HRM Coat Breeding

## **HRM Horse Coat Genetics**

This section is dedicated to the HRM coat genetics. It is one part of the game that is misunderstood and understated in use, but when breeding is planned it can create remarkable looking horses. The coat genetics part of the game is very accurately balanced to the calculation of possible offspring coat colours and the probabilities with parents carrying the dominant or recessive genes.

## **HRM Genetics**

### **Example of HRM Genetics**

In the game the triggers are defined by numbers. In simple terms, 0 = Not Active; and 1 = Active (with 2, 3, 4 as variations to genes but defined as active). As an example, the below shows the use of 0, 1, 2, 3, within the phenotypes.

In the Cream gene (Cr and Prl), the following refers to the games number system used in the genetics:

* 0 = Not Active (n);
* 1 = Active - Pearl (Prl) or Apricot; and
* 2 = Active - Cream (Cr).

Cr and Prl, interfere with each other, that's why they are grouped together. Your horse breed only allows one of the two, refer to the corresponding numbers to know which gene is referred.

In the Agouti gene (At, A, a, and A+), the following refers to the games number system used in the genetics:

* 0 = Not Active - remains Chestnut 'Red' or Black (a);
* 1 = Active - Seal Bay (At);
* 2 = Active - Bay (A); and
* 3 = Active - Wild Bay (A+)

If your horse is chestnut based (see below), this gene will have no visible effect on the coat colour, the horse remains chestnut.

## **Horse Coat Basics**

Genetically, all horses start out as either Chestnut (Red), which is represented in the game by the absence of the extension gene ("Eumelanin") 0-0; or Black (Ebony) based on the presence of the extension gene ("Eumelanin") 1-0, 1-1 or 0-1. The Bay colour is expressed when a common genetic modifier, the Agouti gene, works on Black. The vast range of all other coat colors are created by additional genes' action upon one of these three coat colours.

## **Eumelanin (Extension Gene)**

*Eumelanin* is the gene that determines the basic colour of the horse. As per above all horses start out as Chestnut or Black.

In the Eumelanin (Extension) gene (e or E), the following refers to the games number system used in the genetics (classed as *Extension phenotypes*):

* 0 = Not Active - Chestnut (Red) (e); and
* 1 = Active - Black (Ebony) (E).

### Eumelanin Phenotypes

* ***EE*** (*1-1*) Dominant. Horses with this genotype will be bay, only if it has the non-dun mutation and the 'wild-type' version of other allele (variant form of a gene). Otherwise, the horse could be Black, Seal Bay, Buckskin, Perlino or Smokey Cream, Bay Dun or Grullo, Bay Silver or Black Silver. They may also be Grey or White. Horses that are EE (1-1) will always pass on a functional copy of the *Eumelanin* gene to its offspring, and will never produce offspring with the ee genotype.
* ***Ee*** or ***eE*** (*1-0 or 0-1*) Horses can be any of the same colors as with *EE*, but only have half a chance to pass on a functional Eumelanin.
* ***ee*** (0-0) Recessive. Horses with this genotype will be Chestnut, only if it has the non-dun mutation and the 'wild-type' version of other allele. Otherwise, it can be any of the red-based colors: Red Dun, Palomino, Cremello, Gold Champagne, etc. Just like *EE* horses, they can also be Grey or White. Paired with an *ee* right, such horses will only ever produce red-family coat colors.

A horse that has 'Ee' (1-0), 'eE' (0-1) or 'EE' (1-1) in-game against Eumelanin indicates that the horse is base coat Black (Ebony).

A horse that has 'ee' (0-0) in-game against Eumelanin indicates that the horse is base coat Chestnut.

## **Agouti Gene**

*Agouti* controls the restriction of true black pigment (Eumelanin) in the coat. Horses with the normal agouti gene have the genotype *AA* or *Aa*. Horses without a normal agouti gene have the genotype *aa*, and if they are capable of producing black pigment, it is uniformly distributed throughout the coat.

In the Agouti gene (At, A, a, and A+), the following refers to the games number system used in the genetics (classed as *Agouti phenotypes*):

* 0 = Not Active - Remains Chestnut 'Red' or Black (a);
* 1 = Active - Seal Bay (At);
* 2 = Active - Bay (A); and
* 3 = Active - Wild Bay (A+).

