Color Genetics
QUICK KEY:
E = black
e = red
A=agouti(bay)
a = no agouti
Cr = cream
Ch=champagne
G = gray
g = no gray
D = dun
n = negative for a specific gene
Palomino Roan
Yellow Roan of Texas
Yellow Roan of Texas
Buckskin Dun/Dunskin
Hollywood Dun It
Hollywood Dun It
Grulla/Black Dun
Bueno Blue Badger
Bueno Blue Badger
Amber Champagne
Skippin the Bars
Red Roan
Peptoboonsmal
Skippin the Bars
Red Roan
Peptoboonsmal
Each of my breeding horses' has the genotype annotated on their page.
To the right is a quick key to help understand equine color notations. Below is a simplified explanation of just a few color genetics possibilities. If I did not cover something specifically, please email me; I'm trying to keep the page from being too long.
PLEASE EMAIL WITH SPECIFIC QUESTIONS about color possibilities out of your mare. I love figuring out the genetic color puzzles.
Homozygous & Heterozygous:
Homozygous means a horse has 2 of the same gene.
If the genes are the same on each side of the slash (e.g. E/E) then the horse is homozygous for that gene.
If a horse has different genes on either side of the slash, then it is heterozygous (e.g. E/e). If you hear the term "double homozygous," it must be referring to 2 different types of genes, not just 2 of the same gene.
Base Coat Colors:
Each horse has two gene options for its base coat color, black(E) or red (e). All other color genes, like agouti or dun, are color modifiers. A bay horse can be thought of as a black horse with one or 2 agouti genes. It is possible to have a "homozygous black" bay horse. Only one agouti gene is needed to have a bay horse. It is also possible to have a black horse with a red gene (E/e) because black is dominant over red; this kind of black horse could still have sorrel or bay foals.
E/E or E/e, a/a = black horse
E/E or E/e, A/A or A/a = bay horse
e/e, a/a or A/A or A/a = sorrel/chestnut horse
Example:
E/E, A/A = "homozygous black" bay horse
Dominant & Recessive Genes:
Many genes go by the Mendelian rules for dominant or recessive. A horse only needs 1 dominant gene to have an effect on the coat color and is generally annotated with capitalized letters. If the gene annotations are lower case (recessive) the horse must be homozygous for those genes to have an effect on the coat color.
To make matters slightly more confusing, genetic testing labs will often annotate the absence of a gene with either an "n" for negative or the lower case letter. However, these same labs will usually send a detailed key to the abbreviations of your horse's test results.
Examples:
A = dominant agouti gene
A/a = 1 agouti gene and the absence of 1 agouti gene
a/a = the horse does not possess an agouti gene at all
A/n = A/a
Ch = dominant champagne gene
Ch/n = 1 champagne gene and the absence of the other
Ch/ch = Ch/n
Modifier Genes:
Champagne, dun, agouti, and gray are all coat color modifiers. All of these are dominant genes and only one is necessary to have the full affect on a horse's coat color. Gray will trump everything so no matter what the horse's color when born, it will always turn gray. Champagne and dun are additionally dilute genes and will lighten the horse's coat color among other characteristics.
Agouti:
This gene, in my opinion, is the hardest one to understand. The specific definition says that the agouti gene "restricts black to the points." This gene is responsible for bay or buckskin horses. The tricky part is that it only acts on black (E) and does nothing on red (e). So a sorrel horse could have 1, 2 or 0 agouti genes and the only way to find out is either genetic testing OR looking at its offspring. The way I remember agouti is that on a black horse, it "sucks" all the black to the legs, mane, tail and nose. On a red horse: nothing.
Then, of course, it gets more complicated. A recent discovery of a variation of the agouti gene, noted as At, has been found to be responsible for "brown" horses. These horses have mostly been described as seal bay or seal brown, now called sable. Genetically, these horses will test positive for the agouti gene (A/a or A/A) but will physically look very dark brown or even black-ish in the winter. More research is being done on the At gene to determine its exact effects.
Cream Gene:
Cream is a dilute gene and goes by different "rules" than the typical dominant/recessive. The cream gene expression is technically called an incomplete dominant and only has an effect on the red gene (e). All this means is that one cream gene will dilute a sorrel or bay horse's coat color a little bit. Two cream genes will dilute the horse's coat color a lot. Buckskins and palominos each have one cream gene. Cremellos and perlinos have 2 cream genes (homozygous) and will always pass one cream gene on to its offspring. However, since cream only effects the red gene, a black horse can also carry a creme gene. This color is called smokey black. The funny exception to this is that a black horse with 1 cream gene still looks black; but a black horse that is homozygous for the cream gene (called a smokey cream) will look off white and have blue eyes.
Champagne + Cream:
This is a layering of 2 different dilution genes but the horse is heterozygous for both cream and champagne (Cr/cr, Ch/ch). These horses' coat colors look anywhere from white to a light mocha color. Gold cream, amber cream, sable cream and classic cream horses are all horses with 1 cream gene and at least 1 champagne gene with different colored base coats. These horses used to be referred to as ivory, though there was no distinction between a horse with a bay base coat and a sorrel base coat. For the most in depth explanation please visit this page on the ICHR's website.
Roan:
The roan gene simply intersperses white hairs into a horse's base coat giving a basic appearance of a "washed out" horse. Roaning will not touch the extremities of the horse though any amount of white hairs will show up on the body. To date, there is not a genetic test for a roan gene. However, it seems to follow the dominant/recessive rules based on progeny histories. UPDATE: UC Davis now has a test for roan; however, it is not specifically for the roan gene. It seems that the presence of the roan gene in a horse also presents some particular protein markers which can be tested for. In essence, expect more false positives than when testing for a particular gene, but it is a step in the right direction.
