Colour Genetics
 

 

Home

News

The stud

Results

Stallions

Mares

Foals

Young Stock

Services

Sale

Sold

In memorium

Colour Genetics

Gallery

Contact

Links

 

 

 

 

 

 

 

 

 

 

 

On this page I will try to explain a little bit about colour genetics and colours.

____________________________________________________________________________________________________

Shatland Ponies and Colours.

The shetland pony is a very interesting breed when it comes to colour and colour breeding.. They exist in a a lot of different colours and colour combinations. Only the spotted colour is not allowed in shetland ponies..
Even though the shetland pony is a breed with many interesting colours, there seems to be very little knowledge about about colour genetics within the different breed clubs, and among many breeders. For instance I often come across ponies with the wrong colour listed in their papers.
I therefore hope that this review of colours and their inherritance patterns, will be a help to those, who like myself, are interested in breeding shetland ponies with specific colours.
If you have any questions or suggestions, corrections or anything like that, please contact me and I'll look into it.. The same goes if you have any direct questions about your own breeding.. I willl do my best to help, and I am allways up for a talk about colours..

Base coat colours

The horse has three base coat colours: black, chestnut and brown/bay. These colours stem from a pigment, formed by the melanocytes, called melanin. The melanocytes can make to different kinds of pigment. The black pigment eumelanin (which gives rise to black horses) and the red pigment phaeomelanin (which gives rise to chestnut horses). The brown or bay horses happens when the hairs are coloured alternately with both eumelanin and phaeomelanin. Wheter the horses melanocytes form eumelanin, pheaomelanin or a mixture og the two, is decided by the horses genes. Besides the three base coat colours there is a large number of other colours, which are all modifications of the three base coat colours, and they have all arisen from mutations in the horses colour coding genes.

The Genes

The three base coat colours are controlled by 2 genes or so called loci. A locus is a specific place on the chromosome. Genes that have the same locus are called alleles. Each locus has at least 2 alleles. The 2 series of alleles controlling the base coat colours are::

A-series: Consist of 4 alleles, that determine the base coat colurs pigment pattern. Meaning the distribution of eumelanin or phaeomelanin on the horses body. Agouti means striped, and here the hair changes colours from root to tip. Phaomelanin is present at the root and eumelanin is present at the tip of the hair.
A+: Agouti wildtype. Eumelanin is restricted to the pasterns and possibly the front knees and the hocks. The mane and tail are also eumelanic (meaning black).
A: Agouti. As above, but here the eumalanin is destributed further up the legs.
at: Tan points or eumelanic and tan: Results in eumelanin on most of the body, or a mixture of eumelanic og phaeomelanic hairs, with strictly phaeomelanoc hairs on smaller areas (for instance behind the ears, on the flanks and on the insides og the thighs). Mane and tail are eumelanic (black)
a: Non-agouti. Results in an evenly coloured horse with eumelanin across the entire body..

E-series: Consist of 3 alleles that determine the distribution of eumelanin.
ED: Results in a dominant distribution of eumelanin meaning meaning plain eumelanic.
E: Results in a normal distribution of eumelanin, allowing eumalnin on the areas determined by the allels of the A locus.
e: Restricst eumalnin, giving rise to at distribution of phaeomelanin to the entire body. The effect og the A locus is hereby annuled.

(The dominant genes are designated with an upper case letter and the recessive genes are designated with a lower case letter)

The horse allways receives/inherits 2 alleles in each locus. 1 from the stallion and 1 from the mare. When a gene is dominant, it only needs 1 allele of the gene, for the colour to show though. If the gene is recessive, it needs to ocupy both alleles in the locus for the colour to show though.. When a colour shows through (meaning you can see the colour on the horse) then you talk about the horse's phenotype. The colours the horse is carrying, but which doesn't show through, is a part of the horse's genotype. When a horse has 2 alleles of the same gene (for instance: ee) it is said that the horse i homozygous for that particular gene. If the horse has 2 different alleles af a gene (for instance: Ee) then the horse is heterozygous for that gene.

