Colour Simplified
For the experts who deal with colour genetics all the time it is a matter of fact, however for the average lay person it is a minefield and at times hard to get your head around. I have tried to simplify colour genetics as best as I can, adding those definitions and descriptions that the experts take for granted and forget to explain to us.
Photo above of Chocolate Truffles aka Clononeen Laoire and her 2008 Hurricane now of Desert Jewel Gypsy Horses. Photo courtesy of Clononeen Farms
As humans we see colour vividly so it has a certain appeal to many of us. Luckily gypsy vanners come in every colour imaginable. There is only one rare gene that I have yet to see in the gypsy vanners and that is the marbling gene, which I have only seen in my standardbred Sasha. It is a gene that can be as little as 5 years or as long as 15 years to display itself and being a dominant gene we hope that she has passed it on to some of her foals as it is really spectacular and unique.
I profess to be no expert in colour genetics and what I have learnt is by extensive reading, sometimes the same material over and over again so it became crystal clear in my mind. If I have made a mistake or interpreted something wrongly, please let me know so I can correct it. If after reading this you still are uncertain or have questions concerning horse colours, which is understandable, I am always happy to answer your questions. I will try my best to explain in such a way that it is easier to understand.
Here is a brief overview of the main colour genes and how they work. For a better understanding there is an excellent book called Horse Colour Explained by Jeanette Gower in Australia. The book is out of print but she still has a few copies left at a reasonable price. It is very in depth and technical covering all aspects in great detail.
All foals inherit one colour gene from each side of its parents gene pool forming two genes for that particular colour. This is called the Mendelian Inheritance and it is usually represented as two letter such as TT for the Tobiano (pinto) gene or EE for the black/red gene. Each colour gene has been assigned a particular letter(s) of the alphabet....ie CR for Cream, T for Tobiano and so on and so on. When you see a letter in the upper case form it represents the gene is present and the lower case form tells us that the gene is absent. Sometimes you will see the letter N or n, which is basically the same as the lower case representation or telling you the gene is Not present. For a colour gene to display its characteristics visually on the horse it must be a dominant gene. However, some genes are present but do not display their characteristics visually on the horse. This is what we call a recessive or hidden gene. However a recessive gene will display its characteristics outwardly if two copies of the gene are present.
Hence EE tells us that this horse has two copies of the black gene and as the foal will take one of these genes, he will be black or a derivative of black. Ee tells us that the horse has only one copy of the black gene and one copy of the red gene and the horse will be also black or a derivative of black as red is masked or hidden by the dominant black gene. Lastly ee tells us that no copies of the black gene are present and in the absent of any black genes a red based horse is the result.
However, this represents only one side of the equation and once you take into consideration both the sire and the dam's genetic colour codes, the possibilities become more complicated. The diagrams below are called punnet squares that simplify the matter and can be substituted with any colour gene. Once you begin to add more than one colour gene the combinations can become quite confusing, however there is an excellent coat colour calculator at Animal Genetics website. It does require some knowledge of the terminology of the colour genes but with a little reading on the Internet it becomes less confusing. There is also a list of websites below that can help broaden your knowledge about colour in depth.
Links to other websites discussing equine colour.
Mustangs for Us
Horse Colours
The Horse Colour Site
Equnie Colour Genetics
Morgans Colours
The Ultimate Horse Site
CPEA
New Dilutions
Definitions
1) Homozygous - pronounced (hoe-moe-zie-gous). The horse has two copies of a particular gene and it will pass on this gene to all its foals.
2) Heterozygous - pronounced (het-roe-zie-gous). The horse has one copy of a particular gene and “may” pass it on to its foals.
3) Simple Dominant or Dominant Gene – only one copy of the gene needs to be present in order for the gene to display its characteristics visibly. If two genes are present then it manifests no differently than one copy of the gene. A recessive gene can co-exist with a dominant gene such as in the red/black factor (Ee) but the dominant gene will mask the recessive gene.
4) Incomplete Dominant - One copy of the gene will create a slight modification or lightening of the coat, but two copies will produce a double dose of the first effect, either lightening or modifying the coat even more so.
5) Recessive Gene – Two copies of the gene needs to be present in order for the gene to display its characteristics visibly. It can be present as one copy but will not show externally and can be silently passed on showing up many generations later if the combination is right. Other names for a recessive gene are hidden or masked.
