Dominant White

Dominant White

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The hunter mare pictured above appeared in Farm Livestock of Great Britain (R. Wallace, 1907). The caption notes that her white foal was sired by a dark chestnut stallion. The tendency of white-born horses to produce their own color 50% of the time lead early researchers to call the color “dominant white.”
Although the situation with this group of patterns – both in terms of inheritance and phenotype – is more complex than early geneticists expected, the name they coined is still used. Here is a partial list of instances where it has been used in peer-reviewed publications in the past three years.

To date 22 different alleles ( W1–W19 , W21–W24 ) underlying dominant white phenotypes have been identified.

This Belgian sample set showed genotypic variation in coat colour loci for agouti, dominant white 20 and dun.

To date, 58 variants affecting pigmentation have been described, including 27 in the KIT gene that contribute to the dominant white phenotype.

The term has been used by researchers in recent articles in non-technical publications as well. It has not, as is sometimes asserted, been retired. Because it does have a long history of use when talking about white (and mostly-white) horses, and because it is widely used in other species, it is unlikely that it will disappear any time soon. I tend to use sabino as my umbrella term for this group of patterns, but others use dominant white or even both terms.
Lesli Kathman
Equine Tapestry is a blog focused on the coat color genetics in horses, with occasional detours into breed history, genetic preservation and other domestic animals.
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The genetic sequence for Dominant White, Dun and Smoky are as follows:
“Sequence analysis showed that the Dominant White allele was exclusively associated with a 9-bp insertion in exon 10, leading to an insertion of three amino acids in the PMEL17 transmembrane region. Similarly, a deletion of five amino acids in the transmembrane region occurs in the protein encoded by Dun. The Smoky allele shared the 9-bp insertion in exon 10 with Dominant white, as expected from its origin, but also had a deletion of 12 nucleotides in exon 6, eliminating four amino acids from the mature protein.”
Some poultry fanciers may also be familiar with the currently unapproved breed historically known as “Erminette,” whose plumage color is created from the a copy of the Dominant White gene on Extended Black. F.B. Hutt completed a study on the Erminette breed and found that a typical Erminette is heterozygous for a gene and tentatively assigned the gene name as Er. When the birds in his study were mated together, solid white, black flecked phenotype, and solid black offspring were produced. He eluded to the gene being like Dominant White in his study. Subsequent analysis has revealed that the gene which creates the plumage color for the Erminette breed is Dominant White (I).

I am originally from Alabama. I attended Freed-Hardeman University. I graduated with a double major in Psychology and Kinesiology. I worked as a family counselor for several years prior to becoming a stay at home mother. My husband and I have four children and we reside in Lawrence County, TN. I enjoy studying poultry genetics and raise standard-bred Ameraucana.

