The leopard complex is a group of genetically-related coat patterns

Equine coat color

Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them.While most horses remain the same color throughout life, a few, over the course of several years, will develop a different coat color from that with which they were born...

 in horse

Horse

The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

s. These patterns range from progressive increases in interspersed white hair similar to graying

Gray (horse)

Gray or grey is a coat color of horses characterized by progressive silvering of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike many depigmentation genes, gray does not affect skin or eye color Their adult hair coat is white, dappled, or white intermingled...

 or roan

Roan (horse)

Roan is a horse coat color pattern characterized by an even mixture of colored and white hairs on the body, while the head and "points"—lower legs, mane and tail—are more solid-colored. The roan pattern is dominantly-inherited, and is found in many horse breeds...

 to distinctive, Dalmatian

Dalmatian (dog)

The Dalmatian is a breed of dog whose roots are often said to trace back to Dalmatia, a region of Croatia where the first illustrations of the dog have been found. The Dalmatian is noted for its unique black- or brown-spotted coat and was mainly used as a carriage dog in its early days...

-like leopard

Leopard (pattern)

Leopard is a term used to describe a spotted color pattern, particularly in the hair coat or skin of animals, but also used to describe spotting patterns in plants and fabrics...

 spots on a white coat. Secondary characteristics associated with the leopard complex include a white sclera

Sclera

The sclera , also known as the white or white of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In the development of the embryo, the sclera is derived from the neural crest...

 around the eye, striped hooves

Horse hoof

A horse hoof is a structure surrounding the distal phalanx of the 3rd digit of each of the four limbs of Equus species, which is covered by complex soft tissue and keratinised structures...

 and mottled skin. The leopard complex genes are also linked to abnormalities in the eyes and vision. These patterns are most closely identified with the Appaloosa horse breed, though its presence in breeds from Asia to western Europe has indicated that it is due to a very ancient 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...

.

Leopard complex patterns

Coat patterns in the leopard complex range from being hardly distinguishable from an unaffected coat, to nearly pure white. Unlike most other spotting patterns

Pinto horse

A pinto horse has a coat color that consists of large patches of white and any other color. The distinction between "pinto" and "solid" can be tenuous, as so-called "solid" horses frequently have areas of white hair. Various cultures throughout history appear to have selectively bred for pinto...

, the spotting and especially the white regions associated with the leopard complex tend to be symmetrical and originate over the hips. Furthermore, a certain amount of this inherited white patterning is present at birth. The amount of white, even if none is present at birth, often grows throughout the horse's life by gradual "roaning" which is not related to graying

Gray (horse)

Gray or grey is a coat color of horses characterized by progressive silvering of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike many depigmentation genes, gray does not affect skin or eye color Their adult hair coat is white, dappled, or white intermingled...

 or true roan

Roan (horse)

Roan is a horse coat color pattern characterized by an even mixture of colored and white hairs on the body, while the head and "points"—lower legs, mane and tail—are more solid-colored. The roan pattern is dominantly-inherited, and is found in many horse breeds...

. Colored spots reflect the underlying coat color, be it black

Black (horse)

Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and novices frequently mistake dark chestnuts or bays for black. However, some breeds of horses, such as the Friesian horse, Murgese and Ariegeois are almost exclusively black...

, chestnut

Chestnut (coat)

Chestnut is a hair coat color of horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat. Genetically and visually, chestnut is characterized by the absolute absence of true black hairs...

, gray, or silver

Silver dapple gene

The silver dapple gene is a dilution gene that affects the black base coat color. It will typically dilute a black mane and tail to flaxen, and a black body to a shade of brown or chocolate. It is responsible for a group of coat colors in horses called "silver dapple" in the west, or "taffy" in...

 dun-buckskin. A number of factors, each separately, genetically controlled, interact to produce familiar patterns such as "snowflake," "leopard," and "fewspot".

Leopard spotting

A single, incomplete dominant gene (Lp) controls the presence of leopard-spotting in horses. A dominant

Dominance relationship

Dominance in genetics is a relationship between two variant forms of a single gene, in which one allele masks the effect of the other in influencing some trait. In the simplest case, if a gene exists in two allelic forms , three combinations of alleles are possible: AA, AB, and BB...

 gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

 requires only a single copy to produce an affected phenotype

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...