Summary:
Equine color genetics are anything but simple. If you have any specific questions please email me and I will do my best to answer them. Please visit the contacts and links page for links to a good color calculator and colors web page.
*Note: I recently wrote a guest article for The Equinest online horse information site on the particulars of the champagne gene.*
To the right is a quick key to help understand equine color notations. Below is a simplified explanation of just a few color genetics possibilities. If I did not cover something specifically, please email me; I'm trying to keep the page from being too long.
PLEASE EMAIL WITH SPECIFIC QUESTIONS about color possibilities out of your mare. I love figuring out the genetic color puzzles.
Homozygous & Heterozygous:
Homozygous means a horse has 2 of the same gene.
If the genes are the same on each side of the slash (e.g. E/E) then the horse is homozygous for that gene.
If a horse has different genes on either side of the slash, then it is heterozygous (e.g. E/e). If you hear the term "double homozygous," it must be referring to 2 different types of genes, not just 2 of the same gene.
Base Coat Colors:
Each horse has two gene options for its base coat color, black(E) or red (e). All other color genes, like agouti or dun, are color modifiers. A bay horse can be thought of as a black horse with one or 2 agouti genes. It is possible to have a "homozygous black" bay horse. Only one agouti gene is needed to have a bay horse. It is also possible to have a black horse with a red gene (E/e) because black is dominant over red; this kind of black horse could still have sorrel or bay foals.
E/E or E/e, a/a = black horse
E/E or E/e, A/A or A/a = bay horse
e/e, a/a or A/A or A/a = sorrel/chestnut horse
Example:
E/E, A/A = "homozygous black" bay horse
Dominant & Recessive Genes:
Many genes go by the Mendelian rules for dominant or recessive. A horse only needs 1 dominant gene to have an effect on the coat color and is generally annotated with capitalized letters. If the gene annotations are lower case (recessive) the horse must be homozygous for those genes to have an effect on the coat color.
To make matters slightly more confusing, genetic testing labs will often annotate the absence of a gene with either an "n" for negative or the lower case letter. However, these same labs will usually send a detailed key to the abbreviations of your horse's test results.
Examples:
A = dominant agouti gene
A/a = 1 agouti gene and the absence of 1 agouti gene
a/a = the horse does not possess an agouti gene at all
A/n = A/a
Ch = dominant champagne gene
Ch/n = 1 champagne gene and the absence of the other
Ch/ch = Ch/n
Modifier Genes:
Champagne, dun, agouti, and gray are all coat color modifiers. All of these are dominant genes and only one is necessary to have the full affect on a horse's coat color. Gray will trump everything so no matter what the horse's color when born, it will always turn gray. Champagne and dun are additionally dilute genes and will lighten the horse's coat color among other characteristics.
Agouti:
This gene, in my opinion, is the hardest one to understand. The specific definition says that the agouti gene "restricts black to the points." This gene is responsible for bay or buckskin horses. The tricky part is that it only acts on black (E) and does nothing on red (e). So a sorrel horse could have 1, 2 or 0 agouti genes and the only way to find out is either genetic testing OR looking at its offspring. The way I remember agouti is that on a black horse, it "sucks" all the black to the legs, mane, tail and nose. On a red horse: nothing.
Then, of course, it gets more complicated. A recent discovery of a variation of the agouti gene, noted as At, has been found to be responsible for "brown" horses. These horses have mostly been described as seal bay or seal brown, now called sable. Genetically, these horses will test positive for the agouti gene (A/a or A/A) but will physically look very dark brown or even black-ish in the winter. More research is being done on the At gene to determine its exact effects.
Cream Gene:
Cream is a dilute gene and goes by different "rules" than the typical dominant/recessive. The cream gene expression is technically called an incomplete dominant and only has an effect on the red gene (e). All this means is that one cream gene will dilute a sorrel or bay horse's coat color a little bit. Two cream genes will dilute the horse's coat color a lot. Buckskins and palominos each have one cream gene. Cremellos and perlinos have 2 cream genes (homozygous) and will always pass one cream gene on to its offspring. However, since cream only effects the red gene, a black horse can also carry a creme gene. This color is called smokey black. The funny exception to this is that a black horse with 1 cream gene still looks black; but a black horse that is homozygous for the cream gene (called a smokey cream) will look off white and have blue eyes.
Champagne + Cream:
This is a layering of 2 different dilution genes but the horse is heterozygous for both cream and champagne (Cr/cr, Ch/ch). These horses' coat colors look anywhere from white to a light mocha color. Gold cream, amber cream, sable cream and classic cream horses are all horses with 1 cream gene and at least 1 champagne gene with different colored base coats. These horses used to be referred to as ivory, though there was no distinction between a horse with a bay base coat and a sorrel base coat. For the most in depth explanation please visit this page on the ICHR's website.
Roan:
The roan gene simply intersperses white hairs into a horse's base coat giving a basic appearance of a "washed out" horse. Roaning will not touch the extremities of the horse though any amount of white hairs will show up on the body. To date, there is not a genetic test for a roan gene. However, it seems to follow the dominant/recessive rules based on progeny histories. UPDATE: UC Davis now has a test for roan; however, it is not specifically for the roan gene. It seems that the presence of the roan gene in a horse also presents some particular protein markers which can be tested for. In essence, expect more false positives than when testing for a particular gene, but it is a step in the right direction.
Summary:
Equine color genetics are anything but simple. If you have any specific questions please email me and I will do my best to answer them. Please visit the contacts and links page for links to a good color calculator and colors web page.
*Note: I recently wrote a guest article for The Equinest online horse information site on the particulars of the champagne gene.*
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