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Color genes that
cause blue eyes:
The Cream dilution gene is an incomplete dominant, meaning that when a horse is homozygous for Cream (two Cream alleles are present, one from each parent) it looks different than when it is heterozygous (only one). All horses have a base color or red or black pigment and the black base may be modified by another gene called agouti and the horse will be bay. Cream modifies a horses base color. A horse with a red (Chestnut or Sorrel) base with one cream allele is a Palomino and a horse with a Bay base with one Cream allele is a Buckskin. One Cream allele does not dilute black pigment so that a buckskins legs remain black and black horse with one Cream allele is not diluted at all. The presence of the Cream allele can be confirmed by a test offered by some labs.
Two Cream alleles dilutes a horse to almost white with two blue eyes. The skin is pink and retains some pigment and may have some light freckling. White markings are faintly visible. Horses with two cream alleles are called Double Dilutes. When the base color is Chestnut they are called Cremellos, on a Bay base they are Perlino, and on Black they are sometimes called Smokey Cream although most are referred to and registered as Perlino.
Note: Double Dilute horses are sometimes called Albino. They are not true Albinos as seen in other species as the genetic control is different and they do retain some pigment. A true Albino always has pink or red eyes and although the reason is not known there has never been a true Albino horse recorded.
The inheritance of
Cream is as follows:
Dilute x Double Dilute =
Dilute x Palomino, Buckskin, or Smokey Black=
Dilute x Chestnut, Bay, or Black =
Palomino, Buckskin, or
Smokey Black x Palomino, Buckskin, or Smokey Black =
Palomino, Buckskin, or
Smokey Black x Chestnut, Bay, or Black=
Perlino. Ghost's Little BB (AQHA) of CW Warpaint Ranch.
The term Overo is used commonly to identify any pinto marked horse that is not Tobiano, however there are actually three genetically distinct patterns that are classified as Overo: Frame overo, Splashed White, and Sabino. Two of these (Frame Overo and Splashed White) cause blue eyes. I have discussed each pattern independently below.
The typical Frame Overo has white patches on the side of the body that do not cross the top line. The edges are jagged but not roaned. Frame causes face white varying in size from a star to a full bald face and one or two partial or full blue eyes. The legs are usually dark. The allele that causes the Frame pattern is dominant but lethal when homozygous. 25% of the foals from two Frame overo horses will be almost or completely white and will die soon after birth due to a defective colon. These foals are known as Lethal White Overos (LWO). Frame over has been observed to express very minimally as face white only or in some cases the Frame allele can be present without producing any discernable white. Frame has even been found in minimal form in some Quarter horses. There is a test for the gene that can be used to determine if a horse has the Frame allele so Frame to Frame crosses may be avoided. It cannot be stresses enough that any horse with a pinto pattern or of pinto ancestry should be tested before being bred. Solid horses, such as Quarter horses, should also be tested prior to breeding to a pinto or horse of pinto ancestry.
The inheritance of Frame Overo is as follows:
Frame Overo x Frame Overo = 25% will be Lethal Whites with two Frame alleles, 50% will have one Frame allele and possibly blue eyes, 25% will not have Frame.
Frame Overo x Non-Frame = 50% will have one Frame allele and possibly blue eyes, 50% will not have Frame.
Frame Overo Palomino. CF Blue Eyed Lullaby (American Paint Horse) of Chase-N-It farms.
Frame and Sabino. Lighten Up Bar (American Paint Horse) of CW Warpaint Ranch.
Splashed White makes a horse look like it was dipped in white paint. The markings are crisp and horizontal. It commonly has one or two partial or full blue eyes. Many Splashed whites are deaf and there may be a connection to the presence of white markings over or near the inner ear or the deafness may be a genetically linked trait. There has been very little research on Splashed White.
There are two theories about the genetics of splashed white. The first is that the Splash allele is Dominant and lethal when homozygous. The theory that it is lethal when homozygous is based on researchers having never found a Splashed White that produces 100% splashed white foals. However I believe the evidence at hand better supports the second theory.
The second theory is that it is an incomplete dominant so that like Cream the expressions are different depending on whether the horse has one or two Splash alleles. When the horse has one Splash allele it may have “normal” face and leg markings or may have a higher expression. The face markings are usually bottom heavy and may be a small snip or large blaze. The Splashed White blaze or bald face often runs off one side of the face. The leg markings tend to be clean cut at the edges and often the hind legs will have more white. Occasionally a minimally marked heterozygous splash will have one or two blue eyes. In fact one interesting expression of the pattern is blue eyes on a completely solid horse. This theory would account for most of the occasional blue eyes in solid quarter horses and other breeds.
When a horse inherits two Splashed White alleles the pattern is much louder. The face is usually bald and the white occasionally covers even the ears. There may be large belly spots and the leg markings extend up onto the body. The white may even cross the top line. Blue eyes and white on the bottom of the tail usually accompany this expression. Blue eyes are common with both homozygous and heterozygous Splash horses. Splash also appears to be enhanced by the presence of Sabino.
