Dogs in Miami

The Labrador Retriever


Description

There are two types of Labradors, the English Labrador and the American Labrador. As with some other breeds, the Conformation (typically "English", "show" or "bench") and the Field (typically "American" or "working") lines differ, although both lines are bred in both countries. In general, however, Conformation Labradors tend to be bred as medium-sized dogs, shorter and stockier with fuller faces and a slightly calmer nature than their Field counterparts, which are often bred as taller, lighter-framed dogs, with slightly less broad faces and a slightly longer nose; however Field Labradors should still be proportional and fit within AKC standards. With field Labradors, excessively long noses, thin heads, long legs and lanky frames are not considered standard. These two types are informal and not codified or standardized; no distinction is made by the AKC or other kennel clubs, but the two types come from different breeding lines. Australian stock also exists; though not seen in the west, they are common in Asia.

Labradors are relatively large, with males typically weighing 29 to 41 kg (64 to 90 lb) and females 25 to 32 kg (55 to 71 lb). Labradors weighing close to or over 100 lb (45 kg) are considered obese or having a major fault under American Kennel Club standards, although some Labradors weigh significantly more. They can vary in height typically the Dogs 22-24 inches (56-61cm.) and the Bitches 21-23 inches (53-58cm.) The English bred lab comes from English bred stock. Their general appearance is different. The English bred labs are heavier, thicker and blockier. The American bred Lab comes from American bred stock and is tall and lanky. The majority of the characteristics of this breed, with the exception of color, are the result of breeding to produce a working retriever.

The Labrador has a double coat, The double coat is smooth and does not have any waves. Coat colors come in solid black, yellow, or chocolate. There is also said to be a rare silver or gray color that is referred to by the AKC as a shade of chocolate. This color is controversial and some claim it is a Weimaraner cross, while others say it is a true mutation. The breed tends to shed hair twice annually, or regularly throughout the year in temperate climates. Some Labradors shed considerably; however, individual Labradors vary. Labrador hair is usually fairly short and straight, and the tail quite broad and strong. The head of the Labrador is broad with a moderate stop.

The nose is thick, black on black and yellow dogs and brown on chocolate dogs. The nose color often fades and is not considered a fault in the show ring. The teeth should meet in a scissors or level bite. The muzzle is fairly wide. The neck is proportionately wide and powerful. The body is slightly longer than tall. The short, hard coat is easy to care for and water-resistant. The medium sized eyes are set well apart. Eye color should be brown in yellow and black dogs and hazel or brown in chocolate dogs. Some labs can also have green or greenish yellow eyes. In silver dogs the eye color is usually gray. The eye rims are black in yellow and black dogs and brown in chocolate dogs. The ears are medium in size, hanging down and pendant in shape. The otter tail is thick at the base, gradually tapering towards the tip. It is completely covered with short hair, with no feathering. The otter-like tail and webbed toes of the Labrador Retriever make them excellent swimmers. The webbing between their toes can also serve as a "snowshoe" in colder climates and keep snow from balling up between their toes- a condition that can be painful to other breeds with hair between the toes. Their interwoven coat is also relatively waterproof, providing more assistance for swimming.

History

Once known as the "St John's Dogs," the Labrador retriever is one of the most popular breeds in the United States. The Lab is native to Newfoundland, The St. John's area of Newfoundland was settled mainly by the English and Irish. Local fishermen originally used the St. John's dog to assist in carrying ropes between boats, towing dories, and helping to retrieve fishnets in the water. The Labrador's loyalty and hard working behavior were valuable assets for fishermen.

The modern Labrador's ancestors originated on the island of Newfoundland, now part of the province of Newfoundland and Labrador, Canada. The founding breed of the Labrador was the St. Johns water dog, (also a founding breed of the Newfoundland), a breed that emerged through ad-hoc breeding by early settlers of the island in the 16th century. The forebears of the St. John's Dog are not known, but were likely a random-bred mix of English, Irish, and Portuguese working breeds. The Newfoundland (known then as the Greater Newfoundland) is likely a result of the St. John's Dog breeding with mastiffs brought to the island by the generations of Portuguese fishermen who had been fishing offshore since the 16th century. The smaller short-coated St. John's Dog (also known then as the Lesser Newfoundland) was used for retrieval and pulling in nets from the water. These smaller dogs were the forebears of the Labrador Retriever. The white chest, feet, chin, and muzzle - known as tuxedo markings - characteristic of the St. John's Dog often appear in modern Lab mixes, and will occasionally manifest in Labradors as a small white spot on the chest (known as a medallion) or stray white hairs on the feet or muzzle.

