Roan is a coat color found in many animals, including horses, cattle, antelope, cats and dogs. It is defined generally as an even mixture of white and pigmented hairs that do not "gray out" or fade as the animal ages. There are a variety of genetic conditions which produce the colors described as "roan" in various species.
A dilution gene is any one of a number of genes that act to create a lighter coat color in living creatures. There are many examples of such genes:
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.
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.
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.
At right is displayed the color traditionally called liver.
Canine terminology in this article refers only to dog terminology, specialized terms describing the characteristics of various external parts of the domestic dog, as well as terms for structure, movement, and temperament. This terminology is not typically used for any of the wild species or subspecies of wild wolves, foxes, coyotes, dholes, jackals or the basal caninae. Dog terminology is often specific to each breed or type of dog. Breed standards use this terminology in the description of the ideal external appearance of each breed, although similar characteristics may be described with different terms in different breeds.
The silver or silver dapple (Z) gene is a dilution gene that affects the black base coat color and is associated with Multiple Congenital Ocular Abnormalities. It will typically dilute a black mane and tail to a silvery gray or flaxen color, and a black body to a chocolaty brown, sometimes with dapples. It is responsible for a group of coat colors in horses called "silver dapple" in the west, or "taffy" in Australia. The most common colors in this category are black silver and bay silver, referring to the respective underlying coat color.
Equine coat color genetics determine a horse's coat color. Many colors are possible, but all variations are produced by changes in only a few genes. Bay is the most common color of horse, followed by black and chestnut. A change at the agouti locus is capable of turning bay to black, while a mutation at the extension locus can turn bay or black to chestnut.
Merle is a genetic pattern in a dog's coat and alleles of the PMEL gene. It results in different colors and patterns and can affect any coats. The allele creates mottled patches of color in a solid or piebald coat, blue or odd-colored eyes, and can affect skin pigment as well. Two types of colored patches generally appear in a merle coat: brown/liver and black. Associated breeds include Carea Leonés, Australian Shepherds and Catahoula Leopard Dogs. Health issues are more typical and more severe when two merle-patterned dogs are bred together.
Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them.
A tabby cat, or simply tabby, is any domestic cat with a distinctive M-shaped marking on its forehead, stripes by its eyes and across its cheeks, along its back, around its legs and tail, and characteristic striped, dotted, lined, flecked, banded, or swirled patterns on the body: neck, shoulders, sides, flanks, chest, and abdomen. The four known distinct patterns, each having a sound genetic explanation, are the mackerel, classic or blotched, ticked, and spotted tabby patterns.
A calico cat is a domestic cat of any breed with a tri-color coat. The calico cat is most commonly thought of as being 25% to 75% white with large orange and black patches; however, they may have other colors in their patterns. Calicoes are almost exclusively female except under rare genetic conditions.
The genetic basis of coat colour in the Labrador Retriever has been found to depend on several distinct genes. The interplay among these genes is used as an example of epistasis.
Acromelanism or colorpoint is a genetically determined, temperature-dependent pigmentation pattern, with full expression only occurring on legs, ears, tail, face and scrotum. It is most recognized as the coloration of Siamese and related breeds of cat, but can be found in dogs, rabbits, rats, mice, sheep, guinea pigs, minks, and gerbils. It is a specific type of point coloration.
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.
A melanistic mask is a dog coat pattern that gives the appearance of a mask on the dog's face. The hairs on the muzzle, and sometimes entire face or ears, are colored by eumelanin instead of pheomelanin pigment. Eumelanin is typically black, but may instead be brown, dark gray, or light gray-brown. Pheomelanin ranges in color from pale cream to mahogany. The trait is caused by M264V (EM), a completely dominant allele (form) of the melanocortin 1 receptor gene.
Tortoiseshell is a cat coat coloring named for its similarity to tortoiseshell pattern. Like tortoiseshell-and-white or calico cats, tortoiseshell cats are almost exclusively female. Male tortoiseshells are rare and are usually sterile.
Dogs have a wide range of coat colors, patterns, textures and lengths. Dog coat color is governed by how genes are passed from dogs to their puppies and how those genes are expressed in each dog. Dogs have about 19,000 genes in their genome but only a handful affect the physical variations in their coats. Most genes come in pairs, one being from the dog's mother and one being from its father. Genes of interest have more than one expression of an allele. Usually only one, or a small number of alleles exist for each gene. In any one gene locus a dog will either be homozygous where the gene is made of two identical alleles or heterozygous where the gene is made of two different alleles.
The agouti gene, the Agouti-signaling protein (ASIP) is responsible for variations in color in many species. Agouti works with extension to regulate the color of melanin which is produced in hairs. The agouti protein causes red to yellow pheomelanin to be produced, while the competing molecule α-MSH signals production of brown to black eumelanin. In wildtype mice, alternating cycles of agouti and α-MSH production cause agouti coloration. Each hair has bands of yellow which grew during agouti production, and black which grew during α-MSH production. Wildtype mice also have light-colored bellies. The hairs there are a creamy color the whole length because the agouti protein was produced the whole time the hairs were growing.
