higher than any other mountain in the world. By 1862 more than 40 peaks with elevations exceeding 18,000 feet (5,500 meters) had been climbed for surveying purposes.

In addition to the surveying expeditions, various scientific studies of the Himalayas were conducted in the 19th century. Between 1848 and 1849 the English botanist Joseph Dalton Hooker made a pioneering study of the plant life of the Sikkim Himalayas. He was followed by numerous others, including (in the early 20th century) the British naturalist Richard W.G. Hingston, who wrote valuable accounts of the natural history of animals living at high elevations in the Himalayas.

After World War II the Survey of India prepared some large-scale maps of the Himalayas from aerial photographs. Parts of the Himalayas were also mapped by German geographers and cartographers, with the help of ground photogrammetry. In addition, satellite reconnaissance has been employed to produce even more accurate and detailed maps. Aerial photographs have been used in conjunction with other scientific observation methods to monitor the effects of climate change on the Himalayan environment—notably the recession of glaciers.

Himalayan mountaineering began in the 1880s with the Briton W.W. Graham, who claimed to have climbed several peaks in 1883. Though his reports were received with skepticism, they did spark interest in the Himalayas among other European climbers. In the early 20th century the number of mountaineering expeditions increased markedly to the Karakoram Range and to the Kumaun and Sikkim Himalayas. Between World Wars I and II, a certain national preference developed for the various peaks: the Germans concentrated on Nanga Parbat and Kanchenjunga, the Americans on K2 (in the Karakorams), and the British on Mount Everest. Attempts at scaling Everest began in 1921, and about a dozen of them were undertaken before it was first successfully scaled in May 1953 by the New Zealand mountaineer Edmund Hillary and his Tibetan partner Tenzing Norgay. That same year an Austro-German team led by Karl Maria Herrligkoffer reached the summit of Nanga Parbat.

As the high peaks were conquered one by one, climbers began to look for greater challenges to test their skills and equipment. Some attempted to reach the summits by increasingly difficult routes, while others climbed with minimal amounts of gear or without the use of supplemental oxygen at the highest elevations. Easier access to the mountains brought increasingly large numbers of climbers and hikers into the region—hundreds alone trying to summit Everest each year. By the late 20th and early 21st centuries, the annual number of mountaineering expeditions and tourist excursions to the Himalayas was so large that in some areas the participants were threatening the delicate environmental balance of the mountains by destroying plant and animal life and by leaving behind a growing quantity of refuse. In addition, more people in such a highly dangerous environment invited disaster, as was the case in 2014, when more than 40 foreign trekkers perished in a snowstorm near Annapurna.

2430) George Beadle

Gist:

Work

Organisms' metabolism–the chemical processes within its cells–are regulated by substances called enzymes. George Beadle and Edward Tatum proved in 1941 that our genetic code‚ our genes, govern the formation of enzymes. They exposed a type of mold to x-rays, causing mutations, or changes in its genes. They later succeeded in proving that this led to definite changes in enzyme formation. The conclusion was that each enzyme corresponds to a particular gene.

Summary

George Wells Beadle (born Oct. 22, 1903, Wahoo, Neb., U.S.—died June 9, 1989, Pomona, Calif.) was an American geneticist who helped found biochemical genetics when he showed that genes affect heredity by determining enzyme structure. He shared the 1958 Nobel Prize for Physiology or Medicine with Edward Tatum and Joshua Lederberg.

After earning his doctorate in genetics from Cornell University (1931), Beadle went to the laboratory of Thomas Hunt Morgan at the California Institute of Technology, where he did work on the fruit fly, Drosophila melanogaster. Beadle soon realized that genes must influence heredity chemically.

In 1935, with Boris Ephrussi at the Institut de Biologie Physico-Chimique in Paris, he designed a complex technique to determine the nature of these chemical effects in Drosophila. Their results indicated that something as apparently simple as eye colour is the product of a long series of chemical reactions and that genes somehow affect these reactions.

After a year at Harvard University, Beadle pursued gene action in detail at Stanford University in 1937. Working there with Tatum, he found that the total environment of a red bread mold, Neurospora, could be varied in such a way that the researchers could locate and identify genetic changes, or mutants, with comparative ease. They exposed the mold to X rays and studied the altered nutritional requirements of the mutants thus produced. These experiments enabled them to conclude that each gene determined the structure of a specific enzyme that, in turn, allowed a single chemical reaction to proceed. This “one gene–one enzyme” concept won Beadle and Tatum (with Lederberg) the Nobel Prize in 1958.

In addition, the use of genetics to study the biochemistry of microorganisms, outlined in the landmark paper “Genetic Control of Biochemical Reactions in Neurospora” (1941), by Beadle and Tatum, opened up a new field of research with far-reaching implications. Their methods immediately revolutionized the manufacture of penicillin and provided insights into many biochemical processes.

In 1946 Beadle became professor and chairman of the biology division at the California Institute of Technology and served there until 1960, when he was invited to succeed R. Wendel Harrison as chancellor of the University of Chicago; the title of president was reassigned to the position a year later. He retired from the university to direct (1968–70) the American Medical Association’s Institute for Biomedical Research.

His major works include An Introduction to Genetics (1939; with A.H. Sturtevant), Genetics and Modern Biology (1963), and The Language of Life (1966; with Muriel M. Beadle).

Details

George Wells Beadle (October 22, 1903 – June 9, 1989) was an American geneticist. In 1958 he shared one-half of the Nobel Prize in Physiology or Medicine with Edward Tatum for their discovery of the role of genes in regulating biochemical events within cells. He served as the 7th president of the University of Chicago from 1961 to 1968.