### Agouti Phenotypes

* ***AtAt*** (1-1) 'Mutation' of Agouti known as Brown or Seal Bay. In the absence of a dominant *E* allele. The presence of the Agouti mutation *At* A is responsible in modifying the coat by restricting eumelanin in the coat to the points of the horse (legs, ears, mane and tail). In the presence of at least 1 dominant *E* allele, the mutation results in what is a 'Brown/Seal Bay (horse)' coat colour. Variations of the Brown/Seal Bay coat colour include:
	+ Dark Buckskin (Smokey Brown). A brown based horse with 1 Cream (Cr) gene (1-0 or 0-1);
	+ Perlino. A brown horse with 2 Cream (Cr) genes (1-1, 2-0 or 0-2);
	+ Brown Dun. A brown based horse with at least 1 Dun (D) gene (1-0 or 0-1); and
	+ Sable Champagne. A brown based coat with at least 1 Champagne (CH) gene (1-0 or 0-1).

* ***AA*** (2-2) Bay. The horse may be Bay, Buckskin, Bay Dun, Amber Champagne or Grey, or any member of the Red family. However, such a horse will never be Black, Grullo, and so on, nor will a the *A* horse ever produce uniform-black offspring or Seal Bay offspring.
* ***AAt*** (2-1 or 1-2) Agouti. Visually Indistinguishable from the *A* Bay coloured horse. These horses are unable to produce Black coloured foal.
* ***Aa*** (2-0 or 0-2) 'wild-type' Agouti. Visually Indistinguishable from *A* Bay. Breeding with the right partner, the horse has the ability to produce Black coloured foals.
* ***Ata*** (1-0 or 0-1) These horses have the ability to produce Black and black based coloured horses.
* ***aa*** (0-0) Recessive. In the presence of a dominant *E* allele, the horse's coat will be black. The horses colour can also include changes from others genes like:
	+ The presence of a single Cream (Cr) gene, the coat will be smokey black;
	+ The presence of 2 Cream (Cr) genes the coat will be smokey cream;
	+ The presence of at least 1 Dun (D) gene will result in a Grullo coloured coat (Black Dun);
	+ The presence of at least 1 Champagne (CH) gene will result in classic champagne coa; and
	+ The presence of the at least 1 Silver (Z) gene will turn the black coat into a silver black coat.
* ***A+A+*** (3-3) Wild Bay. The most rare of all the Agouti alleles is the ***A+*** allele. It creates a 'wild-type' bay which will have a black mane and tail like a regular bay. The black on its legs only extends as high as the ankle and often the horse's red colour is somewhat lighter.

## **Dun Dilution**

*Dun* is one of several genes that control the saturation (dilution) or intensity of pigment in the coat. *Dun* is unique in that it is simple dominant, affects eumelanin and pheomelanin equally. The *Dun* gene dilutes both red and black pigment selectively. It retains certain areas and creates certain patterns in the horses original colour. Each Dun horse may have a different combination of markings, all dun horses have the dorsal stripe and some leg barring. The dorsal stripe is a dark stripe that runs along the horse's spine, and the leg barring refers to 'zebra-like stripes' on the horse's legs.

The Dun gene affects both red and black pigment and for this reason, it can create three basic types of dun: the red dun, classic dun, and Grullo.

In the Dun gene (D and d), the following refers to the games number system used in the genetics (classed as *Dun phenotypes*):

* 0 = Not Active - Non-Dun (d); and
* 1 = Active - Dun (D).

### Dun Phenotypes

* ***DD*** (*1-1*) 'wild-type', Dominant. The horse may be, Bay Dun, Grullo, Red Dun, Palomino Dun, Amber Dun, and Grey. This horse will always pass on the *D* allele and will therefore always have dun offspring.
* ***Dd*** (*1-0 or 0-1*) 'wild-type'. Visually indistinguishable from the *D allele* horse.
* ***dd*** (*0-0)* non-dun, Recessive. The entire coat, barring the influence of other alleles, is a rich, saturated colour. The markings are no longer visible. The horse may be Chestnut, Bay, Black, Grey, Palomino, and other variations.

