Acromelanism is a genetic condition that results in pigmentation being affected by temperature. It results in point coloration where the extremities of an animal are a different colour to the rest of the body. It is commonly known for the coloration of Siamese [1] and related breeds of cat, but can be found in many other species including dogs, rabbits, rats, mice, guinea pigs, minks, and gerbils. [2] It is a specific type of point coloration.
Colorpoint patterns are where the extremities (paws, face, ears and tail) of the animal are colored differently to the rest of the body. The areas with different color may be referred as 'points' or being 'pointed'. [3] Color can spread to the rest of the body, but is concentrated on the extremities.
Colorpoint patterns occur due to acromelanism, which is a type of partial albinism where pigmentation is affected by temperature. [3] Cold temperaments trigger pigment development while warm temperatures decrease pigment development. The extremities are colder than the rest of the body which is why they darken.
The C locus in mammals is most often associated with the TYR gene, which controls the production of the tyrosinase enzyme that produces melanin. [4]
The color point allele is at the C locus, where some forms of typical albinism are also located. Point is recessive for all animals. In cats, two copies of cs, one from each parent, are needed for points to be expressed.
Point coloration in cats originated in the Siamese and closely related Asian breeds, and is found in many Western-developed modern breeds. It is a form of partial albinism resulting from a mutation of the albino gene that affects tyrosinase, an enzyme involved with melanin production. The mutated enzyme is thermolabile; it fails to work at normal body temperatures, but becomes active in cooler areas of the skin. [5] [3] As a result, dark pigment is limited to the coldest areas of the body, that is, the extremities. [3] Pointed kittens are born white, due to the warmth of uterus of the queen. As the kitten ages, the cooler areas darken while warmer areas remain cream to white in color. Colorpoints can usually be observed at four weeks. [3]
As the expression of the gene responsible for the pointed pattern is regulated by temperature, pointed cats who live in cooler environments often show increased darkening of their fur relative to cats who live in warmer climates, in some cases the entire coat will darken. Shaving a cat can also change the colour of the coat. Conditions that affect the temperature of the animal can change the colour too, e.g. pyrexia can inactivate tyrosinase and result in new growth being uncoloured and obesity may result in the whole body turning dark due to the decreased skin temperature. [3]
Because of the pigment restriction caused by the temperature sensitive tyrosinase, pointed cats' eyes are always shades of blue because the blue layer in the eye common to all cats is not covered by another color. The back of the eye also lacks pigment, giving colorpoint cats' pupils an eerie red and silver reflection in the dark, unlike a normally pigmented cat's shining silver-green or -blue.
The lynx point pattern is formed by mating a colorpoint cat with a tabby cat (or breeding cats that already possess the lynx point pattern). It is characterized by a mixture of the darkening (reduced) of point coloration with distinct tabby striping on the head, tail, and legs, and an otherwise uniform and comparatively pale body. It is an accepted pattern in some cat registries, but not others, for particular breeds (mostly Siamese-related).
Point coloration is inherent to the Siamese breed and some other closely related breeds but with most other breeds the colorpoints (including lynx) were brought into some breed lines long after their establishment, but there are exceptions. For example, lynx point was a feature of some of the foundation stock of the Siberian, now called the Neva Masquerade. [6]
Different colours have special names: brown is known as 'seal point', red/orange as 'flame point', blue as 'blue point', and lavender as 'lilac point'. For the Tonkinese cat terms such champagne and platinum are used.
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Rarely, dogs (Canis familiaris) are documented with point coloration or acromelansim. [7] Recent documented evidence about acromelanism in dogs has only existed since 2017, when the first colorpoint dachshund was reported in the Czech Republic. More dogs have appeared since then, with the majority from the eastern Eurasian region and Canada. Genotyping the aforementioned dachshund revealed a mutation in the tyrosinase gene that results in a recessive colorpoint allele. [8] [9]
Some rabbits that appear to be pointed white lack the red eyes, which indicates they are of different breeding. The following such coat colors are examples of those created, not with the ch gene, but with the cchl, cchd, or cchm gene in conjunction with the e gene:[ citation needed ]
No pointed white rabbit can produce orange pigment; therefore, the points are always either black, blue, chocolate, or lilac.[ citation needed ] The resulting point coloration is sometimes in conjunction with a coat pattern, such as: white agouti, marten, broken, Vienna, or harlequin. (Such coats may not be recognized for showing.)
Breeds of rabbit that include varieties with point coloration include: [10] [11]
The C - Albino locus gene causes dilution of yellow and black coloration, causing Himalayan or Siamese markings depending on the allele is affected.
Point colors in rats include:
There is only one type of guinea pig with a pointed coat. It is called the Himalayan, has either Black (a very dark brown) or Chocolate, tipped on the Ears, Nose, and Feet.
The Siamese cat is one of the first distinctly recognised breeds of Asian cat. It derives from the Wichianmat landrace. The Siamese cat is one of several varieties of cats native to Thailand. The original Siamese became one of the most popular breeds in Europe and North America in the 19th century. Siamese cats have a distinctive colourpoint coat, resulting from a temperature-sensitive type of albinism.