6) Dilute Genes – Genes that lighten the base coat colour of a horse. A double dilute is one that lightens the coat twice.
7) Modifying Genes – Genes that modify the colour of the horse generally by de-pigmentation of the coat.
The Colour Genes
Red Black Factor (E)
All horse coats are built on one of two base colours, black (E) or red aka chestnut (e). From here all other genes will have a secondary effect on these two base coats. Black is dominant to red so red is thus recessive or will not display its characteristics outwardly in the present of one black gene.
i) EE - Two copies of the black gene present and the horse will be homozygous for black. All foals will be black, brown or bay. Why is "BAY" included in here....many think bay is a red or chestnut horse but read further about the agouti gene and it will explain all.
ii) Ee - One copy of the black gene present and one copy of the red gene present. The horse will be heterozygous for black and can produce both black or red based foals.
iii) ee - No copies of the black gene present and the horse will always be homozygous for red. The horse will produce red based foals if paired with another homozygous red (ee) horse. If paired with a horse that carries one copy of the red gene and one copy of the black (Ee) then either red and black based foals can be produced again. (NOTE: Some shades of chestnut or reds, ie. black chestnuts are just about undistinguishable from black or brown horses so testing may be necessary if parents genes unknown.)
Agouti (A)
The agouti gene works "only" in conjunction with a black based horse and controls the distribution of black pigment by either distributing it evenly over the entire body (a) or lightening the main body but not the tail, mane and legs leaving them black, called points (A). It is a dominant gene but will hide on a red based horse, as there is no black to dilute. Common names for this colouring of horse are dark bay, light bay and red or blood bay, with buckskin being another name when a single dilution of the cream gene is present. To the gypsies it is called tri-colour when present on a tobiano horse due to the black points, bay body and white tobiano markings. Many bays are confused with a chestnut or red horse because the lightening of the black coat colour can closely resembles a chestnut but the black points tell us it is not a red based horse.
i) AA - Two copies of the agouti gene present and the horse will be homozygous for agouti and the horse will display black points if a black based horse (E). If bred all foals will have black points providing the foal has at least one copy of the black gene (E). NOTE: It is possible for a red base horse to be homozygous for the agouti gene, but again not display it.
ii) Aa - Only one copy of the agouti gene present. The horse will be heterozygous for agouti and if the horse has at least one copy of the black gene (E) it will display black points. The horse can produce both foals with black points and without.
iii) aa - No copies of the agouti gene present and the horse will not display black points and nor can it produce foals with black points, unless the gene is inherited by the other parent.
Pinto Patterns
Gypsy Vanners are usually a mix of many of the pinto patterns. Here is a short list of the composite pinto colours terminology.
1) TOVERO or TOBERO - Tobiano + Frame Overo
2) TOBINO - Tobiano + Sabino
3) TOVINO - Tobiano + Frame Overo + Sabino
4) SABERO - Sabino + Frame Overo
Tobiano (T)
Tobiano is a dominant gene and produces many of the coloured horses commonly seen in the gypsy vanner. Sometimes the tobiano gene may be displayed with only a very small spot of colouring, so at first glance it looks like a solid coloured horse. This is called a minimal tobiano.
i) TT - Two copies of the tobiano gene present and the horse will be homozygous for tobiano. All foals will be tobiano.
ii) Tt - Only one copy of the tobiano gene present. The horse will be heterozygous for tobiano and can produce both tobiano or solid coloured foals.
iii) tt - No copies of the tobiano gene present and the horse will not display characteristics of the tobiano patterns nor can it reproduce tobiano foals, unless the gene is inherited by the other parent.
Frame Overo (O)
Frame Overo is a dominant gene with the base colour of the horse running along the topline between the wither and dock framing irregular, scattered, jagged edged white markings that run underneath the frame along the ribs, neck and body. They usually have large blazes or apron markings on the face and dark feet unless other genes are present.
i) OO - This combination is impossible to achieve as two copies of the overo gene creates a deadly syndrome called Lethal White Overo (LWO). This genetic disorder causes the intestinal system not to develop properly and the foal will die within the first 72 hours after birth when its first meals cannot be digested properly. The lethal white foal will be born almost pure white and testing for the presence of this gene if suspected, is wise before breeding to another overo. If anyone has recorded the Frame Overo gene in the gypsy vanner I would like to know. I am sure they are out there.
ii) Oo (On) - One copy of the gene present and the horse will display frame patterning and carries the LWO gene, but the foals will be normal.
iii) oo (nn) - No copies of the overo gene present and the horse will not display frame overo patterns nor can it reproduce frame overo foals, unless the gene is inherited by the other parent.
