Equine Coat Colour

Each horse has a basic coat colour, which can be black, bay/brown or chestnut. These basic coat colours are controlled by the Extension and Agouti genes. The Extension gene controls the production of black and red pigment while the distribution of black pigment is controlled by the agouti gene.

The rest of the colour genes act as modifiers (dilution or depigmentation) on the basic coat colour of the horse. There are at least five genes that dilute the coat colour of the horse: Cream, Champagne, Dun, Pearl, and Silver. The pattern genes modify the colour of the horse by deleting colour (depigmentation). These genes include Overo, Sabino, Tobiano, Grey, dominant white, white spotting, Appaloosa spotting and Pattern-1. For Appaloosa spotting VHLGenetics doesn’t offer a test yet.

Within the above described coat colour genes, three genes explain the major differences; the Agouti, Extension and Cream dilution genes. In the table below the possible combinations of the genes are indicated.

Coat Colour

Agouti

Extension

Cream Dilution

Black

a/a

E/E of E/e

N/N

Brown or Bay

A/A of A/a

E/E of E/e

N/N

Chestnut

A/A, A/a of a/a

e/e

N/N

Smoky black

a/a

E/E of E/e

N/Cr

Buckskin

A/A of A/a

E/E of E/e

N/Cr

Palomino

A/A, A/a of a/a

e/e

N/Cr

Smoky cream

a/a

E/E of E/e

Cr/Cr

Perlino

A/A of A/a

E/E of E/e

Cr/Cr

Cremello

A/A, A/a of a/a

e/e

Cr/Cr

 

BASIC COLOUR:

P904 Coat Colour Chestnut

Each horse has a basic colour, which can be black, bay/brown or chestnut. These basic coat colours are controlled by the Extension and Agouti genes. The Extension gene (E-locus) controls the production of black and red pigment. The Coat Colour chestnut test (P904) tests for the genetic status of the Extension gene. The Extension gene has two variants (alleles). The dominant allele E produces black pigment and the recessive allele e produces red pigment. All horses, regardless of their coat colour do have the genetics for black or red pigment. Red horses (for example chestnut, sorrel, palomino and cremello) have two copies of the recessive allele e, also called homozygous ee. Black pigmented horses (for example black, bay, brown, smoky black, buckskin, smoky cream and perlino) have at least one copy of the allele E. They can be homozygous EE or heterozygous Ee.

The Coat Colour Chestnut test encloses the following results, in this scheme the results of the Coat Colour Chestnut test are shown in combination with the possible results for the Coat Colour Agouti test:

Result Chestnut

Result Agouti

Coat Colour

Description

e/e

A/A, A/a or a/a

Chestnut, Sorrel

Only the recessive allele e was detected, the horse is homozygous for red pigment (ee). The basic colour is chestnut or sorrel unless modified by other colour modifying genes. It can only pass on allele e to its offspring.

E/e

a/a

Black

The horse is heterozygous for red pigment (Ee). The basic colour is black unless modified by other colour modifying genes. It can pass on either allele E or e to its offspring.

E/e

A/A or A/a

Bay, Brown

The horse is heterozygous for red pigment (Ee). The basic colour is bay or brown unless modified by other colour modifying genes. It can pass on either allele E or e to its offspring.

E/E

a/a

Black

Only the dominant allele E was detected, the horse is homozygous for black pigment (EE). The basic colour is black unless modified by other colour modifying genes. It can only pass on allele E to its offspring and therefore cannot produce red foals.

E/E

A/A or A/a

 

Bay, Brown

Only the dominant allele E was detected, the horse is homozygous for black pigment (EE). The basic colour is bay or brown unless modified by other colour modifying genes. It can only pass on allele E to its offspring and therefore cannot produce red foals.

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P907 Coat Colour Agouti

Each horse has a basic colour, which can be black, bay/brown or chestnut. These basic coat colours are controlled by the Extension and Agouti genes. The Agouti gene (A-locus) controls the distribution of black pigment. The pigment can be uniformly distributed or distributed to the “points” of the body (mane, tail, lower legs and inside the ears). The Agouti gene has no effect on horses that are homozygous ee for the Extension gene as black pigment has to be present for agouti to have an effect. The Coat Colour Agouti test (P907) tests for the genetic status of the Agouti gene. The Agouti gene has two variants (alleles). The dominant allele A restricts black pigment to the points of the horse (for example in bays and buckskins) and the recessive allele a uniformly distributes black pigment over the entire body. Only when the horse has two copies of the recessive allele a (homozygous aa), the black pigment is evenly distributed. The black pigment is distributed into the points if at least one copy of the allele A is present. All horses, regardless of their coat colour do have the genetics for the distribution of black pigment, but it’s not always physically visible.