; an incomplete dominant gene produces a different result depending on whether one or two copies are present. A horse's genotype may be lp/lp (homozygous

Zygosity

Zygosity refers to the similarity of alleles for a trait in an organism. If both alleles are the same, the organism is homozygous for the trait. If both alleles are different, the organism is heterozygous for that trait...

 recessive), Lp/lp (heterozygous

Zygosity

Zygosity refers to the similarity of alleles for a trait in an organism. If both alleles are the same, the organism is homozygous for the trait. If both alleles are different, the organism is heterozygous for that trait...

), or Lp/Lp (homozygous dominant). Horses without a dominant Lp gene do not exhibit leopard-complex traits, and cannot produce offspring with the Lp gene unless it is contributed by the other parent. Such horses are termed "non-characteristic" among Appaloosa horse aficionados. Horses with at least one Lp gene possess, at the very least, leopard-complex "characteristics":

• skin
  Skin
  -Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
  
   that is mottled, speckled or blotchy around the muzzle, eyes, genitals, and anus; the remainder of the body may be primarily pigmented (gray or black in the absence of other genes), primarily unpigmented (pink or flesh-colored), or mottled,
• striped hooves
  Horse hoof
  A horse hoof is a structure surrounding the distal phalanx of the 3rd digit of each of the four limbs of Equus species, which is covered by complex soft tissue and keratinised structures...
  
  ,
• white sclera
  Sclera
  The sclera , also known as the white or white of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In the development of the embryo, the sclera is derived from the neural crest...
  
  .

The presence of regions of alternating pigmented and unpigmented skin may not definitively suggest the leopard gene. They may not be visible due to the effects of other genes. For example, extensive white markings on the face may mask the presence of mottling around the eyes and muzzle, and white markings on the legs often end in white hooves. Furthermore, other genes may produce similar conditions: white sclera are associated with broad white face markings

Horse markings

Markings on horses usually are distinctive white areas on an otherwise dark base coat color. Most horses have some markings, and they help to identify the horse as a unique individual. Markings are present at birth and do not change over the course of the horse's life...

, striped hooves with the Silver dapple gene

Silver dapple gene

The silver dapple gene is a dilution gene that affects the black base coat color. It will typically dilute a black mane and tail to flaxen, and a black body to a shade of brown or chocolate. It is responsible for a group of coat colors in horses called "silver dapple" in the west, or "taffy" in...

, and freckled skin with the Champagne gene

Champagne gene

The champagne gene is a simple dominant allele responsible for a number of rare horse coat colors. The most distinctive traits of horses with the champagne gene are the hazel eyes and pinkish, freckled skin, which are bright blue and bright pink at birth, respectively...

.
A DNA test can now identify the Lp gene, though a combination of pedigree knowledge and coat characteristics also help.

While both heterozygous and homozygous Lp horses possess the aforementioned characteristics, heterozygotes and homozygotes differ significantly in the presence of true spots. True leopard spots are produced only by the Lp gene, and directly reflect the underlying coat color (bay, black, gray, cremello, red dun, and so on). Since these spots match the coat color, they are not visible unless the surrounding pigment is removed. As a rule, heterozygous leopards have larger, more abundant spots, while homozygotes have smaller, scarcer spots.

White patterning

There is at least one genetically-controlled type of white patterning that is strictly associated with the leopard complex. These white patterns permit the spots associated with the leopard complex to become visible. Other white patterns, such as tobiano

Tobiano

Tobiano is a spotted color pattern commonly seen in Pinto horses, produced by a dominant gene. The tobiano gene produces white-haired, pink-skinned patches on a base coat color. The coloration is present from birth and does not change throughout the horse's lifetime, unless the horse also carries...

 or white leg markings, obscure leopard spots. A certain amount of leopard-associated white patterning may be present at birth. Temporal changes in the amount of white patterning are discussed below. Leopard-associated white patterning is usually symmetrical and originates over the hips. A proposed gene, PATN-1, may be responsible for the most familiar expressions of white: heterozygotes possessing common-size "blankets" and homozygotes possessing extensive "blankets" that may affect the entire coat. Even horses with extensive white usually retain dark colored regions just above the hooves, on the knees and hocks, stifles and elbows, hips and points of shoulder, the tail, mane, and the bony parts of the face. The smallest amount of white patterning is just a sprinkling of white over the hips.

