A dilution gene is any one of a number of

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

s that act to create a lighter coat color in living creatures. There are many examples of such genes:

General

Diluted coat colors have

melanocyte Melanocytes are melanin-producing neural-crest, neural crest-derived cell (biology), cells located in the bottom layer (the stratum basale) of the skin's epidermis (skin), epidermis, the middle layer of the eye (the uvea), the inner ear, vagina ...

s, but vary from darker colors due to the concentration or type of these pigment-producing cells, not their absence. Pigment dilution, sometimes referred to as hypomelanism, has been called leucism, albinism (perfect, impartial, or dilute), ghosting, paling, and isabellinism. *

Albinism Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and reddish pink or blue eyes. Individuals with the condition are referred to as albinos. Varied use and interpretation of ...

describes a condition where pigment cells synthesize little or no pigment *

Leucism Leucism () is a wide variety of conditions that result in partial loss of pigmentation in an animal—causing white, pale, or patchy coloration of the skin, hair, feathers, scales, or cuticles, but not the eyes. It is occasionally spelled ''le ...

describes a condition that creates loss of pigment cells

Cats

Cat coat genetics 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 actu ...

discusses many dilution genes in

cat The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...

Dogs

In dogs, a mutation of the ''MLPH'' locus known as the dilute gene causes eumelanin to lighten while pheomelanin remains almost unchanged. Dogs of some breeds with the dilute gene often suffer from colour dilution alopecia (CDA).

Appearance

Of the colour shades found in the coat of dogs, the light brown caused by

pheomelanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the Biological pigment, pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melan ...

is hardly affected. Black

eumelanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...

is lightened to a grey called "blue". Chocolate brown eumelanine is lightened to the typical colour of the

Weimaraner The is a German breed of hunting dog of medium to large size, with history going back at least to the nineteenth century. It originated in the area of the city of Weimar (then in Saxe-Weimar-Eisenach, now in the state of Thuringia), for which ...

. Dangerousdream.jpg,

Great Dane The Great Dane is a German list of dog breeds, breed of large mastiff-sighthound, which descends from hunting dogs of the Middle Ages used to hunt bears, wild boar, and deer. They were also used as guardian dogs of German nobility. It is one o ...

s lightened from black to blue by the dilute gene. Doberman Pinschers black and blue.jpg, Doberman: black with tan in the back, blue with tan in the front. The light brown areas were hardly lightened at all CaneCorso (12).jpg, Blue-light brown

brindle Brindle is a coat (animal), coat coloring pattern in animals, particularly dogs, cattle, guinea pigs, cats, and, rarely, horses. It is sometimes described as "tiger-striped", although the brindle pattern is more subtle than that of a tiger's co ...

dog Hund - brindle.jpg, For comparison without dilute gene: black-light brown brindle dog Weimaraner Freika-2.jpg,

Silver Labrador Retriever Cooper.jpg, Silver Labrador Colour Dilution Alopecia (CDA) in Silver Labrador dog.jpg, Colour dilution alopecia

Genetics

The dilute gene d is recessive to the

wild type The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, " ...

allele D. A gene test can be used to determine a dog's

genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

concerning genes for pigmentation. In some

dog breed A dog breed is a particular type of dog that was purposefully bred by humans to perform specific tasks, such as herding, hunting, and guarding. Dogs are the most variable mammal on Earth, with artificial selection producing upward of 360 globall ...

s lightened by the dilute gene, the mutation d is associated with color dilution alopecia (CDA). Since not all breeds in which the gene occurs exhibit these problems, it is suspected that there may be a second previously unknown mutation of the MLPH gene.Samantha L. van Buren, Katie L. Minor et al.:
A Third MLPH Variant Causing Coat Color Dilution in Dogs
'. In: Genes, Vol. 11, Issue 6, June 2020. Every dog has two

allele An allele is a variant of the sequence of nucleotides at a particular location, or Locus (genetics), locus, on a DNA molecule. Alleles can differ at a single position through Single-nucleotide polymorphism, single nucleotide polymorphisms (SNP), ...

s - one from the sire and one from the dam. The

gene expression Gene expression is the process (including its Regulation of gene expression, regulation) by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, proteins or non-coding RNA, ...

depends on the

# DD: Both sire and dam have inherited the wild type allele. The coat is not lightened. # Dd: Either sire or dam have inherited the

for dilution. However, the dilution of colour is not visible in the

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...

- the dog has the same coat colour as a DD dog. # dd: Sire and dam have inherited the allele for the dilute colour expression. The black areas of the coat are lightened to blue, dogs additionally lightened by the gene on the B locus take on the colour typical of the Weimaraner. According to the Mendelian Rules, an average of 25% of the puppies receive the

homozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mos ...

gene combination dd if both parents are

genetic carrier A hereditary carrier (genetic carrier or just carrier), is a person or other organism that has inherited a recessive allele for a genetic trait or mutation but usually does not display that trait or show symptoms of the disease. Carriers are, ho ...

Horses

Equine coat color genetics 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 horse, Bay is the most common color of horse, followed by black and chestnut. A change at the ...

discusses color genes in

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 mi ...

s, including a brief description of dilution genes *

Equine coat color Horses exhibit a diverse array of coat colors and distinctive horse markings, markings. A specialized vocabulary has evolved to describe them. While most horses remain the same coat color throughout life, some undergo gradual color changes as th ...

describes various colors in horses *

Cream gene The cream gene is responsible for a number of Equine coat color, horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut (coat), chestnut will become palomino if they are heterozygous, having one co ...

, describes the process for horses by which the cremello, perlino, smoky cream double-dilute colors are created as well as the buckskin,

palomino Palomino is a equine coat color, genetic color in horses, consisting of a gold coat and white mane (horse), mane and tail; the degree of whiteness can vary from bright white to yellow. The palomino color derived from the breeding of Spanish hor ...

and smoky black single dilute colors. *

Dun gene The dun gene is a dilution gene that affects both red and black pigments in the equine coat color, coat color of a horse. The dun gene lightens most of the body while leaving the mane (horse), mane, tail, legs, and primitive markings the shade of ...

describes another common dilution gene in horses *

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 ...

, describes a different dilution gene in horses that also creates cream coloring, pale skin with mottling and light-colored eyes. * Pearl gene, also called the "Barlink factor", is a recessive gene. One copy of the allele has no effect on the coat color of black, bay or chestnut horses. Two copies on a chestnut horse produce a pale, uniform apricot color of body hair, mane and tail as well as pale skin. It also interacts with Cream dilution to produce "pseudo-double" Cream dilutes with pale skin and blue or green eyes. * Silver Dapple Gene lightens black hair, such as the mane and tail of a bay horse * Mushroom (horse) describes an unknown and unmapped theorized dilution gene dilutes red pigment in body color to a pale beige color.