Brown/bay horses
The brown or bay colour is actually a modification of the black base coat colours. This is also why some people don't count brown or bay as one of the base coat colours. It has a dominant inherritance patterns, meaning that only one allele of the gene is necessary for the colour to show through. The colour will need the horse to carry at least one allele for black, to be able to show through.
The genotype A_ B_ E_ ( _ meaning it kan be either the dominant or the recessive allele) results in a light brown horse with black legs, mane and tale.
If the horse has A+ instead of A, then the black on the legs, is restricted to the pasterns and possibly the front knee and the hocks.
If the horse allso has a gene called ”sooty” (the Sty gene), then you will have a darker, almost chetnut brown horse, that diffuses to almost black in the head and on the back. In english this colour is called ”bay” (red bay, blood bay, mahogany bay og dark bay)
The genotype: at_ B_ E_ results in a dark brown horse with tan points behind the ears, on the flanks and inner thighs. (mostly spots where the horse's skin is paticularly thin). The hairs consists of a mixture og black and red hairs, and the colour is darkest along the back. The longhairs (mane and tail) are still completely black. In english this colour is called ”brown” If the horse also has a sooty factor (Sty) you gat a black brown horse that is practically completely black, but with a hint of red-brown areas in the afore mentioned thin skinned spots.
In english the colour is called: ”black-brown”

(Zonneroosje v.d. Uilecotenweg - Bay - Stutteri Bakkegaard)

Red/chestnut horses
The red horses are probably the hardest to genotype. there are so many different shades of red, that it is almost impossible to keep track of. Here are some examples.
The genotype ee will always result in a chestnut horse, no matter the genes in the A and B series, and the genotype bb allways results in a chestnut horse, no matter the genes in the A and E series.
The genotype A_ bb E_ results in a chestnut horse whith brown legs, mane and tail..
The genotype aa bb ED_ resilts in a dark chetnut horse.
The genotype: at_ bb E_ results in a dark chestnut horse, with brown pigment on most of the body and red pigment on smaller areas.
The genotype: ee A+_ results in a very light chetnut, like the the colour seen in the haflinger horse.
Both the genotype: ee AA and the genotype: ee At_ results in a red horse (Red chestnut, where the coat shines red, and standard chestnut, where the coat shines yellow)
The genotype: ee aa results in a dark red horse (Liver chestnut)
Mulberry (in english) or sorrel (in american) is the designation for a red horse with a light (flaxen) mane and tail. More on this gene further down the page.
Pigment density and sooty factor can also influence the red nuance in the chetnut horses.

The red colour has a recessive inherritance pattern, which means that two red horses, can only have red offsoring, becuse they are bot homozygous for the red gene (ee). Two black horses will be able to produce a red foal, bacause they can both be carriers of red (Ee). Both parents have to carry the recessive allele for red, for the foal to be red, because the foal has to inherit 1 red allele from each parent.

(Bakkegaard's Tinylightning - Chestnut - Stutteri Bakkegaard)

Black Horses
There are both recessive and dominant black horses..
The genotype: aa B_ E_ reults in a plain black horse (recessive black)
The genotype: ED_ B_ results in a plain black horse (dominant black). Since the ED allele is epistatic to the alleles in the A series and dominant to the rest of the alleles in the E series, these alleles will have no influence on the colour in the presence of the ED allele.
Black horses are not always equally black. Very black horses might have the sooty factor (Sty) or maybe they are genotypically recessive black and dominant black at the same time. Also pigment density can help explain why some seem to be more black than others.

Now we have an idea about the base coat colours. These are actually the hardest to understand and get the hang of. Once you understand the rules behind the base coat colours, the rest is pretty easy to get the hang of. The other genes that effect horse coat colour, are all genes that in one way or another modify the horse's base coat colour.