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Several scientific studies completed in the early 1900s, including those by Bateson (1902), Hurst (1905), and Hadley (1913), found that the white Leghorn carries an autosomal gene capable of inhibiting the development of black pigment in plumage. Hadley (1913) designated this gene as “I” (inhibitor of black pigment), otherwise known as the Dominant White gene. When white Leghorns were crossed with breeds that have solid black plumage, the offspring produced were predominantly white.
Hadley found that in this instance, the genes necessary for black pigment are present but do not manifest themselves due to the inhibiting action of the gene. Pigment is formed by melanocytes in feather producing cells, but there is a nontransfer of pigment by melanocytes to keratinoblasts.
Dominant White, Dun, and Smoky are alleles at the Dominant White locus. Dominant White and Dun inhibit the expression of black eumelanin. Analysis has revealed that Dominant White, Dun, and Smoky occur due to mutations of the PMEL17 (premelanosomal protein) gene. These are the only PMEL17 mutations that have been found to have a phenotypic effect in poultry.
Modifying genes, which limit or expand the amount of black on a heterozygote, affect the overall number of black feathers present on the plumage. The modifying genes also affect whether the black plumage feathers will be solid black and the white plumage feathers solid white.
Bateson, W., 1902. Reports to the Evolution Committee of the Royal Society. London, Harrison, 160pp.
Hadley, 1913. Studies on the inheritance of poultry. I, The constitution of the White Leghorn breed. Rhode Island Agric. Exp. Sta., Bull. 155: 151-216. Plates I-IIL
Hurst, C . C , 1905. Reports to the Evolution Committee of the Royal Society. Report II. Experiments with poultry, pp. 131-154.
Kerje, S. The Dominant White, Dun and Smoky Color Variants in Chicken Are Associated With Insertion/Deletion Polymorphisms in the PMEL17 Gene Sequence, Genetics, Volume 168, Issue 3, 1 November 2004, Pages 1507–1518, https://doi.org/10.1534/genetics.104.027995
Kimball, E. On the Nature of White Plumage, Poultry Science, Volume 37, Issue 3, 1958, Pages 730-731, ISSN 0032-5791, https://doi.org/10.3382/ps.0370730 . ( https://www.sciencedirect.com/science/article/pii/S0032579119576374 )
Lippincott, W. The Hereditary Relation of Dominant White and Blue in Chickens. Poultry Science, Volume 2, Issue 5, 1923, Pages 141-145, ISSN 0032-5791, https://doi.org/10.3382/ps.0020141 . ( https://www.sciencedirect.com/science/article/pii/S0032579119567670 )
Sato, S. Mapping of the Recessive White Locus and Analysis of the Tyrosinase Gene in Chickens, Poultry Science, Volume 86, Issue 10, 2007, Pages 2126-2133, ISSN 0032-5791, https://doi.org/10.1093/ps/86.10.2126 . ( https://www.sciencedirect.com/science/article/pii/S0032579119392430 )
Smith, L.T. On the Allelism of Blue Plumage and Dominant White, Poultry Science, Volume 48, Issue 1, 1969, Pages 346-347, ISSN 0032-5791, https://doi.org/10.3382/ps.0480346. ( https://www.sciencedirect.com/science/article/pii/S0032579119528899 )
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White horses have a special meaning in mythology (Pegasus and Unicorn) and different cultures worldwide (representing wisdom, power, fertility, or even death). But what is a true white horse?
A Dominant white horse also called “white” or “spotted white,” has a white pattern produced by mutations of the KIT gene (W1,W2,…). It’s characterized by white spotting. However, the extent of white is highly variable, ranging from only white spots on the face and legs to completely white. The eyes are usually brown but can occasionally be blue.
There are many different mutations of the kit gene for dominant white , W1, W2, W3,… .
Until now 30 different alleles have been discovered ( source ).
The Dominant White pattern can occur with any base coat color (black, chestnut, bay ) or diluted coat color ( dun , cream , silver , or champagne ).
It can also exist in conjunction with other white patterns ( Frame , Sabino , Tobiano , Splashed White , Leopard Complex , or Roan ).
The term dominant white is misleading because it leads to the belief that these mutations will produce completely white horses. However, this is not always the case.
Dominant white (W) patterns can vary greatly in the extension of white on the coat. They can range from a completely white coat to only white markings on the face and legs.
We can group dominant white horses into three different categories:
These horses are seen as colored horses with common white markings. similar to Splashed White (W20 produces this coat)
These horses are commonly confused with Sabinos . (W5, W15, W19 produce this pattern)
These horses are either: – completely white (consistently produced by W2) – Nearly complete white with minimal colored spots, mainly in the ears and topline (seen with W3)
This grouping is just to give an idea of the range of white area that can exist for different Dominant white expressions, but the borders between categories can be quite fuzzy.
Additionally, the variability increases enormously when the 2 alleles (one from each parent) have different combinations. Let’s consider, for example, the W20 allele.
The letter W has been used for a long time to represent Dominant White in horses. We will use w (little w) to represent the recessive allele. All non-white horses are ww.
As the name suggests, the Dominant White allele is a dominant allele, which means that only one copy of the allele is needed to express the Dominant White traits. Both homozygous ( W/W ) and heterozygous ( W/w ) horses exhibit the same phenotype.
The Dominant White mutations are located on the KIT gene.
The KIT gene in horses is responsible for many different white patterns. These white patterns can be grouped into four different allele types: sabino(SB1), tobiano(TO), roan(RN) , and dominant white(W)
Sabino 1 was identified in 2005. The researchers named this allele Sabino 1 because they thought they would find more alleles and would then name them Sabino2, Sabino3, etc.
However, the next allele that was found on the KIT gene caused a dominant white trait. So the allele was named W1. The following alleles found on the KIT gene also produced the dominant white trait, and so they were named W2, W3, … and so on.
After that, the following alleles discovered on the KIT gene were given a name on the W series, even those with sabino-like patterns. Perhaps some of these alleles should have been named sabino instead of white.
