Cream gene

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Cream gene

The cream gene is a dilution gene expressed in horses, and produces lighter colors. When one copy of the gene is present, it dilutes "red" color (chestnut) to yellow or gold, and red manes to white, but does not dilute black color at all. When two copies of the gene are present, both red and black hairs become a paler color; red hairs still become cream, and black hairs become reddish.

Cream horses are not "white" horses. Dilution coloring is not related to frame overcoat patterns or lethal white syndrome, nor is cream related to the controversial "white" or "dominant white" (W) gene; it does not produce white horses.

Colors produced by the cream gene

The cream gene produces the colors:

What it does

The cream gene is an "incomplete dominant" gene, which means that it is expressed to some degree even when there is only one copy of the gene--it is dominant--but it expresses itself even more when there are two copies (one from each parent).

Coat color: The cream gene lightens the base coat. One copy lightens red (chestnut) coloring to pale yellow or gold, such as palomino, but does not overtly affect black color. Two copies will lighten both red and black hairs.

Eye color: double dilutes have blue eyes (unlike brown eyes of a gray and some white horses). Depending on the genes carried by the other parent, a single dilute, such as a Palomino, can be born with bluish brown eyes and pinkish skin that darkens after birth, or may be born with dark eyes and skin.

Single dilutes

Single dilutes receive the cream dilution gene from only one parent. The other parent does not carry the dilution gene.

Palomino: One parent genetically contributes the cream gene, and both parents contribute a "red" base coat gene. The cream gene lightens the coat to pale yellow/ gold and the mane to white, producing a palomino.

Buckskin: One parent genetically contributes the cream gene, and one or both passes on the genes for bay (the black base gene and the agouti gene that restricts the black to the points only. (see bay) for explanation of the agouti gene). The single copy of the cream gene lightens the coat to pale yellow, but cannot change black, leaving the mane, tail, and lower legs black.

Smoky black: A single copy of the dilution gene is added to the gene for a black base color. One cream gene cannot change the color of black hairs, so the horse looks black, "masking" the cream gene. Although the gene is masked, it can be passed on. Thus a smoky black may sometimes produce, for example, a buckskin or palomino horse when crossed on a bay or chestnut, even though neither parent appears to have the gene. Smoky black only occurs to genetically black horses. Bays and chestnuts, no matter how dark their base coat, will have red hairs diluted to gold.

Double dilutes

Double dilutes have 2 cream genes (one from each parent). This even further lightens the red color: from the golden color of one dilute to a pale cream color of the double dilute. It also results in lightening of black hairs to a reddish color.

Double dilutes are not true white horses, nor are they albinos, even though they have pink skin. There are no true albinos in the horse world.

Nor are double-dilutes gray: they have blue eyes and pink skin, whereas a gray horse has dark eyes and black skin.

Cremello: The double dilution of chestnut/red coats. The body and mane is a cream color (hence the "cream gene").

Perlino: Double dilution of bay, so that the body is a light cream, with reddish points (mane, tail, lower legs).

Cremello and Perlino horses sometimes fade in color as they mature, so that they look almost white. Their eyes and skin remain unchanged.

Smoky cream: Double dilution on a black coat. The cream gene is not completely hidden as it is in the smoky black. The horse becomes a light gold or cream color which can be difficult to tell from a cremello or perlino (although colors vary). If one wants to be sure of the base color, the horse can be tested for the presence of the Agouti and Extension genes.

Color differences

Color	Coat Color (Birth)	Coat Color (Adult)	Eye Color	Skin Color
Gray	Bay, chestnut or black	Grays until White	Brown	Black
Cremello	Light Cream, visible markings	May fade to near-white	Blue	Pink
Perlino	Light Cream, visible markings, mane and tail reddish	May fade to near-white	Blue	Pink
Palomino	Light Gold or Cream, visible markings	Usually does not lighten with age	Dark, amber or brown (absent other dilution genes)	Black, except under white markings
Buckskin	Light Gold or Cream, visible markings, mane, tail, forelock and legs black	Usually does not lighten with age	Dark, amber or brown	Black, except under white markings
White	White (is not born dark)	White	Depending on genetic mechanism at work, Blue or Dark	Pink

Other dilution genes in horses

There are three other dilution genes in horses, each producing different effects than does cream:

Dun color is produced by a separate dun gene that acts upon a base coat color to produce a different form of color dilution, along with distinctive "primitive" markings that include a dorsal stripe, horizontal leg striping, and usually a duller shade of dilution than cream; classic dun are more tan than gold. It is also a simple dominant, not an incomplete dominant.
The Champagne gene produces a dilution that strongly resembles cream. However horses with Champagne are born a different color than they mature, usually have amber or green eyes in adulthood and usually have mottled skin.
The Silver dapple dilution acts only on a black coat, lightening the body coat to a chocolate brown and the mane to a lighter shade of flaxen or silver. It can be carried by non-black horses, but will not manifest absent black coloring. It has no impact on skin color or eye shade.
The Pearl gene dilution, also called the "Barlink factor," is a recessive gene that can interact with Cream dilution to produce "pseudo-double" Cream dilution with pale skin and blue or green eyes.

Other terminology

This dilution gene is sometimes also called the "creme" gene. However the spelling most often used by geneticists, is "cream." "Creme" is actually an abbreviated form of "cremello", which refers specifically two cream genes on a chestnut base.

References

"Horse coat color tests" from the UC Davis Veterinary Genetics Lab
"Introduction to Coat Color Genetics" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008