(Gerda Mc Verdi - Stutteri Bakkegaard)

Summary of the base coat colours
In short we can say that::
Red horses never carry the gene for black, but they can be carriers of the gene for brown.
Black horses never carry the gene for brown, but they can be carriers of the gene for red.
Brown/bay horses always carry 1 or 2 alleles of the gene for black, and can be carriers og the gene for red.
This means that two red horses will never be able to have anything foals with red base coat colour.
Two black horses will be able to have both black and red foals.
Two brown/bay horses will be able to have both red, black and brown/bay foals..
When testing for base coat colour, it is usually a lot less complicated than what I have explaines about the colours so far. When testeing they usually only look at the A locus and the E locus, which mean that they do not give you an idea about the type or nuance of the colour. For instance it doesn't distinguish between brown or bay horses:
ee aa = Chestnut
ee Aa= Chestnut (carrier of bown or bay)
ee AA = Chestnut (homozygous carrier of brown or bay)
EE aa = Black
Ee aa = Black (carrier of red)
EE Aa = Heterozygous brown or bay
Ee Aa = Heterozygous brown or bay (carrier of red)
EE AA = Homozygous brown or bay
Ee AA = Homozygous brown or bay (carrier of red)

Sooty factor
This consist of the Sty-series in which 2 alleles have been descriped.
Sty: Results in an expression of eumelanic pigment. In the brown or bay horse, the allele has the strongest effect along the back of the horse. In the red horse the allele has a more uniform effect on the whole body..
sty: results in normal colour tone
The gene is dominant, which means that only one copy of the Sty allele is needed to get the effect of the sooty factor. Also it is enough that either the mare or the stallion has the gene for the foal to inherit it..

Flaxen mane and tail
In english a light mane and tail on a chestnut horse is called flaxen, and results from the f-series, which consists of 2 alleles.
F: Creates a normal colour, meaning red mane and tail in the chestnut horse.
f: results in a light/straw, creme or white mane and tail in the chestnut horse.
The effect of the gene is only seen in chetsnut horses, but the gene can be carried hidden in other colour horses.
Since the gene is recessive, 2 alleles are needed to create an effect. (FF = no effect, Ff = no effect, but heterozygous carrier of the allele, ff = effect and homozygous carrier of the allele)
Both the mare and the stallion need to carry the allele, for the foal to recieve a flaxen mane and tail. If both the mare and the stallion has the colour, then they will both be homozygous for the allele and will therefore both pass on the allele to the foal, resulting in a foal with flaxen mane and tail.

(Bakkegaard's Moonlightning - Stutteri Bakkegaard)

Gray and roan horses
There are two types of horses in which their colour is diluted by the mixture with white hairs: The fading and the permanent. Both genes result in white hairs being mixed in with the horses normal colour, but whereas the gray horses will have progressively more and more white hairs mixed in the older they get until they are completely white, the roan horses do not and will never be completely white. A few roan horses will get a bit more white hairs mixed in with age, but not at all to the same extent as with the gray horses. The roan horses can show very great veriations in their colour, depending on the season (eg, summer, whinter ect.), which is allso why they are often called colour alternators.
There is an additive effect of the two genes, as horses that carry both G and R look like roans at as a foal, but will fade quickly.

Gray horses
The "grey" or "gray" horses result from the dominant allele of the G-series which contains 2 alleles.
G: Gives a continuous and progressive mixture of white hairs in with the normal colour, until the horse in completely white.
g: has no effect on the normal colour.
The foal fur can be any colour and only as the horse grows, the white hairs start to appear. No matter what the initial colour is, the horse is called a gray horse.
In the so called "fleabitten" colour, the horse gets little black or white spots in the white fur once they have completely faded to white.
Depigmentation of the skin can occur in gray horses as they get older, especially around the eyes and muzzle, which results in fleshcoloured skin..
The gene is dominant and is expressed in horses both heterozygous and homozygous for the domanint allele. This means that as long as either the mare or the stallion is gray, then th foal has the possibility of turning gray as well..