A number of St. John's Dogs were brought back to the Poole area of England in the early 19th century, then the hub of the Newfoundland fishing trade, by the gentry, and became prized as sporting and waterfowl hunting dogs A few kennels breeding these grew up in England; at the same time a combination of sheep protection policy (Newfoundland) and rabies quarantine (England) led to their gradual demise in their country of origin.

A surviving picture of Buccleuch Avon (b.1885), a foundational dog of many modern Labrador lineages.The first and second Earls of Malmesbury, who bred for duck shooting on his estate, and the 5th and 6th Dukes of Buccleuch, and youngest son Lord George William Montagu-Douglas-Scott, were instrumental in developing and establishing the modern Labrador breed in 19th century England. The dogs Avon ("Buccleuch Avon") and Ned given by Malmesbury to assist the Duke of Buccleuch's breeding program in the 1880s are considered the ancestors of all modern Labradors The first St. John's dog was said to be brought to England around 1820; however, the breed's reputation had spread to England long before. There is a story that the Earl of Malmesbury saw a St. John's Dog on a fishing boat and immediately made arrangements with traders to have some of these dogs exported to England. These ancestors of the first labradors so impressed the Earl with their skill and ability for retrieving anything within the water and on shore that he devoted his entire kennel to developing and stabilising the breed.

Early descriptions

Several early descriptions of the St. John's Water Dog exist. In 1822, explorer W.E. Cormack crossed the island of Newfoundland by foot. In his journal he wrote "The dogs are admirably trained as retrievers in fowling, and are otherwise useful.....The smooth or short haired dog is preferred because in frosty weather the long haired kind become encumbered with ice on coming out of the water."

Another early report by a Colonel Hawker described the dog as "by far the best for any kind of shooting. He is generally black and no bigger than a Pointer, very fine in legs, with short, smooth hair and does not carry his tail so much curled as the other; is extremely quick, running, swimming and fighting....and their sense of smell is hardly to be credited...."

In his book Excursions In and About Newfoundland During the Years 1839 and 1840, the geologist Joseph Beete Jukes describes the St. John's Water Dog. "A thin, short-haired, black dog came off-shore to us to-day. The animal was of a breed very different from what we understand by the term Newfoundland dog in England. He had a thin, tapering snout, a long thin tail, and rather thin, but powerful legs, with a lank body, – the hair short and smooth." wrote Jukes. "These are the most abundant dogs in the country...They are no means handsome, but are generally more intelligent and useful than the others...I observed he once or twice put his foot in the water and paddled it about. This foot was white, and Harvey said he did it to "toil" or entice the fish. The whole proceeding struck me as remarkable, more especially as they said he had never been taught anything of the kind."

Name

The foundational breed of what is now the Labrador Retriever was known as the St. John's Water Dog, St. John's Dog, or Lesser Newfoundland. When the dogs were later brought to England, they were named after the geographic area known as "the Labrador" or simply Labrador to distinguish them from the larger Newfoundland breed, even though the breed was from the more southern Avalon Peninsula.

Official breed standards

There is a great deal of variety among Labradors. The following characteristics are typical of the conformation show bred (bench-bred) lines of this breed in the United States, and are based on the AKC standard. Significant differences between UK and US standards are noted.