The Coat Colour Agouti test encloses the following results, in this scheme the results of the Coat Colour Agouti test are shown in combination with the possible results for the Coat Colour Chestnut test:

Result Agouti

Result Chestnut

Coat Colour

Description

a/a

E/E or E/e

Black

Only the recessive allele a was detected. The black pigment is distributed uniformly. If the horse is not e/e for the Extension gene, the basic colour is black unless modified by other colour modifying genes. It can only pass on allele a to its offspring.

a/a

e/e

Chestnut, Sorrel

Only the recessive allele a was detected. The black pigment is distributed uniformly. Because the horse is e/e for the Extension gene, the basic colour is chestnut or sorrel unless modified by other colour modifying genes. It can only pass on allele a to its offspring.

A/a

E/E or E/e

Bay, Brown

The horse is tested heterozygous for Agouti. The black pigment is distributed into the points. If the horse is not e/e for the Extension gene, the basic colour is bay or brown unless modified by other colour modifying genes. It can pass on either allele A or a to its offspring.

A/a

e/e

Chestnut, Sorrel

The horse is tested heterozygous for Agouti. The black pigment is distributed into the points. Because the horse is e/e for the Extension gene, the basic colour is chestnut or sorrel unless modified by other colour modifying genes. It can pass on either allele A or a to its offspring.

A/A

E/E or E/e

Bay, Brown

Only the dominant allele A was detected. The black pigment is distributed into the points. If the horse is not e/e for the Extension gene, the basic colour is bay or brown unless modified by other colour modifying genes. It can only pass on allele A to its offspring and therefore cannot produce black foals.

A/A

e/e

Chestnut, Sorrel

Only the dominant allele A was detected. The black pigment is distributed into the points. Because the horse is e/e for the Extension gene, the basic colour is chestnut or sorrel unless modified by other colour modifying genes. It can only pass on allele A to its offspring and therefore cannot produce black foals.

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DILUTIONS:

P713 Coat Colour Cream dilution

The cream dilution gene has an effect on both red and black pigment and dilutes the basic coat colour to lighter coat shades. In several breeds this is considered a desirable trait. The Cream dilution gene is responsible for the palomino, buckskin, smoky black, cremello, perlino and smoky cream coat colours. A horse can also carry mutations for other modifying genes which can further affect its coat colour. The Coat Colour Cream dilution test (P713) tests for the genetic status of the MATP gene. The MATP gene has two variants (alleles). The allele Cr is semi-dominant. One copy of the Cr allele dilutes the coat colour with a single dose, resulting in palomino, buckskin or smoky black. Two copies of the Cr allele dilute the coat colour with a double dose into cremello, perlino or smoky cream. The effect on black pigment might be very subtle. Horses with two copies of the Cr allele are also called “double-dilutes” or “blue-eyed cream” and they share a number of characteristics. The eyes are pale blue, paler than the unpigmented blue eyes associated with white color or white markings, and the skin is rosy-pink. The allele N is recessive and does not have an effect on the basic colour.

The Coat Colour Cream dilution test encloses the following results, in this scheme the results of the Coat Colour Cream dilution test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Cream dilution

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

Non-dilute. The basic colour is chestnut or sorrel unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Non-dilute. The basic colour is bay or brown unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Non-dilute. The basic colour is black unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/Cr

e/e + A/A, A/a or a/a

 

Palomino

 

Heterozygous dilute, one copy of the Cr allele. The basic coat colour chestnut/sorrel is diluted to palomino. These colours can be further modified by other colour modifying genes. It can pass on either allele N or Cr to its offspring.

N/Cr

E/E or E/e + A/A or A/a

Buckskin

Heterozygous dilute, one copy of the Cr allele. The basic coat colour bay/brown is diluted to buckskin. These colours can be further modified by other colour modifying genes. It can pass on either allele N or Cr to its offspring.