Sabino (Sb)
It is currently believed that there are at several expressions of the dominant sabino gene, which accounts for the variability of expression in sabino horses. Some are roany, some have sharp markings, and still others have jagged edges and irregular patches. Currently there is only one test available for Sabino (Sabino 1) and until geneticists discover the other genes it does not mean your horse is not Sabino if he/she tests negative for Sb1. Characteristics of this gene carries a wide range of markings from a sprinkling of roaned like hairs or patches, flecks, a large wide blaze with a white chin spot, blue or partial blue eyes, patches on the underbelly with high white stockings that often extend up the legs of the horse diminishing into spears at the top. It occurs commonly and is not to be confused with roaning.
i) Sb1Sb1 - Two copies of the sabino 1 gene present and the horse is homozygous. Ninety percent or more of his body will be white with dark eyes and is classed as a maximum white sabino. All foals will inherit the sabino gene.
ii) Sb1sb1 (n) - Only one copy of the sabino 1 gene present. The horse will be heterozygous for sabino 1 and can produce foals with or without the sabino 1 gene.
iii) sb1sb1 (nn) - No copies of the sabino 1 gene present and the horse will not display sabino 1 patterns not can it reproduce sabino 1 foals, unless the gene is inherited by the other parent.
Splash (Spl)
Splashed horses look as though they were dipped, feet-first, in white paint. They often have a white or white-tipped tail. Splashed white is theorised to be an incomplete dominant and homozygous splashes will have more white than heterozygous splashes. Splash markings tend to have smooth, crisp edges, and most splashes have a bald face with blue eyes (especially the homozygous ones). Deafness can be an associated characteristic with this gene. To date there is no test for the splash gene.
Creme (Cr)
The cream gene is a dilute as well as an incomplete dominant gene, meaning it is always displayed when it's present, but it acts differently depending if there is one or two copies of the gene present. Horses with one copy of the cream gene (single dilutes) will produced a lightening or dilution of the base coat with no change in the colour of the eyes. A double dose (two copies present) will further lighten or dilute the coat as well as change the colour of the eyes to a blue/green. The cream gene does not effect black hairs in it's single form, only in it's double dose form, but on a red based horse a single dilution lightens the whole coat turning the mane and tail nearly white for your classic palomino.
i) CrCr - Two copies of the cream gene present and the horse will be homozygous for cream. On a black based horse it is referred to a Smokey Cream, a bay based horse is called a Perlino and on a red based horse the result is a Cremello. All will have the classic blue/green eyes of a double dilute.
ii) CRcr - Only one copy of the cream gene present. The horse will be heterozygous for cream and can produce foals with or without the cream gene.
iii) crcr - No copies of the cream gene present and the horse will not display the cream dilution nor can it reproduce cream foals, unless the gene is inherited by the other parent.
Champagne (Ch)
Champagne is another dilution gene and a simple dominant that only requires one copy of the gene to manifest its characteristics on either a black or red based horse to a variety of champagne colouring. It is distinguishable from cream, pearl and dun genes as the champagne horse usually has pink skin, dark freckles particularly around the eyes and muzzle and eyes that can vary from blue, hazel to amber. Unlike cream or pearl there is no difference in the outward characteristic if the horse carries one or two copies of the champagne gene. However if a cream gene is present with the champagne then the cream gene will act as another dilution of the coat causing a further lightening of the horse's colour.
v) CHCH - Two copies of the champagne gene present and the horse will be homozygous for champagne. Champagne on a black horse is called Classic Champagne, on a red horse is called Gold Champagne and on a bay horse is referred to as Amber Champagne.
vi) CHch - Only one copy of the champagne gene present. The horse will be heterozygous for champagne and can produce foals with or without the champagne gene.
vii) chch - No copies of the champagne gene present and the horse will not display the champagne dilution nor can it reproduce champagne foals, unless the gene is inherited by the other parent.
