Jacob (sheep)
Encyclopedia
The Jacob sheep is a rare breed
of small, piebald
(colored with white spots), polycerate (multi-horned) sheep. Jacobs may have from two to six horns
, but most commonly have four. The most common color is black and white, but they may also be blue and white or lilac and white in coloring. Jacobs are usually raised for their wool
, meat, and hides. They are also kept as pets and ornamental animals, and have been used as guard animals
to protect farm property from theft or vandalism and defend other livestock
against predator
s.
Generally referred to as an unimproved or heirloom breed (one that has survived with little human selection
), the Jacob is descended from an ancient Old World
breed of sheep, although its exact origins remain unclear. Spotted polycerate sheep were documented in England by the mid–17th century, and were widespread a century later. Unlike most other old world breeds, the Jacobs of North America have not undergone extensive cross-breeding
and selective breeding
; their body habitus resembles that of a goat
. Relative to their American counterparts, British Jacobs tend to be larger and heavier, and have lost many of their original characteristics through artificial selection
.
, Middle East
, and Mediterranean
regions. A piebald breed of sheep probably existed in the Levant
, specifically in the area that is now known as Syria
, about three thousand years ago.
Among the many accounts of ancient breeds of piebald sheep is the story of Jacob
from the first book of the Hebrew Bible
and the Christian Old Testament
. According to the Book of Genesis (Genesis 30:31–43), in what may be the earliest recorded attempt at selective breeding, Jacob took every speckled and spotted sheep from his father-in-law's (Laban's
) flock and bred them. The Jacob is named for the Biblical figure of Jacob. The resulting breed may have accompanied the westward expansion of human civilization through Northern Africa, Sicily, Spain and eventually England. However, it was not until the 20th century when the breed acquired the name "Jacob sheep".
A limited amount of circumstantial evidence
from the historical record lends support to a related theory that the Jacob is a descendant of the fat-tailed sheep
, another ancient breed from Mesopotamia
. The earliest records of the fat-tailed sheep are found in the Sumer
ian cities of ancient Uruk
(3000 BC) and Ur
(2400 BC) on stone vessels and mosaic
s. Another early reference to this breed is found in the Book of Leviticus (Leviticus 3:9), where an animal sacrifice
is described which includes the tail fat of sheep. Despite the scant evidence from the historical record, a recent genetic analysis
has provided compelling evidence supporting a direct link between the Jacob and certain unimproved breeds in Southwest Asia and Africa rather than other British breeds. Using retrovirus
es as genetic marker
s, the authors found that sheep dispersed across Eurasia
and Africa via at least two separate migratory episodes. Descendants of the first migrations include the Mouflon
, as well as other unimproved breeds, such as the North Ronaldsay sheep, Soay sheep
, and the northern European short-tailed sheep
. A later migratory episode shaped the great majority of present-day breeds.
Some people believe that the Jacob is a descendant of a subarctic
breed of sheep introduced by Viking
s to the British Isles
during the Middle Ages
. Norsemen
are believed to have introduced certain robust types of sheep to Northern Europe and the British Isles between the late eighth century to the middle of the eleventh century. However, the sheep introduced by the Norse were of a short-tailed variety native to an area stretching from the British Isles to the Baltic
, known as the northern European short-tailed sheep
. In fact, all Scandinavian breeds belong to the Northern European short-tailed group of sheep. The northern European short-tailed sheep are a group of sheep breeds and landrace
s which includes the Finnsheep
, Icelandic
, Romanov
, Shetland
, Spaelsau, and several other breeds. The Jacob bears little resemblance to these. The Jacob is a long-tailed breed, and is therefore unlikely to be related to any breeds introduced by the Vikings.
One persistent legend holds that the Jacob washed ashore from shipwrecks in England after the destruction of the Spanish Armada
in 1588. Despite the fact that there is little if any reliable evidence to support this claim, the Jacob was referred to as the "Spanish sheep" for much of its early recorded history. It has been bred in England for at least 350 years, and spotted sheep were widespread in England by the mid–18th century. By that time, Jacobs were often kept as ornamental animals grazed in parks, which probably kept the breed extant. In recent years, Jacobs have been used as guard sheep in Gloucestershire
, in the manner of guard dog
s, to protect farm property from vandalism.
Jacobs were first imported into parks and zoos of North America in the early 20th century. Some individuals acquired them from zoos in the 1960s and 1970s, but the breed remained rare in America until the 1980s. Most of today’s population of American Jacobs is descended from those imported at that time. The Jacob Sheep Breeders Association (JSBA), organized in 1989, was the first breed association to be established in North America. Jacobs have become popular among small flock holders as well as handspinners and weavers.
(ALBC) of North America and the Rare Breeds Survival Trust
(RBST) of the United Kingdom are responsible for the documentation and preservation of rare breeds of domesticated animals, including the Jacob. There are also several breed registries
whose only focus is the Jacob, such as the American Jacob Sheep Registry and the Jacob Sheep Breeders Association. In the United States, identification of Jacobs as endangered and ensuing registration of sheep began in 1985. As of 2009, the ALBC has listed the American population of the Jacob as a "threatened
breed" and a conservation priority. The breed is estimated to have fewer than 1,000 annual registrations in the United States and a global population of less than 5,000. Identifying purebreds is a continual challenge for American breeders, and the marketing of crossbreeds (such as the Jacob-Dorset) as purebred
Jacobs to unsuspecting buyers has presented a significant obstacle to the conservation of the American population. However, the RBST in the United Kingdom do not view the Jacob as being at risk as there are in excess of 3,000 registered breeding females.
, Icelandic
, Manx Loaghtan
, and the Navajo-Churro
, and other piebald breeds include the Finnsheep
and the West African Dwarf
.
Mature rams (males) weigh about 120 to 180 lb (54.4 to 81.6 kg), while ewes (females) weigh about 80 to 120 lb (36.3 to 54.4 kg). The body frame is long, with a straight back and a rump
that slopes toward the base of the tail. The rams have short scrotum
s free of wool which hold the testicles closer to the body than those of modern breeds, while the ewes have small udder
s free of wool that are also held closer to the body than those of modern breeds. The head is slender and triangular, and clear of wool forward of the horns and on the cheeks. The tail is long and woolly, extending almost to the hock if it has not been docked
. Jacob owners do not usually dock the tail completely, even for market sheep, but instead leave several inches to cover the anus and vulva. The legs are medium-length, slender, free of wool below the knees, and preferably white with or without colored patches. The hooves are black or striped. It is not unusual for Jacobs to be cow-hocked
. They provide a lean carcass with little external fat, with a high yield of meat compared to more improved breeds.