N/Cr

E/E or E/e + a/a

Smoky Black

Heterozygous dilute, one copy of the Cr allele. The basic coat colour black is diluted to Smoky Black. These colours can be further modified by other colour modifying genes. It can pass on either allele N or Cr to its offspring.

Cr/Cr

e/e + A/A, A/a or a/a

 

Cremello

 

Double dilute, two copies of the Cr allele. The basic coat colour chestnut/sorrel is diluted to Cremello. These colours can be further modified by other colour modifying genes. It can only pass on allele Cr to its offspring.

Cr/Cr

E/E or E/e + A/A or A/a

Perlino

Double dilute, two copies of the Cr allele. The basic coat colour bay/brown is diluted to Perlino. These colours can be further modified by other colour modifying genes. It can only pass on allele Cr to its offspring.

Cr/Cr

E/E or E/e + a/a

Smoky Cream

Double dilute, two copies of the Cr allele. The basic coat colour black is diluted to Smoky Cream. These colours can be further modified by other colour modifying genes. It can only pass on allele Cr to its offspring.

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P853 Coat Colour Champagne dilution

The Champagne dilution gene lightens the coat colour of the horse by diluting the pigment. The skin of Champagne-diluted horses is pinkish/lavender toned and becomes speckled with age; the speckling is particularly noticeable around the eye, muzzle, under the tail, udder and sheath. The eye colour is blue-green at birth and darkens to amber as the horse ages. Champagne has the following effects on the basic coat colours of horses:

Chestnut/Sorrel -> Gold champagne:   a gold body color and often a flaxen mane and tail. Gold champagne horses are visually similar to palomino horses.

Bay/Brown -> Amber champagne:       a tan body color with brown points

                                                             (sometimes referred to as amber Buckskin)

Black -> Classic champagne:               a darker tan body with brown points

A horse can also carry mutations for other modifying genes which can further affect its coat colour. The Coat Colour Champagne dilution test (P853) tests for the genetic status of the SLC36A1 gene. This gene has two variants (alleles). The dominant allele Ch results in the dilution and the recessive allele N does not have an effect on the basic colour.

The Coat Colour Champagne dilution test encloses the following results, in this scheme the results of the Coat Colour Champagne dilution test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Champagne dilution

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Non-dilute. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Non-dilute. The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Non-dilute. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/Ch

e/e + A/A, A/a or a/a

 

Gold Champagne

 

One copy of the dominant Ch allele. The basic colour chestnut/sorrel is diluted to gold champagne unless modified by other colour modifying genes. It can pass on either allele N or Ch to its offspring.

N/Ch

E/E or E/e + A/A or A/a

Amber Champagne

One copy of the dominant Ch allele. The basic colour bay/brown is diluted to amber champagne unless modified by other colour modifying genes. It can pass on either allele N or Ch to its offspring.

N/Ch

E/E or E/e + a/a

Classic Champagne

One copy of the dominant Ch allele. The basic colour black is diluted to classic champagne unless modified by other colour modifying genes. It can pass on either allele N or Ch to its offspring.

Ch/Ch

e/e + A/A, A/a or a/a

 

Gold Champagne

 

Two copies of the dominant Ch allele. The basic colour chestnut/sorrel is diluted to Gold Champagne unless modified by other colour modifying genes. It can only pass on allele Ch to its offspring.

Ch/Ch

E/E or E/e + A/A or A/a

Amber Champagne

Two copies of the dominant Ch allele. The basic colour bay/brown is diluted to amber champagne unless modified by other colour modifying genes. It can only pass on allele Ch to its offspring.

Ch/Ch

E/E or E/e + a/a

Classic Champagne

Two copies of the dominant Ch allele. The basic colour black is diluted to classic champagne unless modified by other colour modifying genes. It can only pass on allele Ch to its offspring.