Leopard-associated roaning

Just as there is white patterning specifically associated with the leopard complex, there is a type of progressive roaning that is unrelated to graying out

Gray (horse)

Gray or grey is a coat color of horses characterized by progressive silvering of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike many depigmentation genes, gray does not affect skin or eye color Their adult hair coat is white, dappled, or white intermingled...

 or true roan

Roan (horse)

Roan is a horse coat color pattern characterized by an even mixture of colored and white hairs on the body, while the head and "points"—lower legs, mane and tail—are more solid-colored. The roan pattern is dominantly-inherited, and is found in many horse breeds...

. Horses with coat patterns within the leopard complex are known for their mystifying coat changes. This unusual characteristic is due at least in part to leopard roaning, also called "varnish roaning." While the gray gene only affects the hair, some horses with the Lp gene will progressively lose pigment in both the skin and hair as they age. Also unlike graying out, the leopard spots are not affected by this roaning process. Neither are the "bony prominences" strongly affected. As a varnish roan horse lightens, the leopard spots indistinguishable from the rest of the coat become visible. Some horses without any dense white patterning at birth seem to spontaneously develop into white, leopard-spotted horses with maturity. Varnishing is more common among Appaloosa horses, and less common among Norikers and Knabstruppers, whose breeders feel it undesirable.

Interactions and terminology

Like much of coat color genetics, commonly used terms do not necessarily correspond to precise genetic states. Nevertheless, terminology can reveal a lot about the genetic interactions surrounding the leopard complex.

• Heterozygous Lp/lp horses with extensive white patterning at birth are white with large, self-colored spots. They are termed "leopard" if fully white, "near-leopard" if not. By the action of varnish roan, a near-leopard may in time become nearly indistinguishable from a full leopard.
• Heterozygous Lp/lp horses with less white patterning are described by the size of their "blanket" and the presence of spots: spotted blanket over loin and hips, for example. Again, these horses may varnish with age.
• Homozygous Lp/Lp horses with extensive white patterning at birth are white with tiny, sparse spots or none at all. In most languages, such foals are called "white-born" but the term familiar to most English speakers is "fewspot (leopard)."
• Homozygous Lp/Lp horses with less than extensive white patterning at birth possess dense white blankets and are called "snowcap."
• Heterozygous Lp/lp and homozygous Lp/Lp horses with only a tiny amount of white patterning may not possess enough white to reveal large or small spots. A sprinkling of white patterning over the hips is called a "snowflake" pattern. Such tiny blankets may varnish and grow.
• Heterozygous Lp/lp horses and homozygous Lp/Lp horses, in the absence of dense white patterning, appear much the same. That is, unless they begin to varnish. As the coat becomes more and more white, spots may become visible. A homozygous Lp/Lp horse, with only tiny spots, may simply develop this unique roaning pattern and is called "frosted" or "marble." A heterozygote may eventually show conspicuous leopard spots.

Patterns

Base colors are overlain by various spotting patterns, which are variable and often do not fit neatly into a specific category. These patterns are described as follows:

Pattern	Description	Image
Blanket or snowcap	A solid white area normally over, but not limited to, the hip area with a contrasting base color.
Spots	general term that refers to a horse which has white or dark spots over all or a portion of its body.
Blanket with spots	a white blanket which has dark spots within the white. The spots are usually the same color as the horse's base color.
Leopard	Considered an extension of a blanket to cover the whole body. A white horse with dark spots that flow out over the entire body.
Few Spot Leopard	A mostly white horse with a bit of color remaining around the flank, neck and head.
Snowflake	A horse with white spots, flecks, on a dark body. Typically the white spots increase in number and size as the horse ages.
Appaloosa Roan, Varnish roan Varnish roan Varnish roan describes a horse with coloration similar to roan, but with some changes in color over the years, though not to the extreme of a gray. This type of roaning only occurs in conjunction with the Leopard complex. Varnish roans are born with a dark base coat color, usually with some spotting... or Marble	A distinct version of the leopard complex. Intermixed dark and light hairs with lighter colored area on the forehead, jowls and frontal bones of the face, over the back, loin and hips. Darker areas may appear along the edges of the frontal bones of the face as well and also on the legs, stifle, above the eye, point of the hip and behind the elbow. The dark points over bony areas are called "varnish marks" and distinguish this pattern from a traditional roan Roan (horse) Roan is a horse coat color pattern characterized by an even mixture of colored and white hairs on the body, while the head and "points"—lower legs, mane and tail—are more solid-colored. The roan pattern is dominantly-inherited, and is found in many horse breeds... .
Mottled	A fewspot leopard that is completely white with only mottled skin showing.
Roan Blanket or Frost	Horses with roaning over the croup and hips. The blanket normally occurs over, but is not limited to, the hip area.
Roan Blanket With Spots	refers to a horse with a roan blanket which has white and/or dark spots within the roan area.