The most distinguishing features of the Jacob are their four horns, although they may have as few as two or as many as six. Both sexes are always horned, and the rams tend to have larger and more impressive horns. Two-horned rams typically have horizontal double-curled horns. Four-horned rams have two vertical center horns which may be two or more feet in length, and two smaller side horns, which grow down along the sides of the head. The horns on the ewe are smaller in diameter, shorter in length and appear more delicate than those of the ram. British Jacobs most often have two horns, while American Jacobs are more often polycerate. Polled
(hornless) sheep are not registrable, since this trait is considered an indication of past cross-breeding, and as such there is no such thing as a polled purebred Jacob.
The horns are normally black, but may be black and white striped; white horns are undesirable. Ideally, horns are smooth and balanced, strongly attached to the skull, and grow in a way that does not impede the animal's sight or grazing
abilities. Rams have larger horns than ewes. The horns in two-horned sheep, and the lower horns in four-horned animals, grow in a spiral shape. The rostral set of horns usually extend upwards and outwards, while the caudal set of horns curls downwards along the side of the head and neck. On polycerate animals it is preferred that there is a fleshy gap between the two pairs of horns. Partial or deformed horns that are not firmly attached to the skull, often referred to as "scurs", are not unusual but are considered undesirable.
The multihorned trait is genetically linked
to a condition known as split eyelid. In mild cases the eyelid shows a "peak" but does not impair vision or cause discomfort. Extreme cases (Grade 3 or higher) result in a complete separation of the upper eyelid in the middle, and these sheep should not be used for breeding.
Breed specific markings include large, symmetrical dark patches incorporating the ears, eyes and cheeks, and a dark cape
over the dorsal part of the neck and shoulders. The face should have a white blaze extending from the poll to the muzzle
. The muzzle itself should be dark. The classic Jacob face is often referred to as "badger-faced", consisting of black cheeks and muzzle with a white blaze running down the front of the face. In addition to these markings, random spots may occur on the rest of the body and legs (including the carpi
, hocks, and pastern
s). Certain markings are common in particular lines: large muzzle markings, lack of leg markings, lack of muzzle markings, etc.
While other British and Northern European multi-horned sheep have a fine inner coat and a coarse, longer outer coat, Jacobs have a medium grade fleece and no outer coat. The grade of Jacob wool is of a spinning count
(S number
or Bradford count
) of 46–54, which corresponds to an average fiber diameter of about 32.7–27.9 micrometers
, or Low 1/4 Blood–1/4 Blood on the American or Blood grading system. Lambs of the more primitive lines are born with a coat of guard hair that is protective against rain and cold; this birth coat is shed at 3–6 months.
In general, the fleece is light, soft, springy and open, with little lanolin
(grease). The fleece generally weighs 3 to 6 lb (1.4 to 2.7 kg) and varies in crimp and fineness. Staple length is generally 3 to 5 in (7.6 to 12.7 cm) and may be up to 7 inches (17.8 cm). Similar to other unimproved breeds, most Jacobs have some white, kinky, kemp
(coarse wool) in their fleece, though excessive kemp is undesirable. In some sheep (particularly British Jacobs, which have denser fleeces), the black wool will grow longer or shorter than the white wool. This is called "quilted fleece" and is an undesirable trait.
Jacobs are shorn
once a year, most often in the springtime
. Some individual sheep may develop a natural "break," or marked thinning, of the fleece in springtime, which can lead to a natural shedding of the fleece, particularly around the neck and shoulders. The medium-fine grade wool has a high luster, and is highly sought after by handspinners if it is free of kemp. The colors may be separated or blended after shearing and before spinning to produce various shades of yarn from a single fleece, from nearly white to nearly black. Tanned pelts also command high market prices.
The Jacob is generally considered to be an "unimproved" or "heirloom" breed (one that has survived with little human selection). Such breeds have been left to mate amongst themselves, often for centuries, and therefore retain much of their original wildness and physical characteristics. American breeders have not subjected Jacobs to extensive cross-breeding or selective breeding, other than for fleece characteristics. Like other unimproved breeds, significant variability is present among individuals within a flock. In contrast, the British Jacob has been selected for greater productivity of meat, and therefore tends to be larger, heavier and have a more uniform appearance. As a result, the American Jacob has retained nearly all of the original phenotypic
characteristics of its Old World ancestors while its British counterpart has lost many of its unimproved physical characteristics through cross-breeding and selective breeding. The British Jacob has thus diverged
from the American Jacob as a result of artificial selection.
Jacobs are typically hardy, low-maintenance animals with a naturally high resistance to parasites
and hoof problems. Jacobs do not show much flocking behavior
. They can be skittish
if not used to people, although with daily handling they will become tame
and make good pet
s. They require shelter from extreme temperatures, but the shelter can be open and simple. They tend to thrive in extremes of heat and cold and have good or excellent foraging
capabilities. They can secure adequate nutrition with minimal to no supplementation, even in the presence of suboptimal soil conditions.
Due to their low tail dock and generally unimproved anatomy, Jacob ewes are widely reputed to be easy-lambing. Jacobs are seasonal breeder
s, with ewes generally cycling in the cooler months of the fall. They will begin to cycle during the first fall following their birth and most often the ewe's first lamb is a single. Subsequent gestations
will typically bear one or two lambs in the spring, and triplets are not unusual. The lambs will exhibit their spotting and horn characteristics at birth, with the horn buds more readily apparent on ram lambs. Lambs may be weaned at two months of age, but many shepherds do not separate lambs and allow the ewe to wean the lamb at about 4 months of age. Jacob ewes are instinctively attentive mothers and are protective of their lambs. They are included in commercial flocks in England because of their ease of lambing and strong mothering instincts.
s in humans known as lysosomal storage disease
s. It is caused by a deficiency of hexosaminidase A
, an enzyme
involved in the hydrolysis
of GM2 ganglioside
. This enzyme deficiency is caused by a mutation
on the HEXA
gene on chromosome 15
. An autosomal
recessive disease, Tay–Sachs is characterized by progressive deterioration of mental and physical abilities
, usually resulting in death by the age of four years.