  • Size: Labradors are a medium-large but compact breed. They should have an appearance of proportionality. They should be as long from the withers to the base of the tail as they are from the floor to the withers. Males should stand 22.5 to 24.5 inches tall at the withers and weigh 65 to 80 lb. Females should stand 21.5 to 23.5 inches and weigh 55 to 70 lb. By comparison under UK Kennel Club standards, height should be 22 to 22.5 inches for males, and 21.5 to 22 inches for females. length from the point of the shoulder to the point of the rump is equal to or slightly longer than the distance from the withers to the ground. Distance from the elbow to the ground should be equal to one half of the height at the withers. The body must be of sufficient length to permit a straight, free and efficient stride; but the dog should never appear low and long or tall and leggy in outline.
  • Coat: The coat is a distinctive feature of the Labrador Retriever. The Lab's coat should be short and dense, but not wiry. The coat is described as 'water-resistant' or more accurately 'water-repellent' so that the dog does not get cold when taking to water in the winter. That means that the dog naturally has a slightly dry, oily coat. Acceptable colors are black, yellow (ranging from ivory or crème to fox red), and chocolate.
  • Head: The skull should be wide; well developed but without exaggeration. The head should be broad with a pronounced stop and slightly pronounced brow. The eyes should be kind and expressive. Appropriate eye colors are brown and hazel. The lining around the eyes should be black. The ears should hang close to the head and are set slightly above the eyes. Ears should not be large and heavy, but in proportion with the skull and reach to the inside of the eye when pulled forward
  • Jaws: The jaws should be strong and powerful. The muzzle should be of medium length, and should not be too tapered. The jaws should hang slightly and curve gracefully back. The teeth should be strong and regular with a scissors bite; the lower teeth just behind, but touching the inner side of the upper incisors
  • Body: The body should be strong and muscular with a level top line. Forequarters should be muscular, well coordinated and balanced with the hindquarters. The Labrador’s hindquarters are broad, muscular and well-developed from the hip to the hock with well-turned stifles and strong short hocks. Viewed from the rear, the hind legs are straight and parallel.

The tail and coat are designated "distinctive [or distinguishing] features" of the Labrador by both the Kennel Club and AKC. The AKC adds that "true Labrador Retriever temperament is as much a hallmark of the breed as the 'otter' tail."

Color

Different shades of yellow: a usual yellow shade, and a fox red shade. The three primary color varieties of the Labrador Retriever Labrador Retrievers are registered in three colors: black (a solid black color), yellow (anything from light cream to "fox-red"), and chocolate (medium to dark brown). Some Labrador retrievers can have markings such as white patches on their chest and other areas, but most commonly they are one solid color.

Puppies of all colors can potentially occur in the same litter. Color is determined primarily by two genes. The first gene (the B locus) determines the density of the coat's pigment granules: dense granules result in a black coat, sparse ones give a chocolate coat. The second (D) locus determines whether the pigment is produced at all. A dog with the recessive d allele will produce little pigment and will be yellow regardless of its genotype at the B locus. Variations in numerous other genes control the subtler details of the coat's coloration, which in yellow Labradors varies from white to light gold to a fox red. Chocolate and black Labradors' noses will match the coat color.

Nose and skin pigmentation

Because Labrador colouration is controlled by multiple genes, it is possible for recessive genes to emerge some generations later and also there can sometimes be unexpected pigmentation effects to different parts of the body. Pigmentation effects appear in regard to yellow Labradors, and sometimes chocolate, and hence the majority of this section covers pigmentation within the yellow Labrador. The most common places where pigmentation is visible are the nose, lips, gums, feet, tail, and the rims of the eyes, which may be black, brown, light yellow-brown ("liver", caused by having two genes for chocolate), or several other colours. A Labrador can carry genes for a different color, for example a black Labrador can carry recessive chocolate and yellow genes, and a yellow Labrador can carry recessive genes for the other two colors. DNA testing can reveal some aspects of these. Less common pigmentations (other than pink) are a fault, not a disqualification, and hence such dogs are still permitted to be shown. The intensity of black pigment on yellow Labradors is controlled by a separate gene independent of the fur coloring. Yellow Labradors usually have black noses, which may gradually turn pink with age (called "snow nose" or "winter nose"). This is due to a reduction in the enzyme tyrosinase which indirectly controls the production of melanin, a dark coloring. Tyrosinase is temperature dependent—hence light colouration can be seasonal, due to cold weather—and is less produced with increasing age two years old onwards. As a result, the nose color of most yellow Labradors becomes a somewhat pink shade as they grow older.[

A seven-week old Dudley Lab. The nose and lips are pink or flesh-colored, the defining aspect of Dudley pigmentation.

