A dilution gene is any one of a number of

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

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

General

Diluted coat colors have melanocytes, 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 describes a condition where pigment cells synthesize little or no pigment * Leucism describes a condition that creates loss of pigment cells

Cats

* Cat coat genetics discusses many dilution genes in cats

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 (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the am ...

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

Weimaraner The Weimaraner ( ) is a large dog that was originally bred as a hunting dog in the early 19th century. Early Weimaraners were used by royalty for hunting large game such as boar, bear and deer. As the popularity of large game hunting began t ...

. Dangerousdream.jpg, Great Danes 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 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 Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...

Labrador-Weimaraner-Nachkomme mit Farbmutanten-Alopezie.jpg, Colour dilution alopecia

Genetics

The dilute gene d is recessive to the wild type allele D. A gene test can be used to determine a dog's genotype concerning genes for pigmentation. In some dog breeds 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 (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chrom ...

s - one from the sire and one from the dam. The gene expression depends on the genotype: Dilution Gene - inheritance and effect

# 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 (biology), morphology or physical form and structure, its Developmental biology, developmental proc ...

- 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. Mo ...

gene combination dd if both parents are genetic carriers.

Horses

* Equine coat color genetics 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 million yea ...

s, including a brief description of dilution genes * Equine coat color describes various colors in horses *

Cream gene 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 ...

, 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 genetic color in horses, consisting of a gold coat and white mane and tail; the degree of whiteness can vary from bright white to yellow. Genetically, the palomino color is created by a single allele of a dilution gene called t ...

and smoky black single dilute colors. * Dun gene describes another common dilution gene in horses * Champagne gene, describes a different and rarer 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 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 ...

, describes a dilution gene that works in a unique manner, lighting the mane and tail of a horse to a greater degree than the body color (opposite of most dilution genes, which act more strongly on the body color) * White (horse) describes several unique genetic processes that create truly white, not diluted, color in horses. * Gray (horse) explains the process of the gray gene, which lightens the coat over time, but is not a dilution gene. * Mushroom (horse) describes an unknown and unmapped theorized dilution gene dilutes red pigment in body color to a pale beige color.