The Lp gene

Although the spotting and roaning patterns that make up the leopard complex sometimes appear very different from each other, the ability of leopard-spotted horses to produce the full spectrum of patterns, from mottled skin to roaning to more leopard-spotted offspring, has long suggested that a single gene was responsible. This gene was termed Lp for "leopard complex" by Dr. D. Phillip Sponenberg in 1982, and was described as an autosomal, incomplete dominant gene. Horses without the gene (lplp) were solid-colored, those with two copies of the gene (homozygous or LpLp) were usually "fewspots", while those with a single copy of the gene (heterozygous or Lplp) ranged from mere mottled skin to full leopard.

In 2004, Lp was assigned to equine chromosome 1 (ECA1) by a team of researchers. Four years later, this team mapped the Lp gene to a transient receptor potential channel gene, TRPM1

TRPM1

Transient receptor potential cation channel subfamily M member 1 is a protein that in humans is encoded by the TRPM1 gene.- Function :The protein encoded by this gene is similar to the transient receptor potential calcium channel family members...

 or Melastatin 1 (MLSN1). As yet, the etiology of this condition remains poorly understood.

In 2011, it was announced that an allele associated with Lp was identified in DNA samples collected from prehistoric horses. This finding represents evidence for the presence of leopard complex spotting in prehistoric wild horse

Wild Horse

The wild horse is a species of the genus Equus, which includes as subspecies the domesticated horse as well as the undomesticated Tarpan and Przewalski's Horse. The Tarpan became extinct in the 19th century, and Przewalski's Horse was saved from the brink of extinction and reintroduced...

 populations. The ancient origin of the allele may explain the presence of spotted horse paintings in paleolithic cave art.

Vision issues

Congenital stationary night blindness

Nyctalopia

Nyctalopia is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition...

 is an opthalmologic disorder

Ophthalmology

Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...

 in horses which is present at birth (congenital), non-progressive (stationary) and affects the animal's vision in conditions of low lighting. Horses with CSNB may be hesitant to enter dimly-lit places - such as indoor arenas, dark stalls, or trailers - and be apprehensive when in such conditions, which may interfere with handling or riding. CSNB is usually diagnosed based on the owner's observations, but some horses have visibly abnormal eyes: poorly-aligned eyes (dorsomedial strabismus) or involuntary eye movement (nystagmus). The condition can be confirmed using electroretinography

Electroretinography

Electroretinography measures the electrical responses of various cell types in the retina, including the photoreceptors , inner retinal cells , and the ganglion cells. Electrodes are usually placed on the cornea and the skin near the eye, although it is possible to record the ERG from skin electrodes...

, from which a "negative ERG" indicates CSNB. While the retina is a normal shape, the nerve signal triggered when light reaches rod cells does not reach the brain. Rod cells in the retina are connected to bipolar cells, which transmit the nerve impulse to the next set of neurons. It is thought that these cells fail to undergo the basic chemical reaction for nerve impulse transmission, which involves shuttling of calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 (Ca²⁺).

Congenital stationary night blindness has been linked with the leopard complex since the 1970s. The presence of CSNB in non-leopard breeds and horses suggested that the two conditions might be located on close, but separate genes. However, one study used ERG findings to diagnose all the homozygous Lp subjects with CSNB, while all heterozygotes and non-Lp horses were free from the disorder. The gene to which Lp has now been localized encodes a protein that channels calcium ion

Ion

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s, a key factor in the transmission of nerve impulses. This protein, which is found in the retina and the skin, existed in fractional percentages of the normal levels in homozygous Lp/Lp horses. A 2008 study theorizes that both CSNB and leopard complex spotting patterns are linked to the TRPM1

TRPM1

Transient receptor potential cation channel subfamily M member 1 is a protein that in humans is encoded by the TRPM1 gene.- Function :The protein encoded by this gene is similar to the transient receptor potential calcium channel family members...

 gene.
Equine Recurrent Uveitis

Equine Recurrent Uveitis

Equine Recurrent Uveitis, is an acute, non-granulomatous inflammation of the uveal tract of the eye, occurring commonly in horses of all breeds, worldwide. The causative factor is not known, but several pathogeneses have been suggested. It is the most common cause of blindness in horses...