(Halstock Cinnamon - Gray - Stutteri Bakkegaard)

Roan horses
Are also called colour alternators, as the amount of white in the coat often chages with the season.
Roan horses always have more than 50 % white hairs in the coat. Horses with less white hairs are not consideres to be roan.
The roan colour appears when the foal fur is shed..
A black horse with the roan gene is called blue roan, a bay horse is called red roan (despite actually being bay and not chestnut) and a chetnut horse is called a strawberry roan.
R: results in a roan horse.
r: no effect, normal colour.
The gene is dominant, resulting in the colour being transmitted in both the heterozygous and homozygous horses. Not long ago the gene was thought to be lethal in the homozygous state, and that the horses that got the RR genotype therfore are never develop. This however seems not to be the case. A number of roan stallions have been registered as never having produced anything but roan foals. Even despite very large numbers of foal. Statistically this would indicate that these stallions are almost certainly homozygous for the dominant roan allele, and that they are alive and well, and even able to reproduce.
It is enough for the mare or the stallion to have the colour, if you wan't the chance of for a roan foal.

(Stjernen's Mini-Dusty - Blue roan- Stutteri Stjernen)

Dilution genes
There are a number of diluting genes that either dilute the horse's base coat colour or modify the pigment so the colour look lighter.

Dun
The dun coloured horses all carry alleles from the D-series. A black horse with one or two dun alleles become blue dun (grullo), a brown or bay horse becomes golden dun (zebra dun) and a chestnut horse becomes creme dun (red dun)
D: Dilutes both eumelanin og phaeomelanin. Body and neck are diluted more than the legs and the head, which seems darker. Down through the middle of the mane, back and tail is a long dark stripe (the dorsal stripe or eel stripe). On either side ofte the stripe in the mane and tail, is dun colered frostings. Leg barrings might also be present. Collectively this is called wild type pattern. The gene has a distinct effect on all three base coat colours.
d: normal pigmentering, ufortyndet.
The gen is dominant, and therefore onlt the stallion or the mare has to be dun, for the foal to have a chance of inhereting the colour.

The dorsal stripe and slight leg barrings might be visible on horses of other colours. These are pseudo-dorsalstripes and are thought to be connected to the sooty gene. Horses with pseudo- dorsal stripes are not dun and will not be able to breed dun coloured foals. A pseudo-dorsal stripe is often not as distinct as the dun dorsal stripe, and often it is not visible all year round.

(Plumtree Thomasena - blue dun/grullo - Stutteri Bakkegaard) .......(Lille Rosendals Eino - golden dun/zebra dun- foto: Janny Sørensen)

The cream gene
It is from this, the C-series, that you get the colours palomino, buckskin and smoky black. In the horse two allels have been descriped in this series. The C-series is also called the albino series, because in some animal species there is a third and completely recessive allel (c = the albino allele) which is responsible for the true albinos that lack pigment in both skin, hair and eyes, giving them the caracteristic red eyes seen in for instance many rodents. This allele however does not exist in the horse, which is why there are no true albino horses.
C: Has no effect on bese coat colour and results in normal colour
Ccr: Dilutes phaeomelanin but not eumelanin, and it exerts a stronger effect on the longhairs (mane and tail) than on the hairs of the body. The allele therefore dilutes chestnut and brown or bay horses, but not black horses..
The chetsnut horses with 1 allele of the cream gene (ee CcrC) will be palomino.
However just like there are different shades of red in the chestnut horses, there are also different shades og palomino horses.:
The genotype: ee A+_ CcrC results in a very light yellow colour (Isabella)
The genotype: ee AA CcrC results in a warm yellow colour that does not lighten in the winter (Golden palomino or non seasonal palomino)
The genotype: ee At_ CcrC results in a palomino that lighten in the winter (Seasonal palomino)
The genotype: ee aa CcrC results in a very dark palomino with an almost brown coat colour (chocolate palomino) which can be mistaken for a mushroom or silver pony.
The seasonal palominos are born very light, and the golden colour doesn't appear until they shed the foal fur.
Non seasonal or true coloured palominos are born a bit darker, almost apricot coloured, and they keep the golden colour all year round.