Tonkinese is a domestic cat breed produced by crossbreeding between the Siamese and Burmese. Members of the breed are distinguished by a pointed coat pattern in a variety of colors. In addition to the modified coat colors of the "mink" pattern, which is a dilution of the point color, the breed is now being shown in the foundation-like Siamese and Burmese colors: pointed with white and solid overall (sepia).
Cat coat genetics determine the coloration, pattern, length, and texture of feline fur. The variations among cat coats are physical properties and should not be confused with cat breeds. A cat may display the coat of a certain breed without actually being that breed. For example, a Neva Masquerade could wear point coloration, the stereotypical coat of a Siamese.
The Ragdoll is a breed of cat with a distinct colorpoint coat and blue eyes. Its morphology is large and weighty, and it has a semi-long and silky soft coat. American breeder Ann Baker developed Ragdolls in the 1960s. They are best known for their docile, placid temperament and affectionate nature. The name Ragdoll is derived from the tendency of individuals from the original breeding stock to go limp and relaxed when picked up. The breed is particularly popular in both the United Kingdom and the United States.
The Javanese, also known as the ColorpointLonghair in some registries, is a variety of purebred domestic cat.
A piebald or pied animal is one that has a pattern of unpigmented spots (white) on a pigmented background of hair, feathers or scales. Thus a piebald black and white dog is a black dog with white spots. The animal's skin under the white background is not pigmented.
The Snowshoe is a rare breed of domestic cat originating in the United States of America in the 1960s. The Snowshoe is a short-haired bicolour colourpoint breed. Snowshoes were first produced when a Siamese breeder's cat gave birth to three kittens with white feet. The breeder, Dorothy Hinds-Daugherty, then began a breeding program to produce what were originally called "Silver Laces", crossing the strangely marked Siamese cats with bicolour American Shorthair cats and other breeds. Despite having existed for 45 years, Snowshoes are rare due to the difficulty of reproducing the correct coat markings.
Bay is a hair coat color of horses, characterized by a reddish-brown or brown body color with a black point coloration on the mane, tail, ear edges, and lower legs. Bay is one of the most common coat colors in many horse breeds.
Ojos Azules was a breed of shorthaired domestic cat with unusual blue or odd eyes caused by a dominant blue eye (DBE) genetic mutation. The breed came in all coat colors; however, only particolors, colorpoints, and intermediate colors with a characteristic white tail tip were permitted. The breed also had a semi-longhaired coat variety, the Ojos Azules Longhair. Due to the lethal side effects of the Ojos Azules gene, breeders stopped working with this blue eye mutation.
Points are specific areas of an animal coat that are colored differently from the main body colorations. Point coloration may be represented by a pale body color and relatively darker extremities, such as face, ears, feet, tail, and external sex organs, as seen on Siamese cats. However, colored points can be found in many mammal species and some points are lighter than the main body color.
The Colorpoint Shorthair is a variety of Siamese cat. The only major registries to recognise them are the Cat Fanciers' Association (CFA) and the World Cat Federation (WCF). This breed was established from breeding American Shorthairs with the Siamese to produce different point colors, beyond the four standard Siamese colors.
A white horse is born predominantly white and stays white throughout its life. A white horse has mostly pink skin under its hair coat, and may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white (W) genes, are rare. Most horses that are commonly referred to as "white" are actually "gray" horses whose hair coats are completely white. Gray horses may be born of any color and their hairs gradually turn white as time goes by and take on a white appearance. Nearly all gray horses have dark skin, except under any white markings present at birth. Skin color is the most common method for an observer to distinguish between mature white and gray horses.
Cat genetics describes the study of inheritance as it occurs in domestic cats. In feline husbandry it can predict established traits (phenotypes) of the offspring of particular crosses. In medical genetics, cat models are occasionally used to discover the function of homologous human disease genes.
Colourpoint or colorpoint may refer to:
Amelanism is a pigmentation abnormality characterized by the lack of pigments called melanins, commonly associated with a genetic loss of tyrosinase function. Amelanism can affect fish, amphibians, reptiles, birds, and mammals including humans. The appearance of an amelanistic animal depends on the remaining non-melanin pigments. The opposite of amelanism is melanism, a higher percentage of melanin.
The Himalayan rabbit is a small breed of rabbit with similar markings to the Californian rabbit. The body is white with colored points, recognized colors are black, blue, chocolate and lilac.
The Balinese is a long-haired breed of domestic cat with Siamese-style point coloration and sapphire-blue eyes. The Balinese is also known as the purebred long-haired Siamese since it originated as a natural mutation of that breed and hence is essentially the same cat but with a medium-length silky coat and a distinctively plumed tail.
Heterotopy is an evolutionary change in the spatial arrangement of an animal's embryonic development, complementary to heterochrony, a change to the rate or timing of a development process. It was first identified by Ernst Haeckel in 1866 and has remained less well studied than heterochrony.
The Velveteen Lop is a breed of lop-eared rabbit developed from Mini Rex and English Lop ancestry in the United States from the late 1980s through early 1990s. It is the first American rabbit breed to combine lopped ears and rex fur. Velveteens are known to have friendly, gentle personalities. They are medium-sized rabbits weighing 5 to 7 pounds when fully grown and come in a wide variety of coat colors.