Recent research has revealed that this disease exists in some flocks of Jacob sheep. Four Jacob lambs from St. Jude's Farm in Lucas, Texas
were examined for an unusual, progressive and ultimately fatal neurologic disease. Clinical findings included ataxia
in all 4 limbs, proprioceptive
deficits, and cortical blindness
. The diagnosis of GM2 gangliosidosis
was confirmed by biochemical
and molecular genetic
studies. Furthermore, the biochemical mechanism for this disease in the Jacob (diminished activity of hexosaminidase A resulting in increased concentrations of GM2 ganglioside) is virtually identical to that observed in humans. Sequencing
of the cDNA
of the HEXA gene of affected Jacobs reveals an identical number of nucleotide
s and exon
s as in the human HEXA gene, and 86% identity in nucleotide sequence. A missense mutation
(now referred to as the G444R mutation) was found in the HEXA cDNA of the affected sheep caused by a single nucleotide change at the end of exon 11, resulting in the skipping of exon 11. This model of Tay–Sachs disease provided by the Jacob is the first to offer promise as a means for trials of gene therapy
, which may eventually prove to be useful in the treatment of the disease in humans.
Bai Zeng and Paola Torres of the Department of Neurology at New York University School of Medicine
examined DNA samples of 443 Jacobs from various flocks within the United States. 51 of these specimens were identified as carriers
of the G444R mutation (a carrier incidence of 11%); 90% of the flocks were found to have one or more mutation carriers. Either Jacob parent can carry the mutant autosomal recessive gene. Carriers appear normal and live a normal life. Turner 183K, a bloodline foundation
ram and the apparent source of the mutation in North America, was born of imported Jacobs. The primary suspect is Turner’s mother. The identification of this type of genetic defect in a foundation ram is particularly concerning because in North America, the Jacob is considered to be a bottleneck breed
representing a very small gene pool
.
Rare breed (agriculture)
A rare breed is defined as a breed of livestock or poultry that is not common in modern agriculture, though it may have been in the past. Various national and international organizations, such as the UN Food and Agriculture Organization, the American Livestock Breeds Conservancy or the Rare Breeds...
of small, piebald
Piebald
A piebald or pied animal is one that has a spotting pattern of large unpigmented, usually white, areas of hair, feathers, or scales and normally pigmented patches, generally black. The colour of the animal's skin underneath its coat is also pigmented under the dark patches and unpigmented under...
(colored with white spots), polycerate (multi-horned) sheep. Jacobs may have from two to six horns
Horn (anatomy)
A horn is a pointed projection of the skin on the head of various animals, consisting of a covering of horn surrounding a core of living bone. True horns are found mainly among the ruminant artiodactyls, in the families Antilocapridae and Bovidae...
, but most commonly have four. The most common color is black and white, but they may also be blue and white or lilac and white in coloring. Jacobs are usually raised for their wool
Wool
Wool is the textile fiber obtained from sheep and certain other animals, including cashmere from goats, mohair from goats, qiviut from muskoxen, vicuña, alpaca, camel from animals in the camel family, and angora from rabbits....
, meat, and hides. They are also kept as pets and ornamental animals, and have been used as guard animals
Guard llama
A guard llama is a llama used in farming to protect sheep, alpacas, goats or other livestock from coyotes, dogs and other predators. Typically, a single gelded male is used.-Guarding:...
to protect farm property from theft or vandalism and defend other livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...
against predator
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
s.
Generally referred to as an unimproved or heirloom breed (one that has survived with little human selection
Selective breeding
Selective breeding is the process of breeding plants and animals for particular genetic traits. Typically, strains that are selectively bred are domesticated, and the breeding is sometimes done by a professional breeder. Bred animals are known as breeds, while bred plants are known as varieties,...
), the Jacob is descended from an ancient Old World
Old World
The Old World consists of those parts of the world known to classical antiquity and the European Middle Ages. It is used in the context of, and contrast with, the "New World" ....
breed of sheep, although its exact origins remain unclear. Spotted polycerate sheep were documented in England by the mid–17th century, and were widespread a century later. Unlike most other old world breeds, the Jacobs of North America have not undergone extensive cross-breeding
Crossbreed
A crossbreed or crossbred usually refers to an animal with purebred parents of two different breeds, varieties, or populations. Crossbreeding refers to the process of breeding such an animal, often with the intention to create offspring that share the traits of both parent lineages, or producing...
and selective breeding
Selective breeding
Selective breeding is the process of breeding plants and animals for particular genetic traits. Typically, strains that are selectively bred are domesticated, and the breeding is sometimes done by a professional breeder. Bred animals are known as breeds, while bred plants are known as varieties,...
; their body habitus resembles that of a goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...
. Relative to their American counterparts, British Jacobs tend to be larger and heavier, and have lost many of their original characteristics through artificial selection
Artificial selection
Artificial selection describes intentional breeding for certain traits, or combination of traits. The term was utilized by Charles Darwin in contrast to natural selection, in which the differential reproduction of organisms with certain traits is attributed to improved survival or reproductive...
.
History
The origins of the Jacob are obscure, but it is certainly a very old breed. Piebald sheep have been described throughout history, appearing in works of art from the Far EastFar East
The Far East is an English term mostly describing East Asia and Southeast Asia, with South Asia sometimes also included for economic and cultural reasons.The term came into use in European geopolitical discourse in the 19th century,...
, Middle East
History of the Middle East
This article is a general overview of the history of the Middle East. For more detailed information, see articles on the histories of individual countries and regions...
, and Mediterranean
History of the Mediterranean region
The history of the Mediterranean region is the history of the interaction of the cultures and people of the lands surrounding the Mediterranean Sea —the central superhighway of transport, trade and cultural exchange between diverse peoples...
regions. A piebald breed of sheep probably existed in the Levant
Levant
The Levant or ) is the geographic region and culture zone of the "eastern Mediterranean littoral between Anatolia and Egypt" . The Levant includes most of modern Lebanon, Syria, Jordan, Israel, the Palestinian territories, and sometimes parts of Turkey and Iraq, and corresponds roughly to the...
, specifically in the area that is now known as Syria
Syria
Syria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the West, Turkey to the north, Iraq to the east, Jordan to the south, and Israel to the southwest....