Bakkegaard's Bellalightning - seasonal palomino - Shady Acres og Bakkegaard's Sandman - nonseasonal palomino - Stutteri Bakkegaard

Brown or bay horses that recieve 1 allele of the creme gene will be buckskin (yellow-brown with black mane and tail). Buckskin should not be confused whith golden dun, because bucksin horses does not have a dorsal stripe. The buckskin coloured horses also come in a variety of different shades depending on the genotype of the base coat colour.
The genotype E_ A+_ CcrC results in a very light buckskin, which is almost white-yellow on the body (cream buckskin)
The genotype: E_ AA CcrC results in a very warm yellow colour (Golden Buckskin)
The genotype: E_At_ CcrC results in a normal buckskin (standard buckskin)
The black horses that recieve 1 allele of the cream gene will be what is called golden black or smoky black. Most often you won't be able to see that a black horse is carrying the cream gene, although sometimes is has a golden shine to its coat, especially in the summer time.
When a horse recieves 2 alleles of the cream gene, then it will be a so called pseudo albino or BEC (blue eyed cream). Yhese horses are very light, almost completely white and have light blue eyes, white hooves and pink skin. They are not true albinos as many people think, and there are no provable faults with horses that have this colour.
The BEC horses look almost exactly like eachother wether their base coat colour is red, brown or black, but there is still different names for the three genotypes:
A chetsnut horse with 2 alleles of the cream gene is called: Cremello
A brown or bay horse with 2 alleles of the cream gene is called: Perlino
A black horse with 2 alleles of the cream gene is called: Smokey cream

Because the creme gene is dominant, only one allele is needed for a dilution of the base coat colour to occur. This also means that a BEC horse, which always passes on a cream allele, will always make a palomino, bucksin or smokey black foal. For instance a cremello horse will always result in a palomino foal when bred to a chestnut horse.

.........

Stjernen's Mini-Blondie - Palomino (Stutteri Bakkegaard) and Kerswell Sorcerer - Buckskin (Stutteri Bakkegaard)

Bakkegaard's Kong Arhtur - Cremello (Stutteri Bakkegaard)

Silver Dapple or Silver Bay
Is controlled by the S-series which has 2 alleles S and s (or inUSA the Z- series with the alleles Z and n)
S: Dilutes eumelanin but has no effect on phaeomelanin. Mane and tail are diluted more than the hairs of the body.
s: Normal colour, no dilution.
Black and black-brown horses are diluted to a dark grey, blue-grey or dark chocolate colour, with light grey or white mane and tail.
The bay horses are only diluted slightly on the body (the black in the hairs is diluted but not the red), and the legs, tail and mane are all diluted as above, since these are all black on a bay horse. The contrast between body and longhairs is not as big as for the black and blac-brown horses that have the S allele. sometimes the bay horses with a silver allele are very red in colour and are confused with chestnut horses with flaxen mane and tail.
The silver gene has no effect on chestnut horses, but they can carry the gene hidden.
The gene is dominant and therefore only one allele is needed to express the colour..
With the shetland ponies, the breeding of silver dapple and silver bay horses has proved to be a lot harder than expected. I am trying to "break the code" by genotyping as many suspected silver shetland ponies as possible.

Recent: So far all the silver shetland ponies that have been tested, have turned out to be negative for the silver gene and have red base coat colour. My mare Zilver also has red base coat colour and does not carry the silver gene. Therefore a lot is pointing in the direction that the silver colour in shetland ponies is a result of a completely new and undiscovered gene. This mysterious colour is now called mushroom by some. I have decided to investigate this further. First I will test as many mushroom shetland ponies as possible, if they are all negative for the silver gene and all have red base coat colour.
If I get enough mushroom samples, I might later on collaborate with a researcher in USA and a researcher in sweeden, to map the gene.