Pearl (Prl)
Pearl is a rare recessive dilution gene that has only just been identified and can work in conjunction with the cream gene. It works very much like the cream gene diluting the coat once or twice, however one dilution of the Pearl gene is barley noticeable on the coat and a double dose of the gene lightens the coat similar to an apricot colour. The double dose does not result in the almost white cremello colouring of the homozygous cream horse. Pearl also acts in conjunction with the cream gene, so by replacing the below possibilities with one cream gene instead of pearl the results will be somewhat similar.
i) PrlPrl - Two copies of the pearl gene present and the horse will be homozygous for pearl. On a black based horse it is referred to a Smokey Cream (an apricot colour). A bay based horse is called a Perlino whereas the mane and tail are partially diluted and appear coffee brown on an apricot body. On a red based horse the result is a Palomino Pearl as the mane and tail are nearly white with the body being a pale palomino colouring. All will have the classic blue/green eyes of a double dilute.
ii) nPrl - Only one copy of the pearl gene present. The horse will be heterozygous for pearl and can produce foals with or without the pearl gene. On a red based horse there will be no change in the colour of the coat thus the gene is hidden and on a black based horse there may or may not be a slight dilution of the coat. However, the presence of one cream gene as well will activate the pearl and act as a double dilution.
iii) nn - No copies of the pearl gene present and the horse will not display the pearl dilution nor can it reproduce pearl foals, unless the gene is inherited by the other parent.
Dun (D)
The Dun gene is associated with primitive markings and lightens or dilutes the body colour while leaving stripes of the original colour along the back, on the upper legs and often other places as well. The dun gene acting on a bay horse is called either a regular dun or zebra dun. At first glance it looks similar to a buckskin, but on closer inspection a dorsal strip will be present on the back, leg barring is generally visible and sometimes a transverse stripe over the withers. The dun gene acting on a black horse is called a Grulla and on a red horse is called a red dun.
i) DD - Two copies of the dun gene present and the horse will be homozygous for dun. All foals will inherit one copy of the dun gene and as it is a dominant gene it will visually display its characteristics.
ii) Dd - Only one copy of the dun gene present. The horse will be heterozygous for dun and can produce foals with or without the dun gene.
iii) dd - No copies of the dun gene present and the horse will not display the dun dilution nor can it reproduce dun foals, unless the gene is inherited by the other parent.
Flaxen (F)
Flaxen is a modifying gene that affects chestnut horse's manes and tails, turning them lighter than the body colour. Some flaxen horses have silver-gray manes and tails instead of the more typical pale yellow or off-white shades of flaxen. This effect is thought to be caused by the sooty modifier acting on the flaxen hairs, effectively "dirtying" their colour. Light flaxen chestnut horses can be mistaken for palomino, and dark flaxen chestnut horses can be mistaken for sooty palomino or silver dapple. Flaxen can "hide" on black based horses, as they do not have red manes and tails to show the effects of flaxen on. Not much is known about the inheritance of flaxen, but it is thought to be recessive.
Silver Dapple (Z)
The Silver Dilution gene is also known as Silver Dapple, taffy in Australia or Chocolate Palomino in the gypsies language. It is a dominant gene but only interacts with a black based horse by diluting or lightening the main body to a chocolate, grey or greyish-brown while leaving the tail, mane and lower legs a silver, blonde or flaxen colour. It is sometimes accompanied by dappling on the body.
i) ZZ - Two copies of the silver dilution gene present and the horse will be homozygous for silver. All foals will inherit the silver gene but only display it if the foal carries at least one copy of the black gene. There has been some research that states that homozygotes with this gene creates ocular changes in the eyes to the point that the eyes are severely affected or almost blind. However, we own a homozygous silver pony mare that has not shown these effects and have also spoke with others in the same position. This is not to say that the research is wrong, but there may be other unidentified factors which influence the ocular changes.
ii) Zz - Only one copy of the silver dilution gene present. The horse will be heterozygous for silver and can produce foals with or without the silver dilution gene.
iii) zz - No copies of the silver dilution gene present and the horse will not display the silver dilution nor can it reproduce silver foals, unless the gene is inherited by the other parent.
left - St. Clarins
photo courtesy of Cielo Celeste Farm
right - Chocolate Truffles aka Clononeen Laoire
photo courtesy of Desert Jewel Gypsy Horses
Grey (G)
Grey is a dominant modifying gene and causes de-pigmentation of the coat over time to either grey or white depending on the base coat. Generally red based foals are born red and turn a pewter or slate grey and black based horses are born black and turn a visual white. The turning of the colours can sometimes take years.
i) GG - Two copies of the grey gene present and the horse will be homozygous for grey. The horse will be grey and all foals will be grey as well. Homozygous grey horses have a tendency to grey out more evenly and sooner than heterozygous grey.
ii) Gg - Only one copy of the grey gene present. The horse will be heterozygous for grey and can produce foals with or without the grey gene.
iii) gg - No copies of the grey gene present and the horse will not display de-pigmentation nor can it reproduce grey foals, unless the gene is inherited by the other parent.