 (ERU) is also present in the breed. Appaloosas have an eightfold greater risk of developing Equine Recurrent Uveitis

Equine Recurrent Uveitis

Equine Recurrent Uveitis, is an acute, non-granulomatous inflammation of the uveal tract of the eye, occurring commonly in horses of all breeds, worldwide. The causative factor is not known, but several pathogeneses have been suggested. It is the most common cause of blindness in horses...

 (ERU) than all other breeds combined. Up to 25% of all horses with ERU may be Appaloosas. Uveitis

Uveitis

Uveitis specifically refers to inflammation of the middle layer of the eye, termed the "uvea" but in common usage may refer to any inflammatory process involving the interior of the eye....

 in horses has many causes, including eye trauma, disease, and bacterial, parasitic and viral infections, but ERU is characterized by recurring episodes of uveitis, rather than a single incident. If not treated, ERU can lead to blindness, which occurs more often in Appaloosas than in other breeds. Up to 80% of all uveitis cases are found in Appaloosas, with physical characteristics including light colored coat patterns, little pigment around the eyelids and sparse hair in the mane and tail denoting more at-risk individuals. Researchers may have identified a gene region containing an allele

Allele

An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...

 that makes the breed more susceptible to the disease.

Prevalence

The Appaloosa horse is the breed best-known for the leopard complex patterns, though the complex characterizes the Pony of the Americas

Pony of the Americas

The Pony of the Americas, or the POA, was developed to be a children’s pony. The breed’s origins are in America, where an Iowa breeder accidentally crossed a Shetland stallion with an Arabian/Appaloosa mare to produce a pony-sized mount with leopard complex spotting.-Breed Characteristics:The POA...

, Colorado Ranger

Colorado Ranger

The Colorado Ranger is a horse breed named for its Colorado High Plains origins in the United States of America.-Characteristics:The registers horses that can be traced back to one of the two stallions and which also meet additional registration requirements. The breed traces back to one of the...

, Tiger Horse

Tiger Horse

Tiger horses are gaited, spotted horses with a coat color much like the Appaloosa. The tiger horse can exhibit various ambling gaits including various lateral gaits called the "Glider Gait" or Indian shuffle, stepping pace, and running walk, as well as the diagonal Fox Trot...

, British Spotted Pony and the Knabstrupperper breeds. The gene is also relatively common in the Miniature horse

Miniature horse

Miniature horses are found in many nations, particularly in Europe and the Americas. The designation of miniature horse is determined by the height of the animal, which, depending on the particular breed registry involved, is usually less than as measured at the last hairs of the mane, which are...

 and Falabella

Falabella (horse)

The Falabella miniature horse is one of the smallest breeds of horse in the world, seldom taller than eight hands in height at the withers. The Falabella is a rare breed, with only a few thousand individuals existing worldwide...

 breeds, the Spanish Mustang

Spanish Mustang

The Spanish Mustang is a horse breed of historical importance. They descend from horses introduced from Spain during the early conquest of the Americas. They are a type that today is mostly or wholly now extinct in Spain...

, the Noriker

Noriker horse

The Noriker horse, also called the Norico-Pinzgauer and historically known as the Pinzgauer horse, is a moderately heavy Austrian draught horse breed. The Noriker is considered indigenous to the central Alpine region of Europe, and is believed to have originated around the highest mountain of...

 and the related South German Coldblood. The existence of leopard-spotted coats among Asian breeds such as the Karabair

Karabair

The Karabair breed is a very old breed based on ancient stock that has been documented as being in the Uzbekistan area before the Christian era.-History:...

 and Mongolian Altai

Altai (horse)

The Altai is a horse breed developed in the Altai Mountains of Central Asia.- Characteristics :The Altai has a head with a slightly dished profile, set on a relatively short neck. They have a strong back, a well-developed croup, and short cannon bones...

 has been recorded since ancient times, and suggests that the gene is very old. Leopard complex patterns exist in very low frequencies among American Quarter Horse

American Quarter Horse

The American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other breeds of horses in races of a quarter mile or less; some individuals have been clocked at speeds up to 55 mph...

s, Connemaras

Connemara pony

The Connemara pony is a pony breed originating in Ireland. They are known for their athleticism, versatility and good disposition. The breed makes excellent show ponies.-History:...

 and Welsh Ponies

Welsh Pony

The Welsh Pony and Cob are closely related horse breeds including both pony and cob types, which originated in Wales in the United Kingdom...

.