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P660 Coat Colour Dun dilution

The Dun dilution gene lightens the coat colour of the horse by lightening the body colour, leaving the head, lower legs, mane and tail undiluted. Dun is also typically characterized by “primitive markings”, allmost all dun horses possess at least the dorsal stripe, but the presence of the other primitive markings varies. Other common markings may include horizontal striping on the legs, transverse striping across the shoulders, and lighter guard hairs along the edges of a dark mane and tail. Dun diluted coat colour with primitive markings is considered the “wild-type” colour and is found in wild equids such as przewalski horses. Dun dilutes both red and black pigment, and the resulting colors range from apricot, golden, dark gray, olive and many more subtle variations. A horse can also carry mutations for other modifying genes which can further affect its coat colour. The Coat Colour Dun dilution test (P660) tests for the genetic status of the TBX3 gene. This gene has three variants (alleles); allele D is dominant over the alleles nd1 and nd2; allele nd1 is dominant over nd2. The dominant allele D results in Dun dilution with primitive markings. Allele nd1 does not dilute the coat colour of the horse, primitive markings are present but the expression is variable. Allele nd2 does not have an effect on the basic colour.

The Coat Colour Dun dilution test encloses the following results, in this scheme the results of the Coat Colour Dun dilution test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Dun dilution

Result Chestnut + Agouti

Coat Colour

Description

nd2/nd2

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel. No primitive markings

Two copies of the nd2 allele. Coat colour is not diluted and primitive markings are absent. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele nd2 to its offspring.

nd2/nd2

E/E or E/e + A/A or A/a

Bay, Brown. No primitive markings

Two copies of the nd2 allele. Coat colour is not diluted and primitive markings are absent. The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele nd2 to its offspring.

nd2/nd2

E/E or E/e + a/a

Black. No primitive markings

Two copies of the nd2 allele. Coat colour is not diluted and primitive markings are absent. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele nd2 to its offspring.

nd1/nd2

e/e + A/A, A/a or a/a

 

 

Chestnut, Sorrel. Primitive markings may be present

One copy of the nd1 allele and one copy of the nd2 allele. The nd1 allele is dominant over the nd2 allele. Coat colour is not diluted. Primitive markings may be present. The colour can be further modified by other colour modifying genes. It can pass on either allele nd1 or nd2 to its offspring.

nd1/nd2

E/E or E/e + A/A or A/a

Bay, Brown. Primitive markings may be present

One copy of the nd1 allele and one copy of the nd2 allele. The nd1 allele is dominant over the nd2 allele. Coat colour is not diluted. Primitive markings may be present. The colour can be further modified by other colour modifying genes. It can pass on either allele nd1 or nd2 to its offspring.

nd1/nd2

E/E or E/e + a/a

Black. Primitive markings may be present

One copy of the nd1 allele and one copy of the nd2 allele. The nd1 allele is dominant over the nd2 allele. Coat colour is not diluted. Primitive markings may be present. The colour can be further modified by other colour modifying genes. It can pass on either allele nd1 or nd2 to its offspring.

nd1/nd1

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel. Primitive markings may be present

Two copies of the nd1 allele. Coat colour is not diluted. Primitive markings may be present. The colour can be further modified by other colour modifying genes. It can only pass on allele nd1 to its offspring.

nd1/nd1

E/E or E/e + A/A or A/a

Bay, Brown. Primitive markings may be present

 

Two copies of the nd1 allele. Coat colour is not diluted. Primitive markings may be present. The colour can be further modified by other colour modifying genes. It can only pass on allele nd1 to its offspring.

nd1/nd1

E/E or E/e + a/a

Black. Primitive markings may be present

 

Two copies of the nd1 allele. Coat colour is not diluted. Primitive markings may be present. The colour can be further modified by other colour modifying genes. It can only pass on allele nd1 to its offspring.

D/nd2

e/e + A/A, A/a or a/a

 

Red dun. With primitive markings

One copy of the dominant D allele and one copy of the nd2 allele. Coat colour is dun-diluted with primitive markings. The colour can be further modified by other colour modifying genes. It can pass on either allele D or nd2 to its offspring.

D/nd2

E/E or E/e + A/A or A/a

Bay dun. With primitive markings

One copy of the dominant D allele and one copy of the nd2 allele. Coat colour is dun-diluted with primitive markings. The colour can be further modified by other colour modifying genes. It can pass on either allele D or nd2 to its offspring.

