sheep, common name for many species of wild and domesticated ruminant mammals of the genus Ovis of the Bovidae, or cattle, family. The male is called a ram (if castrated it is a wether), the female is called a ewe, and their offspring is a lamb. Wild sheep, found in mountainous parts of Asia, North America, and the Mediterranean region, are agile rock climbers with large, spiraling horns. They do not bear wool. Among those species are the Asian argali, the Barbary sheep, or aoudad, of North Africa, and the North American bighorn, or Rocky Mountain sheep, found from Alaska to Mexico. Sheep were first domesticated c.7,000 years ago, and the first use of their fleeces for wool is dated at c.4000 B.C. Descendants of Roman flocks figured in the evolution of the Merino type in Spain. The present-day breeds of domesticated sheep—which vary greatly because they were developed for different purposes and environments—are all thought to be derived chiefly from the wild mouflon of Sardinia and Corsica and from the urial of Asia. Sheep are bred for their wool, meat (mutton or lamb, according to age), skins, and, in certain parts of Europe and the Middle East, their milk, from which cheese is made. They are found mostly in temperate climates and thrive on roughages. Most sheep mate in the fall, and the lambs, born five months later, are called spring lambs. Among the important breeds are the Columbia, Cotswold, Dorset, Hampshire, Karakul, Leicester, Lincoln, Merino, Oxford, Rambouillet, Shropshire, Southdown, and Suffolk sheep. Sheep are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Artiodactyla, family Bovidae.

or lambkill

Open upright woody shrub (Kalmia angustifolia) of the heath family. Growing 1–4 ft (0.3–1.2 m) high, it has glossy, leathery, evergreen leaves and showy pink to rose flowers. Like other Kalmia species (including mountain laurel) and other members of the heath family, it contains a poison (andromedotoxin). In northwestern North America, where these plants occur, livestock (especially sheep) that graze on nonfertile soils of abandoned pastures and meadows may ingest enough of the plant to become poisoned, potentially fatally.

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Ruminants (bovid genus Ovis) that have scent glands in the face and hind feet. Horns, if present, are more divergent than those of goats. Species range from 80 to 400 lb (35 to 180 kg). The coat of wild species consists of outer hair underlain by wool. Sheep graze in flocks, preferably on short, fine grasses and legumes. They have been domesticated from at least 5000 BC in the Middle East, Europe, and Central Asia. Most domesticated breeds produce fine wool; the few that produce only hair or coarse or long wool are generally raised for meat. The flesh of mature sheep is called mutton; that of immature sheep is called lamb.

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or mountain sheep

Stocky, climbing hoofed mammal (Ovis canadensis) of western North America. Both sexes have horns that in the male may curve in a spiral more than 39 in. (1 m) long. Their fur is usually brown with a whitish rump patch. The related thinhorn, or Dall's sheep (O. dalli), of Alaska and Canada is similar to the bighorn. Both species are about 39 in. (1 m) tall at the shoulder, but the bighorn is heavier, weighing up to 300 lb (136 kg). They live in small groups among remote crags and cliffs of mountainous areas and feed mainly on grasses. Bighorn rams compete for females by launching themselves at each other from a few yards' distance and clashing horns.

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Mountain range, southern Montana and northern Wyoming, U.S. It is a range of the northern Rocky Mountains extending 120 mi (193 km), rising abruptly 4,000–5,000 ft (1,200–1,500 m) above the Great Plains and Bighorn Basin. The highest summit is Wyoming's Cloud Peak, at 13,165 ft (4,013 m). Bighorn National Forest covers part of the range. On Medicine Mountain is the Medicine Wheel, a prehistoric stone-spoked circle 70 ft (20 m) in diameter.