## **Cream / Pearl Dilution**

*Cream* is one of the genes that controls the saturation or dilution of pigment in the coat. *Cream* differs from *Dun* in that it affects the coat, skin, and eyes, and unlike *Dun*, is dosage dependent rather than simple dominant. Furthermore, the effects on eumelanin and pheomelanin are not equal. Horses with the homozygous recessive genotype (*nn*) are not affected by cream. Heterozygotes (*Crn*) have one cream allele and one wildtype non-cream allele. Homozygotes (*CrCr*) have two cream alleles, and are sometimes called "double-dilutes."

The third allele of the cream gene was a recent discovery. It is called "pearl" or the "Barlink factor." A single allele of pearl on its own will do nothing. But with a dominant cream allele as well, it will enhance the cream allele and result in a pseudo double dilute. Two pearl alleles result in a warm dilution color sometimes refered to as "apricot."

In the Cream (Pearl) gene (Cr and Prl), the following refers to the games number system used in the genetics (classed as Cream *phenotypes*):

* 0 = Not Active - Non-Cream (n);
* 1 = Active - Pearl (Prl)
* 2 = Active - Cream (Cr).

### Cream (and/or Pearl) Phenotypes

* ***nn*** (0-0) 'wild-type'. Visually, the horse may be any colour other than the cream dilute shades of palomino, buckskin, smoky black, cremello, perlino, smoky cream, and so on (Chestnut, Bay or Black).
* ***nPrl*** (0-1) The horse is positive for pearl, having inherited the trait from one parent. No visual change to the horse, except for in the additional presence of the cream dilution gene. The horse will pass the pearl dilution gene to approximately half of foals when bred.
* ***PrlPrl*** (1-1) The horse is positive for pearl, and carries two inherited copies of the gene. The phenotype of the homozygous pearl horse will be of dilute appearance, regardless of the presence of cream dilution. The homozygous pearl specimen will pass the pearl gene to 100% of foals, but may only produce diluted offspring if bred to another pearl or cream carrier.
* ***nCr*** (0-2 or 2-0) The most common associated colours with this genotype are palomino, buckskin, and smokey black, though the phenotype may vary depending on other factors. Any pheomelanin in the coat is diluted to yellow or gold.
* ***CrPrl*** (2-1 or 1-2) The horse is a psuedo-double cream with pale skin and eyes.
* ***CrCr*** (2-2) The most common associated colours with this genotype are cremello, perlino, and smokey cream. The coat will be Cream or Ivory-coloured.

## **Champagne Dilution**

*Champagne* is a gene that controls the saturation or dilution of pigment in the coat. Unlike *Cream*, *Champagne* is not strongly dosage-dependent, and affects both types of pigment equally. *Champagne* also differs from *Dun* in that it affects the colour of the coat, skin, and eyes, and in that the unaffected condition is the wildtype. Horses with the dominant *CH* allele (*CHCH* or *CHch* genotype) exhibit hypomelanism of the body coat, such that phaeomelanin is diluted to gold and eumelanin is diluted to tan.

In the Champagne gene (CH), the following refers to the games number system used in the genetics (classed as Cream *phenotypes*):

* 0 = Not Active - Non-Champagne (ch); and
* 1 = Active - Champagne (CH).

### Champagne Phenotypes

* **chch** (0-0) 'wild-type', Recessive. Visually, the horse may be any colour other than the champagne shades.
* **CHch** (1-0 or 0-1) The colours most commonly associated with this genotype are gold champagne, amber champagne, and classic champagne, though the exact phenotype depends on a variety of factors. At birth, the skin is bright pink and the eyes bright blue, darkening to freckled and light brown or green, respectively, with age. Both red and black pigment in the hair are also diluted.
* **CHCH** (1-1) Champagne. Homozygotes, which will never produce non-champagne offspring, are indistinguishable from heterozygotes except that their freckling may be sparser, and their coats a shade lighter.

## **Other Coats**

* Silver
* Appaloosa (incl. PTN1 & PTN2)
* Rabicano
* Roan
* Overo
* Splashed
* Tobiano
* Sooty Double-Splashed
* Fewspot Appaloosa

## Colour Modifiers

* Grey
* Sooty
* Flaxen
* KIT Gene