, about three thousand years ago.
Among the many accounts of ancient breeds of piebald sheep is the story of Jacob
Jacob
Jacob "heel" or "leg-puller"), also later known as Israel , as described in the Hebrew Bible, the Talmud, the New Testament and the Qur'an was the third patriarch of the Hebrew people with whom God made a covenant, and ancestor of the tribes of Israel, which were named after his descendants.In the...
from the first book of the Hebrew Bible
Hebrew Bible
The Hebrew Bible is a term used by biblical scholars outside of Judaism to refer to the Tanakh , a canonical collection of Jewish texts, and the common textual antecedent of the several canonical editions of the Christian Old Testament...
and the Christian Old Testament
Old Testament
The Old Testament, of which Christians hold different views, is a Christian term for the religious writings of ancient Israel held sacred and inspired by Christians which overlaps with the 24-book canon of the Masoretic Text of Judaism...
. According to the Book of Genesis (Genesis 30:31–43), in what may be the earliest recorded attempt at selective breeding, Jacob took every speckled and spotted sheep from his father-in-law's (Laban's
Laban (Bible)
Laban is the son of Bethuel, brother of Rebekah and the father of Leah and Rachel and Bilhah and Zilpah as described in the Book of Genesis. As such he is brother-in-law to Isaac and both father-in-law and uncle to Jacob...
) flock and bred them. The Jacob is named for the Biblical figure of Jacob. The resulting breed may have accompanied the westward expansion of human civilization through Northern Africa, Sicily, Spain and eventually England. However, it was not until the 20th century when the breed acquired the name "Jacob sheep".
A limited amount of circumstantial evidence
Circumstantial evidence
Circumstantial evidence is evidence in which an inference is required to connect it to a conclusion of fact, like a fingerprint at the scene of a crime...
from the historical record lends support to a related theory that the Jacob is a descendant of the fat-tailed sheep
Fat-tailed sheep
The fat-tailed sheep is a general type of domestic sheep known for their distinctive large tails and hindquarters. Fat-tailed sheep breeds comprise approximately 25% of the world sheep population, and are commonly found in northern parts of Africa, the Middle East, Pakistan, North India, Western...
, another ancient breed from Mesopotamia
Mesopotamia
Mesopotamia is a toponym for the area of the Tigris–Euphrates river system, largely corresponding to modern-day Iraq, northeastern Syria, southeastern Turkey and southwestern Iran.Widely considered to be the cradle of civilization, Bronze Age Mesopotamia included Sumer and the...
. The earliest records of the fat-tailed sheep are found in the Sumer
Sumer
Sumer was a civilization and historical region in southern Mesopotamia, modern Iraq during the Chalcolithic and Early Bronze Age....
ian cities of ancient Uruk
Uruk
Uruk was an ancient city of Sumer and later Babylonia, situated east of the present bed of the Euphrates river, on the ancient dry former channel of the Euphrates River, some 30 km east of modern As-Samawah, Al-Muthannā, Iraq.Uruk gave its name to the Uruk...
(3000 BC) and Ur
Ur
Ur was an important city-state in ancient Sumer located at the site of modern Tell el-Muqayyar in Iraq's Dhi Qar Governorate...
(2400 BC) on stone vessels and mosaic
Mosaic
Mosaic is the art of creating images with an assemblage of small pieces of colored glass, stone, or other materials. It may be a technique of decorative art, an aspect of interior decoration, or of cultural and spiritual significance as in a cathedral...
s. Another early reference to this breed is found in the Book of Leviticus (Leviticus 3:9), where an animal sacrifice
Animal sacrifice
Animal sacrifice is the ritual killing of an animal as part of a religion. It is practised by many religions as a means of appeasing a god or gods or changing the course of nature...
is described which includes the tail fat of sheep. Despite the scant evidence from the historical record, a recent genetic analysis
Genetic analysis
Genetic analysis can be used generally to describe methods both used in and resulting from the sciences of genetics and molecular biology, or to applications resulting from this research....
has provided compelling evidence supporting a direct link between the Jacob and certain unimproved breeds in Southwest Asia and Africa rather than other British breeds. Using retrovirus
Retrovirus
A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme. The virus thereafter replicates as part of the host cell's DNA...
es as genetic marker
Genetic marker
A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify cells, individuals or species. It can be described as a variation that can be observed...
s, the authors found that sheep dispersed across Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
and Africa via at least two separate migratory episodes. Descendants of the first migrations include the Mouflon
Mouflon
The mouflon is a subspecies group of the wild sheep Ovis aries. Populations of Ovis aries can be partitioned into the mouflons and urials or arkars...
, as well as other unimproved breeds, such as the North Ronaldsay sheep, Soay sheep
Soay sheep
The Soay sheep is a primitive breed of domestic sheep descended from a population of feral sheep on the island of Soay in the St. Kilda Archipelago, about from the Western Isles of Scotland...
, and the northern European short-tailed sheep
Northern European short-tailed sheep
Northern European short-tailed sheep are a group of sheep breeds and landraces from the British Isles, Scandinavia, and the area around the Baltic. They are thought to be derived from the first sheep brought to Europe by early farmers...
. A later migratory episode shaped the great majority of present-day breeds.
Some people believe that the Jacob is a descendant of a subarctic
Subarctic
The Subarctic is a region in the Northern Hemisphere immediately south of the true Arctic and covering much of Alaska, Canada, the north of Scandinavia, Siberia, and northern Mongolia...
breed of sheep introduced by Viking
Viking
The term Viking is customarily used to refer to the Norse explorers, warriors, merchants, and pirates who raided, traded, explored and settled in wide areas of Europe, Asia and the North Atlantic islands from the late 8th to the mid-11th century.These Norsemen used their famed longships to...
s to the British Isles
British Isles
The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...
during the Middle Ages
Middle Ages
The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...
. Norsemen
Norsemen
Norsemen is used to refer to the group of people as a whole who spoke what is now called the Old Norse language belonging to the North Germanic branch of Indo-European languages, especially Norwegian, Icelandic, Faroese, Swedish and Danish in their earlier forms.The meaning of Norseman was "people...
are believed to have introduced certain robust types of sheep to Northern Europe and the British Isles between the late eighth century to the middle of the eleventh century. However, the sheep introduced by the Norse were of a short-tailed variety native to an area stretching from the British Isles to the Baltic
Baltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...