So most probably, the Sabino 2 will never be named, and if more sabino-like alleles are found, they will likely be designated within the W series.
In any case, all these alleles are versions of the same KIT gene.
Because all the alleles, W1, W2, W3,….., SB1, TO, and RN are on the same gene (KIT), only two of them can be present in a horse (one from the sire and another from the dam).
So, for example, we can have genotypes with only dominant white alleles like W20/W20 or W20/W22 or genotypes that cross different white patterns on the KIT gene, like, for example, W20/TO, W20/SB1, or W20/RN .
This also means that if a horse has two KIT gene patterns (ex: W20/TO), it will pass one or the other to its offspring but never both.
Horses can carry two KIT gene mutations, ex: W1/TO, and an additional splashed white (SW) plus a Frame Overo (O) because different genes create these different white patterns.
These successive additions, acting together in a cumulative way, can create coat colors that make it impossible to visually detect the genes behind it. In these cases, it is necessary to perform a DNA test.
Dominant white has appeared, although rarely, among some breeds of horses.
The table below shows which alleles have been found in the different breeds.
Considering the high diversity of mutations that have been found so far in the KIT gene, it is likely that new alleles of the W series can appear in any breed of horse.
As with any depigmented horse, dominant white horses will be extra sensitive to sun exposure, due to the lack of protective pigment.
The pink skin of white horses does not have melanin and therefore is not protected when it is exposed to sunlight. This leaves the skin at the mercy of UV rays and vulnerable to damage.
This is not simply a sunburn, it may cause skin lesions. These lesions present redness, swelling, and itching. Subsequent infections may occur, followed by necrosis and shedding of skin. Cancer of the skin may also develop.
You may want to try the Summer Care Butter to protect your horse´s skin from sunburn. This product can be purchased at Amazon.
Most famous white horses are actually greys with hair coats turned to fully white.
However, the horse “Silver”, ridden by the Lone Ranger, was a true white horse.
Another famous truly white horse is Yukichan, a Japanese Thoroughbred racehorse.
Grey horses and cream horses (Cremello and Perlino) are often called white because the hair appears to be white, but these are not true white horses. The true white horses are produced by White Pattern genes.
In this comparison, we are considering dominant white horses that have completely white coats.
Grey Horses are often confused with true white horses, however, it is quite easy to differentiate them.
A double dilute cream horse such as Perlino and Cremello will appear white, but there are some subtle differences when compared to a true white horse.
If you would like to learn more about horse colors and white patterns, you may want to read the following books, available on amazon.
The links below that lead to products on Amazon are affiliate links and I earn a commission (with no additional cost for you) if you make a purchase.
The following books are an introduction to horse colors and white patterns which are full of images and very easy to understand.
A more technical book about horse colors, but still very easy to understand.
Equine Color Genetics 4th Edition by D- Philip Sponenberg
Franches-Montagnes . Horses trace back to Cigale, a mare born in 1957.
Thoroughbred. Horses trace back to KY Colonel, a chestnut with extensive markings born in 1946
Arabian. Horses trace back to R Khasper, near white stallion born in 1996
Mostly white. Horses homozygous W3/W3 are likely embryonic lethal
Camarillo White Horse . The Camarillo White Horse is a rare horse breed less than 100 years old known for its pure white color. It started in 1912 with the stallion named Sultan.
Completely white or mostly white with colored markings that fade with time
Thoroughbred . Horses trace back to Puchilingui, a stallion born in 1984.
The phenotype varies from Sabino-like pattern to completely white Horses homozygous W5/W5 are likely embryonic lethal, but this still needs to be confirmed.
Thoroughbred . Only identified in a single white horse born in 2004
Thoroughbred . Identified in a partially white filly
Icelandic Horse. Identified in a partially white horse.
Holsteiner. Identified in a completely white horse born in 2006
Quarter horse . Horses trace back to GQ Santana born in 2000
The phenotype varies from Sabino-like pattern to completely white
German Draft . Identified in a complete white stallion born in 1997 and three white offspring
Thoroughbred . Identified in a single colt born and died in 2010
Quarter horse and Peruvian Paso. Identified in a crossbred family with two white animals. Founder is unknown
Thoroughbred. The founder is suspected to be Shirayukihime, born in 1996.
Arabian. The founder is Khartoon Klassic born in 1996
Heterozygous partially white, and homozygous are completely white.
Oldenburg. Identified in a family with three almost complete white horses. the founder is suspected to be Celene born in 2003
Japanese draft. Identified in a horse born in 2010
Completely white with one blue eye and one brown eye
Swiss Warmblood . Identified in a single white horse with extended white speckled areas.
Part-Bred Arabian: The founder is suspected to be Fantasia Vu, born in 1990
Bald faces extended white legs and irregular belly spots
Very common mutation. Is thought to be a white booster. W20 on its own causes markings on the face and legs, and small belly spots. When combined with other mutations from KIT gene, W20 greatly increases the white area.
Icelandic Horse. Identified in a single horse with a sabino-like pattern.
Many breeds Thought to have originated in Thoroughbred mare called Not Quite White, born in 1989.
Sabino-like to completely white. W22 is sabino-like, but when combined with W20, is completely white
Arabian Founder born in 1989. but line appears to have died out
Italian Trotter Via Lattea, born in 2014
Australian Thoroughbred . Originated in a mare called Laughyoumay, born in 2001
Australian Thoroughbred Originated in a mare called Marbrowell, born in 1997
Australian Thoroughbred Originated in a mare called Milady Fair, born in 1960. Most horses with this mutation are descended from her great-grand-colt, Colorful Gambler.
Berber . Identified on Aghilasse and his son Kairaan

