Cream gene
Similarly, horses with a bay base coat and the cream gene will be buckskin or perlino.
The cream gene (CCr) is an incomplete dominant allele with a distinct dosage effect.
[3] Horses with two copies of the cream allele also exhibit specific traits: cream-colored coats, pale blue eyes, and rosy-pink skin.
Champagne (CH) dilutes are born with pumpkin-pink skin and blue eyes, which darken within days to amber, green or light brown, and their skin acquires a darker mottled complexion around the eyes, muzzle, and genitalia as the animal matures.
[3] The classic golden shade akin to that of a newly minted gold coin is common, but there are other variations: the darkest shades are called sooty palominos, unusual but most often seen in Morgans, can include a mane and tail with darker hairs and heavy dappling in the coat.
[5] The palest varieties can be nearly white, retaining darker skin and eyes, are sometimes mistakenly confused with cremello, and are called isabellas in some places.
The cream gene acting on a "blood bay" coat, the reddest shade, are pale gold with black points.
The cream gene acting on the darkest bays (sometimes mistaken for seal browns) may dilute to a sooty buckskin.
True seal brown buckskins can be very difficult to identify owing to their almost all-black coats.
Bleaching due to the elements means that the legs retain their color better, and can take on an appearance of having dark points like a bay horse.
When a horse is homozygous, meaning it has two copies of the cream allele, the strongest color dilution occurs.
True white horses have unpigmented skin and hair due to the incomplete migration of melanocytes from the neural crest during development.
This is also true of the normal variations in skin, hair and eye color encoded on the human SLC45A2 gene.
[9] True white coat coloring can be produced by at least half a dozen known genes, and some are associated with health defects.
[10] Another specific mutation on the endothelin receptor type B (EDNRB) gene is associated with the frame overo pattern produces Lethal white syndrome if homozygous, but carriers can be identified with a DNA test.
[20] The Andalusian horse has conflicting standards, with the cream gene being recognized by some registries,[20] but not explicitly mentioned by others.
Freckled skin and greenish eyes, or pedigree knowledge can yield clues, though the mystery can also be solved with a DNA test.
Some of the terms used to describe these combinations include: The cream locus is on exon 2 of the SLC45A2 gene; a single nucleotide polymorphism results in an aspartic acid-to-asparagine substitution (N153D).
[1] Mice affected by a condition homologous to cream exhibit irregularly shaped melanosomes, which are the organelles within melanocytes that directly produce pigment.
Therefore the skin, eyes, and hair of horses with the cream mutation do not lack melanocytes, melanosomes, or melanins, but rather exhibit hypomelanism.
Cream was first formally studied by Adalsteinsson in 1974, who reported that the inheritance of palomino and buckskin coat colors in Icelandic horses followed a "semi-dominant" or incomplete dominant model.
[26] There also were known health implications of albinism in humans,[27] and cultural prejudices; while a heroic figure such as Roy Rogers rode a golden palomino, the "Albino" in Mary O'Hara's Thunderhead portrayed a horse with a freakish defect.
The disparity in effects on red and black pigments is easy to identify in buckskins, with their black points, but it is also visible in CCr/CCr homozygotes: perlinos (homozygous cream on a bay coat) often retain points that are a darker shade of cream.
[1] A certain percentage of dark bay, seal brown, and black horses exhibit such subtle dilution of their coats as to be misregistered.
Horses sold after turning fully gray may surprise breeders by producing golden or cream offspring.
[9] A presumed knockout mutation in the same gene causes the phenotype of white tigers, which retain black striping though they lack the typical orange background pigmentation.