, known as the northern European short-tailed sheep
Northern European short-tailed sheep
Northern European short-tailed sheep are a group of sheep breeds and landraces from the British Isles, Scandinavia, and the area around the Baltic. They are thought to be derived from the first sheep brought to Europe by early farmers...
. In fact, all Scandinavian breeds belong to the Northern European short-tailed group of sheep. The northern European short-tailed sheep are a group of sheep breeds and landrace
Landrace
A landrace is a local variety of a domesticated animal or plant species which has developed largely by natural processes, by adaptation to the natural and cultural environment in which it lives. It differs from a formal breed which has been bred deliberately to conform to a particular standard...
s which includes the Finnsheep
Finnsheep
The Finnish Landrace or Finnsheep is a breed of domestic sheep which has a high incidence of multiple births – it is common for a ewe to have three, four, or even five lambs at once. In North America there have been several instances of births of seven lambs, and the record in Finland is nine...
, Icelandic
Icelandic sheep
The Icelandic sheep is a breed of domestic sheep. The Icelandic breed is one of the Northern European short-tailed sheep, which exhibit a fluke-shaped, naturally short tail. The Icelandic is a mid-sized breed, generally short legged and stocky, with face and legs free of wool...
, Romanov
Romanov (sheep)
Romanov is a breed of domestic sheep originating from the Upper Volga region in Russia. These domestic sheep got the name Romanov from the town of the same name. In the 18th century, these sheep first got noticed. Soon after they were noticed, they were imported into Germany and then into France...
, Shetland
Shetland (sheep)
The Shetland sheep is a small, fine-woolled breed of sheep originating in the Shetland Isles, but now also kept in many other parts of the world. It is one of the Northern European short-tailed sheep group, and is closely related to the extinct Scottish Dunface. Shetlands are classed as a...
, Spaelsau, and several other breeds. The Jacob bears little resemblance to these. The Jacob is a long-tailed breed, and is therefore unlikely to be related to any breeds introduced by the Vikings.
One persistent legend holds that the Jacob washed ashore from shipwrecks in England after the destruction of the Spanish Armada
Spanish Armada
This article refers to the Battle of Gravelines, for the modern navy of Spain, see Spanish NavyThe Spanish Armada was the Spanish fleet that sailed against England under the command of the Duke of Medina Sidonia in 1588, with the intention of overthrowing Elizabeth I of England to stop English...
in 1588. Despite the fact that there is little if any reliable evidence to support this claim, the Jacob was referred to as the "Spanish sheep" for much of its early recorded history. It has been bred in England for at least 350 years, and spotted sheep were widespread in England by the mid–18th century. By that time, Jacobs were often kept as ornamental animals grazed in parks, which probably kept the breed extant. In recent years, Jacobs have been used as guard sheep in Gloucestershire
Gloucestershire
Gloucestershire is a county in South West England. The county comprises part of the Cotswold Hills, part of the flat fertile valley of the River Severn, and the entire Forest of Dean....
, in the manner of guard dog
Guard dog
A guard dog, an attack dog or watch dog is a dog used to guard against, and watch for, unwanted or unexpected people or animals. The dog is discriminating so that it does not annoy or attack familiar people.-Barking:...
s, to protect farm property from vandalism.
Jacobs were first imported into parks and zoos of North America in the early 20th century. Some individuals acquired them from zoos in the 1960s and 1970s, but the breed remained rare in America until the 1980s. Most of today’s population of American Jacobs is descended from those imported at that time. The Jacob Sheep Breeders Association (JSBA), organized in 1989, was the first breed association to be established in North America. Jacobs have become popular among small flock holders as well as handspinners and weavers.
Conservation status
Conservation charities such as the American Livestock Breeds ConservancyAmerican Livestock Breeds Conservancy
The American Livestock Breeds Conservancy is a nonprofit organization focused on preserving and promoting genetic diversity among rare breeds of livestock...
(ALBC) of North America and the Rare Breeds Survival Trust
Rare Breeds Survival Trust
The Rare Breeds Survival Trust is a conservation charity, whose purpose is to secure the continued existence and viability of the United Kingdom’s native farm animal genetic resources...
(RBST) of the United Kingdom are responsible for the documentation and preservation of rare breeds of domesticated animals, including the Jacob. There are also several breed registries
Breed registry
A breed registry, also known as a stud book or register, in animal husbandry and the hobby of animal fancy, is an official list of animals within a specific breed whose parents are known. Animals are usually registered by their breeders when they are still young...
whose only focus is the Jacob, such as the American Jacob Sheep Registry and the Jacob Sheep Breeders Association. In the United States, identification of Jacobs as endangered and ensuing registration of sheep began in 1985. As of 2009, the ALBC has listed the American population of the Jacob as a "threatened
Threatened species
Threatened species are any speciesg animals, plants, fungi, etc.) which are vulnerable to endangerment in the near future.The World Conservation Union is the foremost authority on threatened species, and treats threatened species not as a single category, but as a group of three categories,...
breed" and a conservation priority. The breed is estimated to have fewer than 1,000 annual registrations in the United States and a global population of less than 5,000. Identifying purebreds is a continual challenge for American breeders, and the marketing of crossbreeds (such as the Jacob-Dorset) as purebred
Purebred
Purebreds, also called purebreeds, are cultivated varieties or cultivars of an animal species, achieved through the process of selective breeding...
Jacobs to unsuspecting buyers has presented a significant obstacle to the conservation of the American population. However, the RBST in the United Kingdom do not view the Jacob as being at risk as there are in excess of 3,000 registered breeding females.
Physical characteristics
General
The Jacob is a small, multi-horned, piebald sheep that resembles a goat in its conformation. However, it is not the only breed that can produce polycerate or piebald offspring. Other polycerate breeds include the HebrideanHebridean (sheep)
The Hebridean is a breed of small black sheep from Scotland, similar to other members of the Northern European short-tailed sheep group, having a short, triangular tail. They often have two pairs of horns...
, Icelandic
Icelandic sheep
The Icelandic sheep is a breed of domestic sheep. The Icelandic breed is one of the Northern European short-tailed sheep, which exhibit a fluke-shaped, naturally short tail. The Icelandic is a mid-sized breed, generally short legged and stocky, with face and legs free of wool...