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Dolly was a ewe (July 5, 1996 – February 14, 2003) that was the first animal to be cloned from an adult somatic cell, using the process of nuclear transfer. She was cloned by Ian Wilmut, Keith Campbell and colleagues at the Roslin Institute in Edinburgh, Scotland. She was born on July 5, 1996 and she lived until the age of six, and was dubbed "the world's most famous sheep" by Scientific American,

The cell used as the donor for the cloning of Dolly was taken from a mammary gland, and the production of a healthy clone therefore proved that a cell taken from a specific body part could recreate a whole individual. More specifically, the production of Dolly showed that mature differentiated somatic cells in an adult animal's body could under some circumstances revert back to an undifferentiated pluripotent form and then develop into any part of an animal. As Dolly was cloned from part of a mammary gland, she was named after the famously busty country western singer Dolly Parton.

Birth

This used the technique of Somatic cell nuclear transfer, where the cell nucleus from an adult cell is transferred into an unfertilized oocyte (developing egg cell) that has had its nucleus removed. The hybrid cell is then stimulated to divide by an electric shock, and when it develops into a blastocyst it is implanted in a surrogate mother.

In the previous year, the same team had produced cloned sheep from the embryonic cells, but this was not seen as a breakthrough since adult cloned animals had been produced from embryonic tissue as long ago as 1958, using cells from the frog Xenopus laevis.

Dolly was the first clone produced from a cell taken from an adult animal. However, this cloning process is still highly inefficient, with Dolly the only lamb that survived to adulthood from 277 attempts. She is also recognised as one of the major stepping stones in the development of modern biology. Wilmut, who led the team that created Dolly, announced in 2007 that the nuclear transfer technique may never be sufficiently efficient for use in humans.

Life

Dolly lived for her entire life at the Roslin Institute. There she was bred with a Welsh Mountain ram and produced six lambs in total. Her first lamb called Bonnie, was born in April 1998. The next year Dolly produced twin lambs Sally and Rosie, and she gave birth to triplets Lucy, Darcy and Cotton in the year after that. In the autumn of 2001, at the age of five, Dolly developed arthritis and began to walk stiffly, but this was successfully treated with anti-inflammatory drugs.

Death

On February 14, 2003, Dolly was euthanised because of a progressive lung disease. A Finn Dorset such as Dolly has a life expectancy of around 11 to 12 years, but Dolly lived to be only six years of age. A post-mortem examination showed she had a form of lung cancer called Jaagsiekte that is a fairly common disease of sheep and is caused by the retrovirus JSRV. Roslin scientists stated that they did not think there was a connection with Dolly's being a clone, and that other sheep in the same flock had died of the same disease. Such lung diseases are a particular danger for sheep kept indoors, and Dolly had to sleep inside for security reasons.

However, some have speculated that a contributing factor to Dolly's death was that she could have been born with a genetic age of six years, the same age as the sheep from which she was cloned. One basis for this idea was the finding that Dolly's telomeres were short, which typically is a result of the aging process. However, the Roslin Institute have stated that intensive health screening did not reveal any abnormalities in Dolly that could have come from advanced aging.

Legacy

After cloning was successfully demonstrated through the production of Dolly, many other large mammals have been cloned, including horses and bulls. The attempt to clone argali sheep did not produce viable embryos. The attempt to clone a banteng bull was more successful, as were the attempts to clone mouflon (a form of wild sheep), both resulting in viable offspring. In 2005 a dog, Snuppy, was cloned by Korean stem cell researcher, Hwang Woo-Suk.

Cloning may eventually become a viable tool for preserving endangered species and could be important in the future production of transgenic livestock. However, animal conservation professionals point out that cloning does not alleviate the problems of loss of genetic diversity (see inbreeding) and habitat, and so must be considered an experimental technology for the time being, and all in all would only rarely be worth the cost, which on a per-individual basis far exceeds conventional techniques such as captive breeding or embryo transfer.

References

External links

• Dolly the Sheep, 1996-2000 from the Science Museum, London
• Cloning - A life of Dolly from the Roslin Institute.
• Animal cloning & Dolly
• Image library Photos of Dolly and other cloned animals at the Roslin Institute.