A colouration known as "Dudley" is also possible. Dudleys are variously defined as yellow Labradors which have unpigmented (pink) noses (LRC), yellow with liver/chocolate pigmentation (AKC), or "flesh coloured" in addition to having the same colour around the rims of the eye, rather than having black or dark brown pigmentation. A yellow Labrador with brown or chocolate pigmentation, for example, a brown or chocolate nose, is not necessarily a Dudley, though according to the AKC's current standard it would be if it has chocolate rims around the eyes (or more accurately of the genotype eebb). Breed standards for Labradors considers a true Dudley to be a disqualifying feature in a conformation show Lab, such as one with a thoroughly pink nose or one lacking in any pigment along with flesh coloured rims around the eyes. True Dudleys are extremely rare.

Breeding in order to correct pigmentation often lacks dependability. Because colour is determined by many genes, some of which are recessive, crossbreeding a pigmentation non-standard yellow Labrador to a black Labrador may not correct the matter or prevent future generations carrying the same recessive genes. For similar reasons, crossbreeding chocolate to yellow Labradors is also often avoided.

Show and field lines

Chocolate Labradors from field-bred stock are typically lighter in build and have a shorter coat than conformation show Labrador.

There are significant differences between field and trial-bred (sometimes referred to as "American") and show-bred (or "English") lines of Labradors, arising as a result of specialised breeding. Dogs bred for hunting and field-trial work are selected first for working ability, where dogs bred to compete in conformation shows are selected for their conformation to the standards and characteristics sought by judges in the show ring.

Head and muzzle appearance: American or field (left), and English or show (right), showing the shorter muzzle length, more solid appearance head, and "pronounced" stop of the latter.

While individual dogs may vary, in general show-bred Labradors are heavier built, slightly shorter-bodied, and have a thicker coat and tail. Field Labradors are generally longer legged, lighter, and more lithe in build. In the head, show Labradors tend to have broader heads, better defined stops, and more powerful necks, while field Labradors have lighter and slightly narrower heads with longer muzzles. Field-bred Labradors are commonly higher energy and more high-strung compared to the Labrador bred for conformation showing, and as a consequence may be more suited to working relationships than being a "family pet". Some breeders, especially those specializing in the field type, feel that breed shows do not adequately recognize their type of dog, leading to occasional debate regarding officially splitting the breed into subtypes.

In the United States, the AKC and the Labrador's breed club have set the breed standard to accommodate the field-bred Labrador somewhat. For instance, the AKC withers-height standards allow conformation dogs to be slightly taller than the equivalent British standard. However, dual champions, or dogs that excel in both the field and the show ring, are becoming more unusual.

Temperament

One of the most popular breeds in the USA, the Labrador Retriever is loyal, loving, affectionate and patient, making great family dogs. Labradors' sense of smell is so keen it allows them to hone in on almost any scent and follow the path of its origin. They generally stay on the scent until they find it. They love to play, especially in water, never wanting to pass up the opportunity for a good swim. These lively dogs have an excellent, reliable, temperament and are friendly, superb with children and equable with other dogs. Labradors instinctively enjoy holding objects and even hands or arms in their mouths, which they can do with great gentleness (a Labrador can carry an egg in its mouth without breaking it). They are also known to have a very soft feel to the mouth, as a result of being bred to retrieve game such as waterfowl. These dogs are watchdogs, not guard dogs, although some have been known to guard. They can become destructive if the humans are not 100% pack leader and/or if they do not receive enough mental and physical exercise, and left too much to their own devices. They are prone to chewing objects (though they can be trained out of this behavior).