, Manx Loaghtan
Manx Loaghtan
The Manx Loaghtan is a breed of sheep native to the Isle of Man. It is sometimes spelled as Loaghtyn or Loghtan. It is characterized by a dark brown wool and usually having four or occasionally six horns....
, and the Navajo-Churro
Navajo-Churro sheep
The Navajo-Churro, or Churro for short, is a breed of domestic sheep originating with the Spanish Churra sheep obtained by the Navajo Indian tribe. The breed is renowned for its hardiness and adaptability to extremes of climate. Its wool consists of a protective topcoat and soft undercoat...
, and other piebald breeds include the Finnsheep
Finnsheep
The Finnish Landrace or Finnsheep is a breed of domestic sheep which has a high incidence of multiple births – it is common for a ewe to have three, four, or even five lambs at once. In North America there have been several instances of births of seven lambs, and the record in Finland is nine...
and the West African Dwarf
West African Dwarf (sheep)
West African Dwarf is a domesticated breed of sheep and is the dominant breed from southwest to central Africa. This breed is primarily raised for meat.-Characteristics:...
.
Mature rams (males) weigh about 120 to 180 lb (54.4 to 81.6 kg), while ewes (females) weigh about 80 to 120 lb (36.3 to 54.4 kg). The body frame is long, with a straight back and a rump
Rump (animal)
The rump or croup, in the external morphology of an animal, is the portion of the posterior dorsum that is posterior to the loins and anterior to the tail. Anatomically, the rump corresponds to the sacrum....
that slopes toward the base of the tail. The rams have short scrotum
Scrotum
In some male mammals the scrotum is a dual-chambered protuberance of skin and muscle containing the testicles and divided by a septum. It is an extension of the perineum, and is located between the penis and anus. In humans and some other mammals, the base of the scrotum becomes covered with curly...
s free of wool which hold the testicles closer to the body than those of modern breeds, while the ewes have small udder
Udder
An udder is an organ formed of the mammary glands of female quadruped mammals, especially ruminants such as cattle, goats, sheep and deer. The udder is a single mass hanging beneath the animal, consisting of pairs of mammary glands...
s free of wool that are also held closer to the body than those of modern breeds. The head is slender and triangular, and clear of wool forward of the horns and on the cheeks. The tail is long and woolly, extending almost to the hock if it has not been docked
Docking (animal)
Docking is a term for the intentional removal of part of an animal's tail or ears. The term cropping is also used, though more commonly in reference to the cropping of ears, while docking more commonly—but not exclusively—refers to the tail. The term tailing is also commonly used...
. Jacob owners do not usually dock the tail completely, even for market sheep, but instead leave several inches to cover the anus and vulva. The legs are medium-length, slender, free of wool below the knees, and preferably white with or without colored patches. The hooves are black or striped. It is not unusual for Jacobs to be cow-hocked
Cow-hocked
Cow-hocked is the condition in a livestock animal where the back leg joints of the animal are set incorrectly. This term is used to describe when the back 'knee' on an animal is set inward, resulting in a splayed look in the back legs. This can result in the uneven wearing of hooves, which can end...
. They provide a lean carcass with little external fat, with a high yield of meat compared to more improved breeds.
Horns
Polled livestock
Polled livestock are livestock without horns, of species that normally have them. The term refers both to breeds or strains which are naturally polled through selective breeding and also to naturally horned animals which have been dehorned...
(hornless) sheep are not registrable, since this trait is considered an indication of past cross-breeding, and as such there is no such thing as a polled purebred Jacob.
The horns are normally black, but may be black and white striped; white horns are undesirable. Ideally, horns are smooth and balanced, strongly attached to the skull, and grow in a way that does not impede the animal's sight or grazing
Grazing
Grazing generally describes a type of feeding, in which a herbivore feeds on plants , and also on other multicellular autotrophs...
abilities. Rams have larger horns than ewes. The horns in two-horned sheep, and the lower horns in four-horned animals, grow in a spiral shape. The rostral set of horns usually extend upwards and outwards, while the caudal set of horns curls downwards along the side of the head and neck. On polycerate animals it is preferred that there is a fleshy gap between the two pairs of horns. Partial or deformed horns that are not firmly attached to the skull, often referred to as "scurs", are not unusual but are considered undesirable.
The multihorned trait is genetically linked
Genetic linkage
Genetic linkage is the tendency of certain loci or alleles to be inherited together. Genetic loci that are physically close to one another on the same chromosome tend to stay together during meiosis, and are thus genetically linked.-Background:...
to a condition known as split eyelid. In mild cases the eyelid shows a "peak" but does not impair vision or cause discomfort. Extreme cases (Grade 3 or higher) result in a complete separation of the upper eyelid in the middle, and these sheep should not be used for breeding.
Markings
Each Jacob has distinctive markings that enable the shepherd to identify specific sheep from a distance. Desirable color traits include an animal which is approximately 60% white, with the remaining 40% consisting of a random pattern of black or "lilac" (brownish-gray) spots or patches. The skin beneath the white fleece is pink, while skin beneath colored spots is darkly pigmented. Both rams and ewes exhibit black markings, some of which are breed specific and some of which are random.Breed specific markings include large, symmetrical dark patches incorporating the ears, eyes and cheeks, and a dark cape
Cape
Cape can be used to describe any sleeveless outer garment, such as a poncho, but usually it is a long garment that covers only the back half of the wearer, fastening around the neck. They were common in medieval Europe, especially when combined with a hood in the chaperon, and have had periodic...
over the dorsal part of the neck and shoulders. The face should have a white blaze extending from the poll to the muzzle
Snout
The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.-Terminology:The term "muzzle", used as a noun, can be ambiguous...
. The muzzle itself should be dark. The classic Jacob face is often referred to as "badger-faced", consisting of black cheeks and muzzle with a white blaze running down the front of the face. In addition to these markings, random spots may occur on the rest of the body and legs (including the carpi
Knee
The knee joint joins the thigh with the leg and consists of two articulations: one between the fibula and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus , which permits flexion and extension as...
, hocks, and pastern
Pastern
The pastern is a part of the leg of a horse between the fetlock and the top of the hoof. It incorporates the long pastern bone and the short pastern bone , which are held together by two sets of paired ligaments to form the pastern joint...
s). Certain markings are common in particular lines: large muzzle markings, lack of leg markings, lack of muzzle markings, etc.