Mushroom
As already stated, it appears that all the silver shetland ponies are actually the result of a completely new and undiscovered gene,which so far is called mushroom. Since the gene has not yet been mapped, nothing can be said whit certainty, but it looks like the gene might have a simple recessive inherritance pattern. If this is the case, then the mushroom shetland ponies must be homozygous for the mushroom gene, which means they have 2 allels og the gene and therefore allways pass 1 allele to their offspring. However it also means that both the stallion and the mare has to be carriers of the gene, to be able to produce a mushroom foal. This could be the reason why it has been so hard, to breed for this colour. Since the gene seems to be relatively rare still, there will not be a lot of carriers, and therefore it will be rare that a combiantion of two mushroom carriers happen. So far the gene only seems to have effect on red base coat colour. This would mean that if you breed two mushroom ponies, there should be a 100% chance for a mushroom foal. If you breed a mushroom pony with a red carrier, there would be a 50% chance for a mushroom foal. Finally if you bred to chestnut ponies that where both carriers, then there would be a 25% chance for a mushroom foal. The problem is that since the gene has not been mapped yet, there is no way of testing wether a pony is carrying the gene or not. But generally all ponies that have produced mushroom offspring, must be carriers of the mushroom gene. Also all offspring from mushroom ponies would be carriers of the gene. Offcourse all this only applies if it turns out to be true that the gene has a simple recessive inherritance pattern and is only expressed on red base coat colour.

(Zilver Sun v.d. Nijkamphoeve - Mushroom - Shady Acres Mini-Shetlands)

Besides these diluting genes, there is also the Champagne gene (dominant) and the recently found Pearl gene (recessive), but since these genes are not seen in the shetland pony breed, I will not explain these further.

An additive effect is seen when a horse carries different dilution genes. For instance a horse that carries both the dun and the silver gene, is diluted even more than if it only carried one of the two. The dun gene dilutes the body the most, and the silver gene will dilute the mane and tail the most. Brown or bay horses become almost like a dark palomino colour with dapples, and black horses become almost silver or light blueish grey, with light grey or white mane and tail. Eyes and skin stay dark. When the dun gene is mixed with a creme gene on a red base coat colour, the result is a milky white body with a light red dorsal stripe, or a very light palomino coloured body with distinctive wildtype pattern.
When mixing the dun gene with a creme gene on a brown or bay base coat colour, the result is a milky white body with black or brown wildtype pattern, and if the horse has a black base coat colour the result is a more light grey/mouse grey body, possibly with a darker head, and with black wildtype pattern.
When mixing a dun gene with 2 alleles of the cream gene, you get a horse with a coat colour like the BEC horses (cremello, perlino and smokey creme), but with a hint of wildtype pattern. Blue eyes and light skin.
Horses that inherit bot a silver gene and a gray gene, are born with gray coat colour, and some are even born completely faded, meaning completely white.
Because off these additive effects, I think it makes it even more interesting to work with these dilution genes, sinve there is the possibility of a wide variety of colours.

Pied Horses
There are several different genes that result in horses whit smaller or larger white areas in their coat. The different genes gives rise to different colour patterns. All known colours can be pied. There are both dominant and recessive genes for pied colour patterns. The horses can also have a mixture of different pied genes, which also has an influence on the color pattern.
A black pied horse is called Piebald
Any other colour pied horse is called a skewbald.
Often descriptions like palomino pied, or golden dun pied are used to describe the colour of a horse.

Tobiano (T)
This is the most common pied gene in european horses, and amongst the shetland ponies. The gene is dominant and results in areas of white, usually extending across the back, and white legs. The coloured areas usually cover the head and more or less of the flanks, plus possibly the and underneath the neck, on the breast and the backside of the thighs. The pigmented areas are usually well defined, with regular edges. The amount of white can vary greatly, from almost completely white (maximal tobiano) to completely self-coloured with few white hairs in the mane and tail (minimal tobiano). Furthermore "inkspots" can appear, which are small distinct dark markings within the white areas, or "pawprints" which are small dark spots that sort of fades in with the white areas. Glaseyes (light blue or white) can be seen in some tobiano coloured horses..
T: Tobianopied
t: Self-coloured