D/nd2

E/E or E/e + a/a

Blue dun. With primitive markings

One copy of the dominant D allele and one copy of the nd2 allele. Coat colour is dun-diluted with primitive markings. The colour can be further modified by other colour modifying genes. It can pass on either allele D or nd2 to its offspring.

D/nd1

e/e + A/A, A/a or a/a

 

Red dun. With primitive markings

One copy of the dominant D allele and one copy of the nd1 allele. Coat colour is dun-diluted with primitive markings. The colour can be further modified by other colour modifying genes. It can pass on either allele D or nd1 to its offspring.

D/nd1

E/E or E/e + A/A or A/a

Bay dun. With primitive markings

One copy of the dominant D allele and one copy of the nd1 allele. Coat colour is dun-diluted with primitive markings. The colour can be further modified by other colour modifying genes. It can pass on either allele D or nd1 to its offspring.

D/nd1

E/E or E/e + a/a

Blue dun. With primitive markings

One copy of the dominant D allele and one copy of the nd1 allele. Coat colour is dun-diluted with primitive markings. The colour can be further modified by other colour modifying genes. It can pass on either allele D or nd1 to its offspring.

D/D

e/e + A/A, A/a or a/a

Red dun. With primitive markings

Two copies of the dominant D allele. Coat colour is dun-diluted with primitive markings. The colour can be further modified by other colour modifying genes. It can only pass on allele D to its offspring.

D/D

E/E or E/e + A/A or A/a

Bay, Classic, Zebra dun. With primitive markings

Two copies of the dominant D allele. Coat colour is dun-diluted with primitive markings. The colour can be further modified by other colour modifying genes. It can only pass on allele D to its offspring.

D/D

E/E or E/e + a/a

Blue, Mouse dun. With primitive markings

Two copies of the dominant D allele. Coat colour is dun-diluted with primitive markings. The colour can be further modified by other colour modifying genes. It can only pass on allele D to its offspring.

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P783 Coat Colour Pearl dilution

The Pearl dilution gene lightens the coat colour of the horse by diluting the red pigment. A chestnut basic colour is diluted to a pale, uniform apricot colour of body, mane and tail. Skin coloration is also pale. Pearl dilution is also referred to as the 'Barlink Factor.' The Coat Colour Pearl dilution test (P783) tests for the genetic status of the SLC45A2 gene. This gene has two variants (alleles). The allele Prl, causing the Pearl dilution is recessive. This means that only horses with two copies of the Prl allele have a lightened coat, mane and tail, in addition to bright eye colors. The dominant allele N does not have an effect on the basic coat colour.

Pearl dilution interacts with Cream dilution to produce pseudo-double dilute phenotypes including pale skin and blue/green eyes. Therefore if a horse has one copy of the Prl allele and Cream dilution (Cr allele) is also present, this results in a pseudo-double dilute, also called pseudo-cremellos or pseudo-smoky cream

A horse can also carry mutations for other modifying genes which can further affect its coat colour.

The Coat Colour Pearl dilution test encloses the following results, in this scheme the results of the Coat Colour Pearl dilution test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Pearl dilution

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

Chestnut, Sorrel

Non-dilute. The basic colour chestnut/sorrel is not diluted unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Non-dilute. The basic colour bay/brown is not diluted unless modified by other colour modifying genes. It can only pass on allele N to its offspring

N/N

E/E or E/e + a/a

Black

Non-dilute. The basic colour black is not diluted unless modified by other colour modifying genes. It can only pass on allele N to its offspring

N/Prl

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

One copy of the recessive Prl allele. The basic colour chestnut/sorrel is not diluted unless modified by other colour modifying genes. If cream dilution is also present, this results in a pseudo-double dilute. It can pass on either allele N or Prl to its offspring.

N/Prl

E/E or E/e + A/A or A/a

Bay, Brown

One copy of the recessive Prl allele. The basic colour bay/brown is not diluted unless modified by other colour modifying genes. If cream dilution is also present, this results in a pseudo-double dilute. It can pass on either allele N or Prl to its offspring.

N/Prl

E/E or E/e + a/a

Black

One copy of the recessive Prl allele. The basic colour black not diluted unless modified by other colour modifying genes. If cream dilution is also present, this results in a pseudo-double dilute. It can pass on either allele N or Prl to its offspring.

