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:
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.
Point coloration is animal coat coloration with a pale body and relatively darker extremities, i.e. the face, ears, feet, tail, and scrotum. It is most recognized as the coloration of Siamese and related breeds of cat, but can be found in dogs, rabbits, rats, sheep, guinea pigs and horses as well.
A gray horse has a coat color characterized by progressive depigmentation of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike some equine dilution genes and some other genes that lead to depigmentation, gray does not affect skin or eye color. Gray horses may be born any base color, depending on other color genes present. White hairs begin to appear at or shortly after birth and become progressively more prevalent as the horse ages as white hairs become intermingled with hairs of other colors. Graying can occur at different rates—very quickly on one horse and very slowly on another. As adults, most gray horses eventually become completely white, though some retain intermixed light and dark hairs.
The cream gene is responsible for a number of horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut will become palomino if they are heterozygous, having one copy of the cream gene, or cremello, if they are homozygous. Similarly, horses with a bay base coat and the cream gene will be buckskin or perlino. A black base coat with the cream gene becomes the not-always-recognized smoky black or a smoky cream. Cream horses, even those with blue eyes, are not white horses. Dilution coloring is also not related to any of the white spotting patterns.
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. The coat color is also affected: any hairs that would have been red are gold, and any hairs that would have been black are chocolate brown. If a horse inherits the champagne gene from either or both parents, a coat that would otherwise be chestnut is instead gold champagne, with bay corresponding to amber champagne, seal brown to sable champagne, and black to classic champagne. A horse must have at least one champagne parent to inherit the champagne gene, for which there is now a DNA test.
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.
The dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene lightens most of the body while leaving the mane, tail, legs, and primitive markings the shade of the undiluted base coat color. A dun horse always has a dark dorsal stripe down the middle of its back, usually has a darker face and legs, and may have transverse striping across the shoulders or horizontal striping on the back of the forelegs. Body color depends on the underlying coat color genetics. A classic "bay dun" is a gray-gold or tan, characterized by a body color ranging from sandy yellow to reddish brown. Duns with a chestnut base may appear a light tan shade, and those with black base coloration are a smoky gray. Manes, tails, primitive markings, and other dark areas are usually the shade of the undiluted base coat color. The dun gene may interact with all other coat color alleles.
The Fjord or Norwegian Fjord Horse is a relatively small but very strong horse breed from the mountainous regions of western Norway. It is an agile breed of light draught horse build. It is always dun in colour, with five variations in shade recognised in the breed standard. One of the world's oldest breeds, it has been used for hundreds of years as a farm horse in Norway, and in modern times is popular for its generally good temperament. It is used both as a harness horse and under saddle.
The Silver Brumby series is a collection of fiction children's books by Australian author Elyne Mitchell. They recount the life and adventures of Thowra, a magnificent palomino brumby stallion, and his descendants, and are set in the Snowy Mountains and southern regions of Australia.
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. Chestnut is characterized by the absolute absence of true black hairs. It is one of the most common horse coat colors, seen in almost every breed of horse.
Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them.
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.
Black is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and it is not uncommon to mistake dark chestnuts or bays for black.
The American Cream Draft is an American breed of draft horse, characterized by the cream or "gold champagne" color of its coat. It was developed in Iowa during the early twentieth century from a cream-colored mare named Old Granny. A breed registry was formed in 1944 but became inactive for several decades when breed numbers dropped due to the mechanization of farming. It was reactivated in 1982 and population numbers have slowly grown since then. It is a rare breed: its conservation status is considered critical by The Livestock Conservancy and the Equus Survival Trust.
Smoky black or black carrying cream is a coat color of horses which has the same phenotype as black. Smoky black is produced by the action of a heterozygous cream gene on an underlying black coat color. Therefore, smoky black is a member of the cream family of coat color dilutions, and found in horse populations that have other cream-based colors such as palomino, buckskin, perlino, cremello and smoky cream. All smoky blacks must have at least one parent with the cream gene, and a smoky black can only be verified through DNA testing or parentage. Smoky black has been mistaken for faded black, dark bay or brown, grullo or even liver chestnut.
The Pearl gene, also known as the "Barlink factor", is a dilution gene at the same locus as the cream gene, which somewhat resembles the cream gene and the champagne gene but is unrelated to champagne. It is a somewhat rare dilution gene found in the American Quarter Horse, American Paint Horse, and Peruvian Paso. The same mutation appears in Iberian horse breeds such as the Lusitano and Andalusian. The existence of the pearl gene in Quarter Horses and Paints is probably because these breeds have some Iberian ancestors.
Flaxen is a genetic trait in which the mane and tail of chestnut-colored horses are noticeably lighter than the body coat color, often a golden blonde shade. Manes and tails can also be a mixture of darker and lighter hairs. Certain horse breeds such as the Haflinger carry flaxen chestnut coloration as a breed trait. It is seen in chestnut-colored animals of other horse breeds that may not be exclusively chestnut.