The Labrador Retriever's coat repels water to some extent, thus facilitating the extensive use of the dog in waterfowl hunting. Labradors have a reputation as a very even-tempered breed and an excellent family dog (including a good reputation with children of all ages and other animals), but some lines (particularly those that have continued to be bred specifically for their skills at working in the field rather than for their appearance) are particularly fast and athletic. Their fun-loving boisterousness and lack of fear may require training and firm handling at times to ensure it does not get out of hand—an uncontrolled adult can be quite problematic. Females may be slightly more independent than males. Labradors mature at around three years of age; before this time they can have a significant degree of puppy-like energy, often mislabeled as being hyperactive Because of their enthusiasm, leash-training early on is suggested to prevent pulling when full-grown. Labradors often enjoy retrieving a ball endlessly and other forms of activity (such as agility, Frisbee, or fly ball). Although they will sometimes bark at noise, especially noise from an unseen source ("alarm barking"), Labradors are usually not noisy or territorial. They are often very easygoing and trusting with strangers, and therefore are not usually suitable as guard dogs.

Labradors have a well-known reputation for appetite, and some individuals may be highly indiscriminate, eating digestible and non-food objects alike. They are persuasive and persistent in requesting food. For this reason, the Labrador owner must carefully control his/her dog's food intake to avoid obesity and its associated health problems (see below). The steady temperament of Labradors and their ability to learn make them an ideal breed for search and rescue, detection, and therapy work. Their primary working role in the field continues to be that of a hunting retriever.

Health

Labrador pups generally are not brought to the home before they are 8 weeks old. Their life expectancy is generally 10 to 12 years and it is a healthy breed with relatively few major problems. Notable issues related to health and well-being include:

Inherited disorders

  • Labradors are somewhat prone to hip and elbow dysplasia which involves abnormal development or degeneration of the joints, especially the larger dogs, though not as much as some other breeds. Hip scores are recommended before breeding and often joint supplements are recommended.
  • Lymphoma which is a cancer that affects lymph nodes and other organs containing lymphoid tissue.
  • Labradors also suffer from the risk of knee problems. A Patellar luxation also known as a slipped knee cap is a common occurrence in the knee where the leg is often bow shaped.
  • Eye problems are also possible in some Labradors, particularly progressive retinal atrophy, Entropion, Glaucoma, cataract, corneal dystrophy and retinal dysplasia. Dogs which are intended to be bred should be examined by a veterinary ophthalmologist for an eye score.
  • Hereditary myopathy, a rare inherited disorder that causes a deficiency in type II muscle fibre. Symptoms include a short stilted gait or "bunny hopping," and in rare cases ventroflexion of the neck accompanied by a kyphotic posture.
  • There is a small incidence of other conditions, such as autoimmune diseases and deafness in Labradors, either congenitally or later in life.
  • Labradors often suffer from exercise induced collapse, a syndrome that causes hyperthermia, weakness, collapse, and disorientation after short bouts of exercise.

Obesity

Labradors like to eat so, naturally, they get fat. This breed tends to gain weight quickly. Laziness also contributes to this. A healthy Labrador should keep a very slight hourglass waist and be fit and light, rather than fat or heavy-set. They need to be taken on a daily, brisk, long walk, jog or run alongside you when you bicycle. While out on the walk the dog must be made to heel beside or behind the person holding the lead, as in a dog's mind the leader leads the way, and that leader needs to be the human. When they are fat, they usually develop hip dysplasia or other joint problems and get diabetes. Osteoarthritis is common in older, especially overweight, Labradors. A 14 year study covering 48 dogs by food manufacturer Purina showed that Labradors fed to maintain a lean body shape outlived those fed freely, by around two years, emphasizing the importance of not over-feeding.

Use as working dogs

Labradors are a very popular selection for use as guide dogs. Although Labradors are tremendous pets, both loving and affectionate, they also make excellent working dogs. In the United States, there are in reality two types of the Labrador retriever, the field line and the show line. The show line is used for show ring functions and is bred for compliance and temperament. Needless to say, the Labrador stands out in both these fields, and many owners have had the satisfaction of seeing their dog win a prize at one of these events. However, The field line is bred for the purpose of field and hunting ability. The main difference between the two lines is that Labradors in the field line will display a little more drive and energy, though the show line has a great deal of energy as well.