Overo (O)
This gene is mostly found in american horse breeds, and is rarely seen in the shetland ponies (primarily in the american shetland ponies). The gene can also be mixed with the gene for tobiano, and then the colour is referred to as tovero pied. The overo pied horses usually have a wide blaze or a white face. The back is usually coloured. They usually have coloured legs, unless they have white markings resulting from another gene. There are several patterns which have been misnamed overo, but the true overo horses are called "frame overo", because the white areas are framed by the coloured areas. The edges of the white areas are irregular, angular and frayed. The gene is dominant and lethal in the homozygous horse, which means that foals that are homozygous for the overo gene, are born with a nervous-defect in the intestinal system, making them incapable of surviving. They are born white with blue eyes, (not to be mistaken for BEC horses, which are perfectly healthy) and the phenomenon is called Lethal White Foal Syndrome (LWFS).
Oo: Overo pied horse
oo: Self-coloured horse
OO: Whiteborn foal that doesn't survive.
Therefore you should never breed two overo horses to eachother, since there would be a 25 % risk of a LWFS foal. Unfortunately the overo gene can have incomplete penetrance, which means that sometimes a horse can carry the gene without expressing the overo pattern. (even though the gene is dominant). This is a big problem for breeders of for instance American Paint Horse, which is why many of the breeders now genotype the selv-coloured (non overo) horses, to make sure they are not hidden carriers of the gene.

Splashed White (spl)
The gene is only expressed in the homozygous form and is not a colour you come across often.
The gene results in a mostly selv-coloured horse with a white face and white areas on the sides, possibly also with a white belly and white legs. The transition between white and coloured areas is irregular and jagged, and it sometimes looks like a white horse has had paint poured over it. The gene is thought to be recessive, meaning it takes to copies of the allele to see the full effect of the gene. It is speculated that the gene might be incomlete dominant, because you often see little sigs in the heterozygous horses (eg. glass-eyes, big asymetric blazem, a single white spot often on the thigh or similar signs), and a full pattern in the homozygotes. Glass-eyes are frequently connected to the Spl gene.
Spl: Self-coloured horse (possibly with small signs)
spl spl: Splashed white pied

Sabino (Sb)
There is some doubt wether this gene exist in the shetlland breed, but the gene is seen in a number of cold blooded european breeds. The white areas are found on the legs and possibly the belly. The transition between the white and coloured areas is gradual and sometimes almost roaned. Often there are also markings in the head, including helmet blaze, which can stretch across the eyes and give rise to glass-eyes. The gene is dominant.
Sb: Sabino pied horse
sb: Self-coloured horse

Recessively pied and white markings
There is a large number of genes controlling the white markings of a horse. The more of these genes the horse carries, the more white will be present on the horse. The recessively pied horse often has a white belly and a white face, often with almost whote eyes (glass-eyes). Underneath the face is also often white and the edges of the colored areas are often jagged.
Horses can have a wide range of white markings. Socks, blaze, star, helmet blaze, white pasterns and so forth. they are caused by the same genes that, whe present in large enought numbers produce a recessively pied horse.



Bakkegaard's Tinylightning - Splashed White? - Stutteri Bakkegaard and Bakkegaard's Mistylightning - Tobiano - Stutteri Bakkegaard

Stjernen's Surprise - Tobiano with pawprints - Stutteri Bakkegaard and Bakkegaard's Amandalightning - tobiano palomino pied

Sources:

Hestens Farver af Anne Pfaff Ussing, Nucleus, 2000
Genetics - from genes to genomes af Hartwell et. al., McGraw Hill, 2008
http://www.vgl.ucdavis.edu/services/coatcolorhorse.php
http://www.morgancolors.com/index.htm
http://www.pintoheste.dk/Farver.htm
http://www.doubledilute.com/
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1617113

http://www.stutteri-brogaard.dk/side.asp?Id=7441


 

     
bsp;     ody>