Last Updated on February 1, 2022 by admin
Go to any racecourse or racing stables and you will see that Thoroughbreds are mostly black , bay, chestnut, or brown. You might occasionally see a gray Thoroughbred, but overall the coloring of this breed is fairly basic. But did you know that you can get a dominant white Thoroughbred horse as well?!
The science behind horse coloring is very complex, and to understand how we get a white horse we need to know a bit more about the basic horse color genes. Let’s find out more about dominant white Thoroughbred horses!
However, when it comes to Thoroughbreds, they come in just 8 different colors! These are:
Of these colors, some are much more prevalent than others. Bay, chestnut, and gray are the most common colors of Thoroughbred, while it is less likely that you will see a black, palomino, or roan Thoroughbred horse. White Thoroughbred horses are the rarest of all the colors.
Interestingly, all horses are based on two basic colors – black and red (chestnut). Each horse inherits either a black or red gene from each parent, which determines the basic coat color. Two black genes will create a black horse, two red genes give us a chestnut, and one of each results in a bay horse.
So, if a horse has only these basic genes, its color will be black, bay, or chestnut. It is only when the parents also carry other color-changing genes that we start to see different colors and markings emerging.
For example, some horses carry color dilution genes. These have the effect of lightening the pigment of the base coat color, and they all act in different ways. For a Thoroughbred to be palomino colored, it will need to inherit the cream dilution gene from one of its parents.
Gray coat coloring occurs when a horse inherits the gray gene from one or both of its parents. This is a dominant gene, that overrules all other color influencing genes. However, gray horses are not born this way – as a foal, they will have their basic coloring, which will fade to gray over time.
A dominant white Thoroughbred horse is one that has inherited a specific gene from one or both parents that creates white coloring. In a white horse, the skin will appear pink, as it has no pigmentation. The eyes of a white horse are usually dark, unlike other similar coat colorings.
A horse that has dominant white genes may be white all over its body, or it can have patches of darker hair that reflect the base coat color and any other color-changing genes. The skin under this dark hair will also be white.
A white Thoroughbred foal is so rare that the birth of one will often make the headlines! These bloodlines are very rare, but fans of this color are beginning to understand how to breed more white horses of this breed. So, in the future, we might see many more winning Thoroughbred horses on the race track!
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