Labradors are an intelligent breed with a good work ethic and generally good temperaments (breed statistics show that 92.3% of Labradors who were tested passed the American Temperament Test.) Common working roles for Labradors include: hunting, tracking and detection (they have a great sense of smell which helps when working in these areas), disabled-assistance, carting, and therapy work. Approximately 60–70% of all guide dogs in Canada are Labradors; other common breeds are Golden Retrievers and German Shepherd Dogs.

The high intelligence, initiative and self-direction of Labradors in working roles is exemplified by dogs such as Endal, who during a 2001 emergency placed an unconscious human being in the recover position, retrieved his mobile phone from beneath the car, fetched a blanket and covered him, barked at nearby dwellings for assistance, and then ran to a nearby hotel to obtain help. A number of Labradors have also been taught to assist their owner in removing money and credit cards from ATMs with prior training.

The breed is used in water rescue/lifesaving. It continues in that role today, along with the Leonberger, Newfoundland and Golden Retriever dogs; they are used at the Italian School of Canine Lifeguard.

Exploration

Labradors as a breed are curious, exploratory and Love Company following both people and interesting scents for food, attention and novelty value. They do not typically jump high fences or dig. Because of their personalities, some Labradors climb and/or jump for their own amusement. As a breed they are highly intelligent and capable of intense single-mindedness and focus if motivated or their interest is caught. Therefore, with the right conditions and stimuli, a bored Labrador could "turn into an escape artist par excellence".

Demography

The Labrador is an exceptionally popular dog. For example as of 2006:

  • Widely considered the most popular breed in the world.
  • Most popular dog by ownership in Australia, Canada, Israel. New Zealand UK, and USA (since 1991),
  • In both the UK and USA, there are well over twice as many Labradors registered as the next most popular breed. If the comparison is limited to dog breeds of a similar size, then there are around 3 - 5 times as many Labradors registered in both countries as the next most popular breeds, the German Shepherd and Golden Retriever.
  • Most popular breed of assistance dog in the United States, Australia and many other countries, as well as being widely used by police and other official bodies for their detection and working abilities. Approximately 60–70% of all guide dogs in the United States are Labradors (see below).
  • Seven out of 13 of the Australian National Kennel Council "Outstanding Gundogs" Hall of Fame appointees are Labradors (list covers 2000–2005).

There is no global registry of Labradors, nor detailed information on numbers of Labradors living in each country. The countries with the five largest numbers of Labrador registrations as of 2005 are: 1: United Kingdom 2: France and United States (approximately equal), 4: Sweden, 5: Finland. Sweden and Finland have far lower populations than the other three countries, suggesting that as of 2005 these two countries have the highest proportion of Labradors per million people:

Labrador hybrids

The "Labradoodle" is a trendy "designer dog" that is a cross-bred Labrador and Poodle. A concept that originated in Australia, the intent of breeding this cross was to try and create a service dog suitable for allergy sufferers. However the current fashion for Labradoodles has resulted in indiscriminate breeding, and there is no guarantee such a cross will inherit the hypo-allergenic poodle coat.

Some assistance-dog groups use Golden Retriever / Labrador Retriever hybrids (unofficially called a Golden Labrador Retriever) because they believe this cross produces dogs with excellent temperaments. However, such crossbreeds are not immune to many of the problems suffered by purebreds, as Golden Retrievers and Labradors have similar health problems.

There are also Mastadors, crosses between the Labrador Retriever and the Mastiff, like Spike that played Old Yeller.

There are even Labrador hybrids, named "Spanadors", crossed with Cocker Spaniels, which can reduce certain bone problems, due to their smaller bodies. They were originally bred to be designer dogs, with their coats coming in many different colors and length.

The assistance dog organisation Mira utilises Labrador-Bernese Mountain Dog crosses ("Labernese") with success.

Genotypes

In order to analyze and understand the inheritance of coat colour in Labradors, a few conventions need to be stated. First, the actual appearance of the dog (black, chocolate, or yellow) is the phenotype. There are at least nine combinations of alleles that underlie the three colours of the Labrador. These allelic combinations are called genotypes. One allele is inherited from the gametes of the sire and the other allele is inherited from the gametes of the dam. In simple Mendelian Inheritance, one allele overrides or is dominant to the other, resulting in the dominant allele being expressed in the phenotype. Recessive alleles will be expressed in the phenotype when the individual is homozygous recessive, or carries two recessive alleles. When reporting genotypes, dominant alleles are written as capital letters (B) while their recessive counterparts are written with lower case letters (b).