The Spotted Gene
The wild spotting pattern typically seen in the Appaloosa breed is caused by not a single gene but a group of genes called the leopard complex (Lp). Although there currently is no test for this gene we know it to be a dominant gene. The colour of the spots tends to correlate with the colour of the horse's base colour. The Leopard Complex genetics are complicated and not yet fully understood and the pattern can be manifested in several ways:
i) Blanket - A coloured horse with a white area over the hips, sometimes extending onto the back and sides. The point at which the white blanket meets the darker coloured area there is usually a mottling of the two colours resembling a myriad of spots.
ii) Spotted Blanket - Same as above except the blanket has dark coloured spots on it.
iii) Leopard - Large "dark" oval shaped spots interspersed all over on a light based coat, generally white.
iv) Snowflake - The reverse of Leopard, small closely interspersed "light" spots on a darker based coat. The number and size of the spots increases with age.
v) Varnish - Looks like a regular roan except the roaning extends onto the head of the horse and accompanied with spots or blankets
vi) Frosted - Small light sprinkles on a dark based coat.
vii) Few spot - As the name suggests the horse has few spots.
Roan (Rn)
Roan is commonly confused with the Sabino 1 and the grey gene, but is a pattern of individual white hairs sprinkled evenly into the body of the coat with head, legs, ears, mane and tail remaining a solid colour. Once the roan foal has shed out its first coat it basically remains the same colour throughout its life span except for the possible lighting or darkening of colour through the changing seasons. It is a dominant gene and can occur on any base colour, creating some spectacular effects.
i) RR - Two copies of the roan gene present and the horse will be homozygous for roan. However it is believed that the homozygous state of roan is lethal and all but a few foals have died.
ii) Rr - Only one copy of the roan gene present. The horse will be heterozygous for roan and can produce foals with or without the roan gene. A black based horse is called a blue roan, a red based horse is called a strawberry roan and a bay horse is referred to as a red roan.
iii) rr - No copies of the roan gene present and the horse will not display the roaning nor can it reproduce roan foals, unless the gene is inherited by the other parent.
Sooty (Sty)
Also called the smutty gene and it is thought that more and likely a form of natural camouflage for the horse and changes with the season or diet. The Sooty genetic modifier will cause some black hairs to become mixed into body coat, sometimes creating dappling or brindle striping. Dappling has a stunning effect on greys, silver dapples, and sometimes palomino coats and the latter two can be hard to tell apart.
right photo - Duke of Earl
courtesy of Cielo Celeste Farm
left photo - Falcon
courtesy of Irish Tinker Stables
Rabianco
Also called the ticking gene rabicano is a pattern of white hairs sometimes confused with roan. It consists of white hairs interspersed in a faintly brindled pattern along the flank area, belly and up between the front legs. It also causes a "coon tail" of white banding at the tail head. Sometimes this is the only sign of Rabicano and can be easily missed. The rabicano gene is dominant, so rabicano horses will have at least one rabicano parent.
Marbling
Marbling looks like cracked glass or a series of veins in marble itself. It has been extensively recorded in one standardbred sire, Aachen from Australia and all other reports of it were sired by Aachen himself or a descendant of him. It does not begin to show up until later in adulthood and as the years go by it progresses further across the point of the rump and the wither. Our standardbred Sasha has this very rare gene which we originally thought was scarring from harnesses. She started to display it when she was about 5 years of age and it is spreading up to her wither. We have noticed that at certain times of the year it is more prominent. As it is believed to be a simple dominant gene, we hope she has passed it on to some of her foals as it really will be a spectacular gene on the jet black foals that she throws us 50% of the time.
Brindle
Brindle is an extremely rare pattern of vertical striping found all over the body of the horse that looks very much like a brindle dog or cat. Again like the Sooty gene it was probably an ancient form of camouflage.
Bends or Spots
These are spots that appear on the horse and can be seasonal. Breeze, our purebred gypsy vanner filly has two large spots around her shoulder area that are darker than the rest of her coat. Another name for bends of spots is smuts and are commonly found on Welsh Ponies.