Wool and hides
Spinning count
Spinning count is a measure of fibre fineness and distribution developed by the English. It is defined as the number of hanks of yarn that can be spun from a pound of wool. A hank of wool is 560 yards long...
(S number
S number (wool)
An S number on the label of a wool suit, or other tailored wool apparel, indicates the fineness of the wool fiber used in the making of the apparel. The numbers may also be found on wool fabric and yarn. The S numbers for fine wool products are intended to state, with precision, the fineness of the...
or Bradford count
Bradford system
The Bradford system is a way to assess the quality of wool....
) of 46–54, which corresponds to an average fiber diameter of about 32.7–27.9 micrometers
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
, or Low 1/4 Blood–1/4 Blood on the American or Blood grading system. Lambs of the more primitive lines are born with a coat of guard hair that is protective against rain and cold; this birth coat is shed at 3–6 months.
In general, the fleece is light, soft, springy and open, with little lanolin
Lanolin
Lanolin , also called Adeps Lanae, wool wax or wool grease, is a yellow waxy substance secreted by the sebaceous glands of wool-bearing animals. Most lanolin used by humans comes from domestic sheep...
(grease). The fleece generally weighs 3 to 6 lb (1.4 to 2.7 kg) and varies in crimp and fineness. Staple length is generally 3 to 5 in (7.6 to 12.7 cm) and may be up to 7 inches (17.8 cm). Similar to other unimproved breeds, most Jacobs have some white, kinky, kemp
Kemp (wool)
Kemp is generally a chalky-white, brittle, weak fibre which may be mixed with normal fibers in a sheep's wool fleece. Kemp fibres are often detached from the skin. This hair is not desirable in a fleece, as it does not accept dye, minimising both the quality and the value of the wool....
(coarse wool) in their fleece, though excessive kemp is undesirable. In some sheep (particularly British Jacobs, which have denser fleeces), the black wool will grow longer or shorter than the white wool. This is called "quilted fleece" and is an undesirable trait.
Jacobs are shorn
Sheep shearing
Sheep shearing, shearing or clipping is the process by which the woollen fleece of a sheep is cut off. The person who removes the sheep's wool is called a shearer. Typically each adult sheep is shorn once each year...
once a year, most often in the springtime
Spring (season)
Spring is one of the four temperate seasons, the transition period between winter and summer. Spring and "springtime" refer to the season, and broadly to ideas of rebirth, renewal and regrowth. The specific definition of the exact timing of "spring" varies according to local climate, cultures and...
. Some individual sheep may develop a natural "break," or marked thinning, of the fleece in springtime, which can lead to a natural shedding of the fleece, particularly around the neck and shoulders. The medium-fine grade wool has a high luster, and is highly sought after by handspinners if it is free of kemp. The colors may be separated or blended after shearing and before spinning to produce various shades of yarn from a single fleece, from nearly white to nearly black. Tanned pelts also command high market prices.
Husbandry
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
characteristics of its Old World ancestors while its British counterpart has lost many of its unimproved physical characteristics through cross-breeding and selective breeding. The British Jacob has thus diverged
Genetic divergence
Genetic divergence is the process in which two or more populations of an ancestral species accumulate independent genetic changes through time, often after the populations have become reproductively isolated for some period of time...
from the American Jacob as a result of artificial selection.
Jacobs are typically hardy, low-maintenance animals with a naturally high resistance to parasites
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
and hoof problems. Jacobs do not show much flocking behavior
Flocking (behavior)
Flocking behavior is the behavior exhibited when a group of birds, called a flock, are foraging or in flight. There are parallels with the shoaling behavior of fish, the swarming behavior of insects, and herd behavior of land animals....
. They can be skittish
Anxiety
Anxiety is a psychological and physiological state characterized by somatic, emotional, cognitive, and behavioral components. The root meaning of the word anxiety is 'to vex or trouble'; in either presence or absence of psychological stress, anxiety can create feelings of fear, worry, uneasiness,...
if not used to people, although with daily handling they will become tame
Domestication
Domestication or taming is the process whereby a population of animals or plants, through a process of selection, becomes accustomed to human provision and control. In the Convention on Biological Diversity a domesticated species is defined as a 'species in which the evolutionary process has been...
and make good pet
Pet
A pet is a household animal kept for companionship and a person's enjoyment, as opposed to wild animals or to livestock, laboratory animals, working animals or sport animals, which are kept for economic or productive reasons. The most popular pets are noted for their loyal or playful...
s. They require shelter from extreme temperatures, but the shelter can be open and simple. They tend to thrive in extremes of heat and cold and have good or excellent foraging
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
capabilities. They can secure adequate nutrition with minimal to no supplementation, even in the presence of suboptimal soil conditions.
Due to their low tail dock and generally unimproved anatomy, Jacob ewes are widely reputed to be easy-lambing. Jacobs are seasonal breeder
Seasonal breeder
Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the births at a time optimal for the survival of the young in terms of factors such as temperature, food and water. Related sexual interest and behaviors are expressed...
s, with ewes generally cycling in the cooler months of the fall. They will begin to cycle during the first fall following their birth and most often the ewe's first lamb is a single. Subsequent gestations
Pregnancy (mammals)
In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from implantation in the uterus through gestation. It begins when a fertilized zygote implants in the female's uterus; and ends once it leaves the uterus.-Fertilization and implantation:A...
will typically bear one or two lambs in the spring, and triplets are not unusual. The lambs will exhibit their spotting and horn characteristics at birth, with the horn buds more readily apparent on ram lambs. Lambs may be weaned at two months of age, but many shepherds do not separate lambs and allow the ewe to wean the lamb at about 4 months of age. Jacob ewes are instinctively attentive mothers and are protective of their lambs. They are included in commercial flocks in England because of their ease of lambing and strong mothering instincts.
Tay–Sachs disease
Tay–Sachs disease is one of several related genetic disorderGenetic disorder
A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....
s in humans known as lysosomal storage disease
Lysosomal storage disease
Lysosomal storage diseases are a group of approximately 50 rare inherited metabolic disorders that result from defects in lysosomal function...
s. It is caused by a deficiency of hexosaminidase A
Hexosaminidase
Hexosaminidase is an enzyme involved in the hydrolysis of terminal N-acetyl-D-hexosamine residues in N-acetyl-β-D-hexosaminides.- Lysosomal A, B, and S isozymes :Functional lysosomal β-hexosaminidase enzymes are dimeric in structure...