Carol Coode, a well-known Labrador Retriever breeder and judge from England presents the main alleles governing the inheritance of coat colour in Labrador Retrievers as:

B = black

b = chocolate

E = ability to express pigment or coat colour

e = inability to express dark pigment or coat colour

There is another C allele that works in yellow Labradors which will be discussed later. This C allele is responsible for producing red pigment.

In 1977, Templeton, Stewart, and Fletcher published their research regarding Labrador Coat colour Inheritance in The Journal of Heredity. They used a line of purebred Labrador Retrievers developed at the University of Oregon Health Sciences Center in Portland Oregon and used a series of test crosses and experimental breeding to test their hypothesis. They hypothesized that black and chocolate coat colours are determined by simple Mendelian inheritance at the B locus and that yellow coat colour is determined by a simple Mendelian inheritance at the E locus, which is separate from the B locus. They found that black (B) coat colour is dominant to chocolate (b) coat colour and yellow coat colour allele e is recessive to E and is epistatic to the B locus. The B locus is responsible for pigmentation of eyes, lips, nose, and eye rims of yellow dogs.

The following are the possible genotypes for a given Labrador as presented by Carol Coode(1993):

  • Labradors whose phenotype is Black, can have the genotypes: BBEE, BBEe, BbEE, or BbEe.

Black Labradors must have at least one dominant B allele that codes for black pigment and one dominant E allele which codes for the expression of pigment or coat colour.

  • Labradors whose phenotype is Chocolate, can have the genotypes: bbEE and bbEe.

Chocolate Labradors must be homozygous recessive for the B allele (bb) and have at least 1 domnant E allele to code for expression.

  • Labradors whose phenotype is Yellow with normal, black pigment, can have the genotypes Bbee or BBee.

In order for the desirable, dark pigment to be expressed, a yellow dog must have a dominant B allele. Yellow dogs result from being homozygous recessive for the E allele (ee) which masks expression of coat colour pigment. The presence of two recessive E alleles always masks the effects of the B alleles no matter what type of B allele (domiant or recessive) is present.

  • Labradors whose phenotype is Yellow with pale pigment or chocolate pigment or an absence of pigment, will have the genotype bbee.

Because this dog is homozygous recessive for the E allele (ee), he cannot express dark pigment. This, combined with the double chocolate gene (bb), results in the yellow dog having very pale skin pigment (lips, nose, eye-rims, etc.) usually seen in chocolate labradors. These dogs are often referred to as Dudleys; they are considered to be a disqualification under current standards.

The outcomes of any cross can be determined with a simple Punnett Square for 2 alleles. For example, a Black dog, with the genotype B/B;E/E bred to any other genotype will produce all Black puppies because the dominant black dog will always produce gametes with B and E. Anytime B and E are paired, no matter what the other allele is, the result will be a black dog. This phenomenon is referred to as recessive epistasis.This is due to the fact that the recessive allele e is epistatic to the ability to express pigment or coat colour.

Biochemical pathway

Melanin

The pigmentation of Labradors is controlled by melanin, a pigment molecule. Melanin is controlled by the “B” locus and when its gene product is made, it is packaged into melanosomes, small organelles in each cell. Melanosomes are transferred by melanocytes into the cells that make up the structure for the eyes, hair, and skin. The colour of the cells is determined by the colour of the melanosome and the density of melanosomes within the cell. (Davol, 1999)

In coat colour of dogs, there are two types of melanin: eumelanin and pheomelanin. Eumelanin is responsible for black or brown pigment and pheomelanin is responsible for red or yellow pigment.