Beadle and Tatum's key experiments involved exposing the bread mold Neurospora crassa to x-rays, causing mutations. In a series of experiments, they showed that these mutations caused changes in specific enzymes involved in metabolic pathways. These experiments led them to propose a direct link between genes and enzymatic reactions, known as the One gene-one enzyme hypothesis.

Education and early life

George Wells Beadle was born in Wahoo, Nebraska. He was the son of Chauncey Elmer Beadle and Hattie Albro, who owned and operated a 40-acre (160,000 sq m) farm nearby.[9] George was educated at the Wahoo High School and might himself have become a farmer if one of his teachers at school had not directed his mind towards science and persuaded him to go to the College of Agriculture in Lincoln, Nebraska. In 1926 he earned his Bachelor of Science degree at the University of Nebraska and subsequently worked for a year with Professor F.D. Keim, who was studying hybrid wheat. In 1927 he earned his Master of Science degree, and Professor Keim secured for him a post as Teaching Assistant at Cornell University, where he worked, until 1931, with Professors R.A. Emerson and L.W. Sharp on Mendelian asynapsis in Zea mays. For this work he obtained, in 1931, his Doctor of Philosophy degree.

Career and research

In 1931 Fellowship at the California Institute of Technology at Pasadena, where he remained from 1931 until 1936. During this period he continued his work on Indian corn and began, in collaboration with Professors Theodosius Dobzhansky, S. Emerson, and Alfred Sturtevant, work on crossing-over in the fruit fly, Drosophila melanogaster.

In 1935 Beadle visited Paris for six months to work with Professor Boris Ephrussi at the Institut de Biologie physico-chimique. Together they began the study of the development of eye pigment in Drosophila which later led to the work on the biochemistry of the genetics of the fungus Neurospora for which Beadle and Edward Lawrie Tatum were together awarded the 1958 Nobel Prize for Physiology or Medicine.

In 1936 Beadle left the California Institute of Technology to become Assistant Professor of Genetics at Harvard University. A year later he was appointed Professor of Biology (Genetics) at Stanford University and there he remained for nine years, working for most of this period in collaboration with Tatum. This work of Beadle and Tatum led to an important generalization. This was that most mutants unable to grow on minimal medium, but able to grow on “complete” medium, each require addition of only one particular supplement for growth on minimal medium. If the synthesis of a particular nutrient (such as an amino acid or vitamin) was disrupted by mutation, that mutant strain could be grown by adding the necessary nutrient to the minimal medium. This finding suggested that most mutations affected only a single metabolic pathway. Further evidence obtained soon after the initial findings tended to show that generally only a single step in the pathway is blocked. Following their first report of three such auxotroph mutants in 1941, Beadle and Tatum used this method to create series of related mutants and determined the order in which amino acids and some other metabolites were synthesized in several metabolic pathways. The obvious inference from these experiments was that each gene mutation affects the activity of a single enzyme. This led directly to the one gene-one enzyme hypothesis, which, with certain qualifications and refinements, has remained essentially valid to the present day. As recalled by Horowitz, the work of Beadle and Tatum also demonstrated that genes have an essential role in biosynthesis. At the time of the experiments (1941), non-geneticists still generally believed that genes governed only trivial biological traits, such as eye color, and bristle arrangement in fruit flies, while basic biochemistry was determined in the cytoplasm by unknown processes. Also, many respected geneticists thought that gene action was far too complicated to be resolved by any simple experiment. Thus Beadle and Tatum brought about a fundamental revolution in our understanding of genetics.

In 1946 Beadle returned to the California Institute of Technology as Professor of Biology and Chairman of the Division of Biology. Here he remained until January 1961 when he was elected Chancellor of the University of Chicago and, in the autumn of the same year, President of this university.

After retiring, Beadle undertook a remarkable experiment in maize genetics. In several laboratories he grew a series of Teosinte/Maize crosses. Then he crossed these progeny with each other. He looked for the rate of appearance of parent phenotypes among this second generation. The vast majority of these plants were intermediate between maize and Teosinte in their features, but about 1 in 500 of the plants were identical to either the parent maize or the parent teosinte. Using the mathematics of Mendelian genetics, he calculated that this showed a difference between maize and teosinte of about 5 or 6 genetic loci. This demonstration was so compelling that most scientists now agree that Teosinte is the wild progenitor of maize.

During his career, Beadle received many honors. These included honorary Doctor of Science degrees from Yale (1947), Nebraska (1949), Northwestern University (1952), Rutgers University (1954), Kenyon College (1955), Wesleyan University (1956), the University of Birmingham and the University of Oxford, England (1959), Pomona College (1961), and Lake Forest College (1962). In 1962 he was also given the honorary degree of LL.D. by the University of California, Los Angeles. He was elected a Fellow of the American Academy of Arts and Sciences in 1946.[15] He also received the Lasker Award of the American Public Health Association (1950), the Dyer Award (1951), the Emil Christian Hansen Prize of Denmark (1953), the Albert Einstein Commemorative Award in Science (1958), the Nobel Prize in Physiology or Medicine 1958 with Edward Tatum and Joshua Lederberg, the National Award of the American Cancer Society (1959), and the Kimber Genetics Award of the National Academy of Sciences (1960).

Hi,

Good work!

2703.

Hi,

#10741. What does the term in Biology Founder effect mean?

#10742. What does the term in Biology Fungus mean?

Hi,

#2565. What does the medical term Hyperbaric medicine mean?

Hi,

#6344.