, an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
involved in the hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of GM2 ganglioside
GM2 (ganglioside)
GM2 is a type of ganglioside. It is associated with GM2 gangliosidoses such as Tay-Sachs disease....
. This enzyme deficiency is caused by a mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
on the HEXA
HEXA
Hexosaminidase A , also known as HEXA, is an enzyme that in humans is encoded by the HEXA gene.Hexosaminidase A and the cofactor GM2 activator protein catalyze the degradation of the GM2 gangliosides and other molecules containing terminal N-acetyl hexosamines...
gene on chromosome 15
Chromosome 15 (human)
right|frame|Human chromosome 15Chromosome 15 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 15 spans about 106 million base pairs and represents between 3% and 3.5% of the total DNA in cells.Identifying genes on each chromosome is an...
. An autosomal
Autosome
An autosome is a chromosome that is not a sex chromosome, or allosome; that is to say, there is an equal number of copies of the chromosome in males and females. For example, in humans, there are 22 pairs of autosomes. In addition to autosomes, there are sex chromosomes, to be specific: X and Y...
recessive disease, Tay–Sachs is characterized by progressive deterioration of mental and physical abilities
Neurodegeneration
Neurodegeneration is the umbrella term for the progressive loss of structure or function of neurons, including death of neurons. Many neurodegenerative diseases including Parkinson’s, Alzheimer’s, and Huntington’s occur as a result of neurodegenerative processes. As research progresses, many...
, usually resulting in death by the age of four years.
Recent research has revealed that this disease exists in some flocks of Jacob sheep. Four Jacob lambs from St. Jude's Farm in Lucas, Texas
Lucas, Texas
Block quoteLucas is a city in Collin County, Texas, United States. The population was 2,890 at the 2000 census. Recent population statistics show Lucas to have a population above 5,000 people ; however, the current population signs within the city limits state a population of 5015.-Geography:Lucas...
were examined for an unusual, progressive and ultimately fatal neurologic disease. Clinical findings included ataxia
Ataxia
Ataxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...
in all 4 limbs, proprioceptive
Proprioception
Proprioception , from Latin proprius, meaning "one's own" and perception, is the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement...
deficits, and cortical blindness
Cortical blindness
Cortical blindness is the total or partial loss of vision in a normal-appearing eye caused by damage to the visual area in the brain's occipital cortex. This damage is most often caused by loss of blood flow to the occipital cortex from either unilateral or bilateral posterior cerebral artery...
. The diagnosis of GM2 gangliosidosis
GM2 gangliosidoses
The GM2 gangliosidoses are a group of related genetic disorders that result from a deficiency of the enzyme beta-hexosaminidase. This enzyme catalyzes the biodegradation of fatty acid derivatives known as gangliosides. The diseases are better known by their individual names.Beta-hexosaminidase is a...
was confirmed by biochemical
Biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
and molecular genetic
Molecular genetics
Molecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics and molecular biology...
studies. Furthermore, the biochemical mechanism for this disease in the Jacob (diminished activity of hexosaminidase A resulting in increased concentrations of GM2 ganglioside) is virtually identical to that observed in humans. Sequencing
DNA sequencing
DNA sequencing includes several methods and technologies that are used for determining the order of the nucleotide bases—adenine, guanine, cytosine, and thymine—in a molecule of DNA....
of the cDNA
Complementary DNA
In genetics, complementary DNA is DNA synthesized from a messenger RNA template in a reaction catalyzed by the enzyme reverse transcriptase and the enzyme DNA polymerase. cDNA is often used to clone eukaryotic genes in prokaryotes...
of the HEXA gene of affected Jacobs reveals an identical number of nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
s and exon
Exon
An exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule either after portions of a precursor RNA have been removed by cis-splicing or when two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA...
s as in the human HEXA gene, and 86% identity in nucleotide sequence. A missense mutation
Missense mutation
In genetics, a missense mutation is a point mutation in which a single nucleotide is changed, resulting in a codon that codes for a different amino acid . This can render the resulting protein nonfunctional...
(now referred to as the G444R mutation) was found in the HEXA cDNA of the affected sheep caused by a single nucleotide change at the end of exon 11, resulting in the skipping of exon 11. This model of Tay–Sachs disease provided by the Jacob is the first to offer promise as a means for trials of gene therapy
Gene therapy
Gene therapy is the insertion, alteration, or removal of genes within an individual's cells and biological tissues to treat disease. It is a technique for correcting defective genes that are responsible for disease development...
, which may eventually prove to be useful in the treatment of the disease in humans.
Bai Zeng and Paola Torres of the Department of Neurology at New York University School of Medicine
New York University School of Medicine
The New York University School of Medicine is one of the graduate schools of New York University. Founded in 1841 as the University Medical College, the NYU School of Medicine is one of the foremost medical schools in the United States....
examined DNA samples of 443 Jacobs from various flocks within the United States. 51 of these specimens were identified as carriers
Genetic carrier
A genetic carrier , is a person or other organism that has inherited a genetic trait or mutation, but who does not display that trait or show symptoms of the disease. They are, however, able to pass the gene onto their offspring, who may then express the gene...
of the G444R mutation (a carrier incidence of 11%); 90% of the flocks were found to have one or more mutation carriers. Either Jacob parent can carry the mutant autosomal recessive gene. Carriers appear normal and live a normal life. Turner 183K, a bloodline foundation
Preservation breeding
Preservation breeding is an attempt by many animal breeders to preserve bloodlines of animals, either of a rare breed, or of rare pedigrees within a breed. One purpose of preservation breeding is to protect genetic diversity within a species, another is to preserve valuable genetic traits that may...
ram and the apparent source of the mutation in North America, was born of imported Jacobs. The primary suspect is Turner’s mother. The identification of this type of genetic defect in a foundation ram is particularly concerning because in North America, the Jacob is considered to be a bottleneck breed
Population bottleneck
A population bottleneck is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing....
representing a very small gene pool
Gene pool
In population genetics, a gene pool is the complete set of unique alleles in a species or population.- Description :A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection...
.