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 cream gene (CCr) is an incomplete dominant allele with a distinct dosage effect. The DNA sequence responsible for the cream colors is the cream allele, which is at a specific locus on the MATP gene. Its general effect is to lighten the coat, skin and eye colors. When one copy of the allele is present, it dilutes "red" pigment to yellow or gold, with a stronger effect on the mane and tail, but does not dilute black color to any significant degree. When two copies of the allele are present, both red and black pigments are affected; red hairs still become cream, and black hairs become reddish. A single copy of the allele has minimal impact on eye color, but when two copies are present, a horse will be blue-eyed in addition to a light coat color.
The cream gene is one of several hypomelanism or dilution genes identified in horses. Therefore, it is not always possible to tell by color alone whether the CCr allele is present without a DNA test. Other dilution genes that may mimic some of the effects of the cream gene in either single or double copies include the pearl gene, silver dapple gene, and the champagne gene. Horses with the dun gene also may mimic a single copy of the cream gene. To complicate matters further, it is possible for a horse to carry more than one type of dilution gene, sometimes giving rise to coloring that researchers call a pseudo double dilute.
The discovery of the cream gene had a significant effect on breeding, allowing homozygous blue-eyed creams to be recognized by many breed registries that had previously registered palominos but banned cremellos, under the mistaken notion that homozygous cream was a form of Albinism.
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