Coats And Genes

Genetics of the coat color

Gray coat in<br />action
Gray coat in
action
The coat color of a horse is a characteristic that is determined genetically, inherited from parents to offspring following some well-known rules. This fact enables us, by means of the gene analysis, to know in advance the coat color that an individual will have as an adult, and to predict the color of an individual’s descendants. Therefore, the genetic analysis of the coat color opens up a door to selection, aimed reducing a large part of the “luck” component with which at stud farms have historically used.
Currently more than 20 genes have been identified, which are directly or indirectly responsible for the final appearance of the coat, where color, intensity and pigment distribution are concerned. All this could be functionally classified into four types: Basic color genes (Extension and Agouti); Genes that mask other genes (Gray); color dilution genes (Cream, Silver, Pearl, Dun, Champagne); and Genes related to color distribution (Overo, Sabino, Tobiano, etc).
Bay mare with her foal
Bay mare with her foal
Despite the high number of genes implicated in the process, not all of these bear the same weight in the determination of the coat color. There are four genes (Gray, Extension, Agouti and Cream), which are generally responsible for the breed prototypes of the PRE coat color. The Gray gene is responsible for the coat color Gray; the Extension determines the black and chestnut colors in combination with the Agouti, which controls the expression of the eumelanin (black pigment) that originates in the Bay coat colors, and lastly, the Cream gene is responsible for the diluted coat colors. The rest of the genes modulate the previously mentioned basic prototypes and are responsible for the multitudes of variations and shades that can be found naturally.
100% Black PRE
100% Black PRE
With regards to three of the four basic genes responsible for coat color (Extension, Agouti and Cream), molecular studies have been available for some time now, which enable us to find out and predict the coat color of a horse and its possible descendants. In the particular case of the PRE, these studies are of very limited use, as they are only applicable to “non-gray” horses, due to the fact that there was no molecular study available for the gene responsible for the gray coat color. This meant that despite the fact that the genetic analysis of coat color is an enormously useful tool for the breeder, its use as a real utility tool in the PRE was not at all common. Currently the molecular bases of graying in horses is already known, which allows the development of a prediction test similar to those described for other genes such as extension, agouti, cream, etc. So, now, the coat color genetic analysis is applicable to 100% of PRE horses.

Basic genes, genotypes and effects

GENE DESCENDANT HORSE
E
X
T
E
N
S
I
O
N 		EE There are both black and red pigments present in the coat. The horse could be Bay or Black depending on the distribution of the black pigment (given by the Agouti gene) and in the absence of diluting genes (CCr and CrCr). Passes on to offspring the black pigment on points and the possibility of being completely black. Horses with this combination cannot have Chestnut offspring no matter what the genotype of the partner.
Ee There are both black and red pigments present in the coat. The horse could be Bay or Black depending on the distribution of the black pigment (given by the Agouti gene) and in the absence of diluting genes (CCr and CrCr). Could pass the black pigment on to the offspring on points and the possibility of being completely black. On the other hand, could have Chestnut offspring.
ee Only produces red pigment. The horse will be Chestnut in the absence of diluting genes (CCr or CrCr). Only passes on red pigment to offspring.
GENE DESCENDANT HORSE
G
R
A
Y 		GG Masks the pigmentation. The horse will be gray independent of the rest of the genetic formula. The graying process is very fast and there is a greater probability of suffering from melanomas and vitiligo. All the offspring will be gray, independent of what horse it is crossed with.
Gg Masks the pigmentation. The horse will be gray independent of the rest of the genetic formula. The graying process is less homogenous and there is a greater probability of dappling. 50% of this horse’s offspring will be gray, or more if crossed with another gray. The rest will have a normal pigmentation (Black, Bay or Chestnut)
gg Does not mask the pigmentation. The horse displays its coat color (phenotype), which marks the rest of the genes of the genetic formula (genotype). This horse will only produce gray offspring if crossed with a gray horse.
GENE DESCENDANT HORSE
A
G
O
U
T
I 		AA The presence of “A” restricts the black pigment to the points of the horse (Tail, mane, hooves). The horse will be Bay in the absence of diluting genes (CCr and CrCr). This horse cannot have offspring with black coats no matter what the genotype of the partner.
Aa The presence of “A” restricts the black pigment to the points of the horse (Tail, mane, hooves). The horse will be Bay in the absence of diluting genes (CCr and CrCr). This horse cannot have offspring with black or Bay coats
aa This does not hinder the distribution of black pigment throughout the entire body if this is there (EE or Ee). In this case, the horse will be black in the absence of diluting genes (CCr and CrCr). The presence of the allele “a” increases the probability of melanomas. Only passes on information to produce black offspring.
GENE DESCENDANT HORSE
C
R
E
A
M 		CC The presence of “A” restricts the black pigment to the points of the horse (Tail, mane, hooves). The horse will be Bay in the absence of diluting genes (CCr and CrCr). Does not pass on diluting genes to offspring
CCr This produces a single dilution of color. The horse will be Dun, Palomino or Smoky Black depending on the basic coat color and in the absence of other diluting genes. 50% of the offspring will carry the dilution gene
CrCr This produces a double dilution of color. The horse will be Perlino, Cremello or Smoky Cream depending on the basic coat color and in the absence of other diluting genes. All the offspring will have at least one dilution gene; therefore they will be Dun, Palomino or Smoky Black depending on the basic coat color and in the absence of other diluting genes.

Useful Links

The nomenclature used to describe the coats in these links may not coincide whith the one used in this web site.