Dilution gene

Tworats:left:agouti,right: coat lightened to blue by a dilution gene

Adilution geneis any one of a number ofgenesthat act to create a lighter coat color in living creatures. There are many examples of such genes:

General

Diluted coat colors havemelanocytes,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.

• Albinismdescribes a condition where pigment cells synthesize little or no pigment
• Leucismdescribes a condition that creates loss of pigment cells

Cats

Cat coat geneticsdiscusses many dilution genes incats.

Dogs

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

Appearance

Of the colour shades found in thecoat of dogs,the light brown caused bypheomelaninis hardly affected. Blackeumelaninis lightened to a grey called "blue". Chocolate brown eumelanine is lightened to the typical colour of theWeimaraner.

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  Great Daneslightened from black to blue by the dilute gene.
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  Doberman:black with tan in the back, blue with tan in the front. The light brown areas were hardly lightened at all
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  Blue-light brownbrindledog
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  For comparison without dilute gene: black-light brown brindle dog
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  Weimaraner
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  Silver Labrador
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  Colour dilution alopecia

Genetics

The dilute gene d is recessive to thewild typeallele D. A gene test can be used to determine a dog'sgenotypeconcerning genes for pigmentation. In somedog breedslightened by the dilute gene, the mutation d is associated withcolor 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.

Every dog has twoalleles- one from the sire and one from the dam. Thegene expressiondepends on thegenotype:

Heredity diagram
Left: black eumelanin, right: browneumelanin

1. DD: Both sire and dam have inherited the wild type allele. The coat is not lightened.
2. Dd: Either sire or dam have inherited theallelefor dilution. However, the dilution of colour is not visible in thephenotype- the dog has the same coat colour as a DD dog.
3. 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 theB locustake on the colour typical of the Weimaraner.

According to theMendelian Rules,an average of 25% of the puppies receive thehomozygousgene combination dd if both parents aregenetic carriers.

Horses

The effect of the champagne dilution gene on different horse coats.

• Equine coat color geneticsdiscusses color genes inhorses,including a brief description of dilution genes
• Equine coat colordescribes various colors in horses
• Cream gene,describes the process for horses by which the cremello, perlino, smoky cream double-dilute colors are created as well as thebuckskin,palominoand smoky black single dilute colors.
• Dun genedescribes another common dilution gene in horses
• Champagne gene,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 arecessive 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 Genelightens 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.

See also

• wikispecies:Felis sylvestris catus(cat)
• wikispecies:Equus caballus(horse)