If the incomplete dominance theory is correct it would explain how splashed whites such as Gambling Man and Gunner could be produced from two normally marked Quarter horses. The Mr. Gunsmoke line is particularly prone to cropout Splashed whites. It would also explain the apparent lack of homozygous Splash individuals. The homozygous horse would pass on one copy of the allele 100% of the time but the heterozygous Splash foals would often be minimally marked and registered as solid. In order for the horse to produce a foal similarly marked to himself the other parent needs to also have at least one splash allele to pass on.
The inheritance of Splashed White according to the incomplete dominance theory is as follows (these calculations do not take into account the effects of other white marking producing genes):
Homozygous Splash + Homozygous Splash = 100% Homozygous Splash foals, loudly marked often with blue eyes.
Homozygous Splash + Heterozygous Splash (may or may not be considered "pinto") = 50% Homozygous Splash foals, 50% Heterozygous Splash foals.
Homozygous Splash + Non-Splash = 100% Heterozygous foals, occasional blue eyes.
Heterozygous + Heterozygous =25% Homozygous foals, 50% Heterozygous foals, 25% Non-Splash foals.
Heterozygous + Non-Splash = 50% Heterozygous Splash foals, 50% Non-Splash foals
Splashed White. Duke (MFT) owned by Wendy Normand.
Champagne is a newly recognized dilution gene. It is a simple dominant and dilutes both red and black pigment. A champagne will always have at least one champagne parent. On a Chestnut base it is called Gold Champagne, on bay it is Amber Champagne, and on Black it is Classic Champagne. The Champagne gene dilutes the skin to pink that later turns purplish and may have freckles. The eyes of the Champagne are born blue but change to amber.
Gold Champagne heterozygous Splashed White. Sonny (MFT) owned by Wendy Normand.
"Blue Eye Gene":
Some people think that there may be a blue eye gene independent of any pinto pattern. At present there is no evidence to prove or disprove this theory. In my opinion all spontaneous blue eyed are causes by one of the above genes and most often by Splash. The occasional blue eye in purebred Arabians was attributed to this blue eye gene but recently it has been discovered that Splashed White does indeed occur in the breed and may be the cause of the blue eyes.
similar colors that do not cause blue eyes:
The Dun dilution gene produces a color on a bay horse that is easily confused
with Buckskin. The major physical difference is the presence of a dorsal stripe,
shoulder bars, face mask, and leg bars on the dun horse. A Buckskin will
sometimes exhibit such markings but they are usually indistinct and are caused
by a modifier gene called Sooty or Smutty. The Sooty gene adds dark hairs to the
coat and sometimes the dark hairs produce dapples or a dorsal stripe known as
countershading. The Dun allele dilutes both red and black pigment to produce Red
Dun on Chestnut base, Bay or Yellow Dun on Bay base, and Grullo on Black base. The gene,
unlike cream, is a simple dominant. A homozygous dun horse will have 100% dun
foals and look exactly the same as a horse with only one dun allele. If a horse cannot be
visually identified as either Dun or Buckskin the parentage must be considered.
A Buckskin will always have a Buckskin, Palomino, Smoky Black or Double Dilute
parent, and a Dun will always have a Dun, Red Dun or Grullo parent. A horse may
have both cream and dun. A horse with Cream and Dun on a Chestnut base is called
a Dunalino and on a Bay base it is called Dunskin. A horse can
also be tested for Cream gene but no test is available for Dun.
Sooty Buckskin with countershading. Carmelita (Quarter Horse cross) of Danger Ranch.
Sabino does not cause blue eyes but sometimes resembles Frame Overo or Splashed White. Sabino expression can be highly variable from the minimal of a very small amount of "normal” white markings to an all white horse with dark eyes. Common features are white on the legs and face (particularly the chin), roaning, jagged roan edged belly and body spots. The exact genetic control of Sabino is unknown but one theory is that it is controlled by many genes that combine in different ways to form the various expressions of Sabino. This theory would help explain some cropouts where normally marked horses with no pinto ancestry produce loudly spotted or even white Sabino foals.
A maximum Sabino is completely white with dark eyes and can be confused with a Double Dilute. The horse is literally one big white spot. If there is also Frame Overo or Splashed White present the eyes may be blue causing further confusion. The skin of the maximum white pinto is completely devoid of pigment and will sunburn unlike a Double Dilute. A Cream gene test or studying the parentage will determine the genetic makeup of the white horse. A blue eyed white horse can also be produced by Frame and/or Splash combining with Tobiano.
Medium Sabino Palomino. May also have frame. Note pointy stockings, jagged edges, and roaning. Alchemette (Arab cross) of Danger Ranch.
The colors that have blue eyes are Double Dilutes, Splashed Whites, Frame Overos, and some Champagnes. Tobianos, Sabinos, Duns and solids do not have blue eyes unless the horse also has one of these patterns or dilutions.
Note: If you would like me to use photos of your horses please email them to me at firstname.lastname@example.org. Please only send good, clear photos and title your email appropriately. I would like pictures of any dilutes and paint patterns with and without blue eyes.
This page will continue to be updated as I become aware of new or corrected information.
Update: I am currently rather busy and will not be updating the pictures for a few weeks or months. Thank you for reading!