Eumelanin, controlled by the B locus, is responsible for producing and packaging the melanin into the melanosome. Both the “B” and “b” alleles will produce eumelanin that contribute to pigmentation, but the dominant allele “B” is more efficient and packs more melanin into each melanosome, producing a black dog. The less efficient recessive allele “b” is responsible for chocolate colouration when the individual is homozygous recessive at the B locus. (Davol, 1999 and Hales, 2007)

Pheomelanin, controlled by the C locus, is responsible for the red/yellow pigment and is always produced, whether or not eumelanin (black/brown) is produced. When the eumelanin is not produced, due to epistasis, the pheomelanin is the only pigment in the cell, resulting in a yellow coated Labrador. A yellow dog can have any of these genotypes at the “C” locus: C/C, C/c, or c/c. The C/C produces more pigment, resulting in a darker yellow and the c/c genotype results in a lighter yellow dog. An individual heterozygous for the “C” allele (C/c) will be a medium shade of yellow. (Davol, 1999 and Hales, 2007).

Epistasis

Epistasis, as defined by iGenetics: a Molecular Approach, “is the interaction between two or more genes that controls a single phenotype. For instance, the expression of a gene at one locus can mask or suppress the expression of a gene at another locus.” (733). Labrador coat colour inheritance, the E (expression allele) masking B (pigment allele) is an example of recessive epistasis, where an individual homozygous for E (ee) masks the pigment coded for by the B allele, resulting in a yellow dog, despite the genotype at the B locus (BB, Bb, or bb). The homozygous e allele does not completely restrict the expression of the B locus alleles as they are responsible for the pigmentation of the iris, lips, nose, and eye rims of a yellow dog (Templeton 1997).

Role of the E locus

In Labradors, melanin will only be made if the cell receives a signal to do so, this signal is coded for by the E Locus, which codes for the melanocyte stimulating hormone receptor (MC1R). Labradors that are homozygous dominant for the E allele (E/E) have a mutant, extremely active form of MC1R where eumelanin is constantly being produced, so the dog will appear either black or chocolate. Labradors that are homozygous recessive for the E allele (e/e) also have a mutant for of MC1R, but this mutant is a “loss of function” receptor that cannot produce eumelanin. Labradors that are homozygous recessive for the E allele will only produce pheomelanin and will appear yellow. The recessive E allele (e/e) masks the B allele which is an example of recessive epistasis. This means that if the genotype for an individual is homozygous recessive, it will not matter what the B locus allele is for coat colour, all individuals will be yellow because the black/brown pigment will not be produced. The E allele masks the dominant C allele (red/yellow pigment) and is an example of dominant epistasis. This means that if there is a single dominant E allele, either black or brown pigment will be produced and the red/yellow pigment coded for by the C allele will not be visible. (Davol 1999).

It is interesting to note that in 2000, Everts et al. isolated and cloned the gene responsible for the MC1R receptor in dogs. The yellow Labrador has a substitution in this gene which changes the codon for Arginine to a stop codon. This nonsense mutation is found in yellow Labradors as well as Golden retrievers. Seventeen different breeds of dogs were tested for this mutation and none had it, suggesting that this mutation leads to the yellow coat colour and that this mutation has a common origin in the two breeds.

Mosaics and other "mis-marks"

Sponenberg and Bigelow published their findings in the Journal of Heredity on a mosaic male Labrador Retriever who exhibited random, but distinct black and yellow patches throughout his coat. He was the result of a black female (carrying yellow) bred to a yellow male. This dog was mated to 2 yellow females, one black female, and 2 chocolate females. All puppies resulting from these breedings were either black or yellow and the percentages of each in each mating follow the inheritance pattern of a yellow Labrador (BBee) with black pigment. They explained that this pattern was not characteristic of a “merle” coat because merle develops from a transposable element and because all of the mosaic dog’s puppies did not exhibit mosaic colouring, but were normal black or yellow, therefore there is no evidence of a transposable element. Sponenberg acknowledges the likelihood of a recessive gene causing this mosaic pattern, but says it would be unique and is highly unlikely. The most probable cause was a somatic mutation early in development. (1987)

Other “mis-marks” such as brindling, tan points, white spots, and rings around the tails are common in Labradors. Each of these conditions have various underlying genetic as well as environmental causes. Examples of “mis-marked” Labradors can be found at.