Prl/Prl

e/e + A/A, A/a or a/a

 

Pearl dilution

Two copies of the recessive Prl allele. The basic colour chestnut/sorrel is diluted to a pale, uniform apricot colour of body hair, mane and tail. This colour can be further modified by other colour modifying genes. It can only pass on allele Prl to its offspring.

Prl/Prl

E/E or E/e + A/A or A/a

Pearl dilution

Two copies of the recessive Prl allele. The basic colour bay/brown is diluted to lightened coat, mane and tail. This colour can be further modified by other colour modifying genes. It can only pass on allele Prl to its offspring.

Prl/Prl

E/E or E/e + a/a

Pearl dilution

Two copies of the recessive Prl allele. The basic colour black is diluted to lightened coat, mane and tail. This colour can be further modified by other colour modifying genes. It can only pass on allele Prl to its offspring.

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P784 Coat Colour Silver dilution

The Silver dilution gene dilutes the black pigment but has no effect on the red pigment. The effect of the Silver dilution gene can vary greatly. The mane and tail are lightened to flaxen or silver gray, and may darken on some horses as they age. A black horse will be diluted to chocolate with a lightened mane and tail. A Bay horse with Silver dilution will usually have a lightened mane and tail, as well as lightened lower legs (places with black pigment). A horse can also carry mutations for other modifying genes which can further affect its coat colour.

The Coat Colour Silver dilution test (P784) tests for the genetic status of the PMEL17 gene. This gene has two variants (alleles). The dominant allele Z results in the dilution and the recessive allele N does not have an effect on the basic colour.

The Coat Colour Silver dilution test encloses the following results, in this scheme the results of the Coat Colour Silver dilution test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Silver dilution

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Non-dilute. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Non-dilute. The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Non-dilute. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/Z

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

One copy of the dominant Z allele. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can pass on either allele N or Z to its offspring.

N/Z

E/E or E/e + A/A or A/a

Silver dilution on Bay or Brown

One copy of the dominant Z allele. The black pigment of bay/brown horses on lower legs is lightened and mane and tail are lightened to flaxen. The colour can be further modified by other colour modifying genes. It can pass on either allele N or Z to its offspring.

N/Z

E/E or E/e + a/a

Chocolate

One copy of the dominant Z allele. The basic colour black is diluted to chocolate with flaxen mane and tail. The colour can be further modified by other colour modifying genes. It can pass on either allele N or Z to its offspring.

Z/Z

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Two copies of the dominant Z allele. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele Z to its offspring.

Z/Z

E/E or E/e + A/A or A/a

Silver dilution on Bay or Brown

Two copies of the dominant Z allele. The black pigment of bay/brown horses on lower legs is lightened and mane and tail are lightened to flaxen. The colour can be further modified by other colour modifying genes. It can only pass on allele Z to its offspring.

Z/Z

E/E or E/e + a/a

Chocolate

Two copies of the dominant Z allele. The basic colour black is diluted to chocolate with flaxen mane and tail. The colour can be further modified by other colour modifying genes. It can only pass on allele Z to its offspring.

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Patterns:

P591 Coat Colour Dominant White 1

White patterning in horses is known as Dominant White or White. Dominant White patterns are variable, ranging from minimal Sabino-like spotting to all-white horses. The eye colour of Dominant White horses is brown. There are about 20 different mutations identified that are associated with white patterns, all mutations are found in the KIT gene. Except for W20, most of the known Dominant White mutations arose recently and are restricted to specific lines within breeds. The Coat Colour Dominant White 1 test (P591) tests for the mutation known as W18 in the KIT gene. This test detects two variants (alleles). The allele W18 is dominant. One or two copies of the W18 allele result in horses that display some degree of white spotting but the specific pattern cannot be predicted. The allele N is recessive and does not have an effect on the basic colour.

The Coat Colour Dominant White 1 test encloses the following results, in this scheme the results of the Coat Colour Dominant White 1 test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Dominant White 1

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Not Dominant White. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Not Dominant White. The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Not Dominant White. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/W18

e/e + A/A, A/a or a/a

 

Chestnut/sorrel with Dominant White pattern

Dominant White pattern. One copy of the W18 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or W18 to its offspring.

N/W18

E/E or E/e + A/A or A/a

Brown/bay with Dominant White pattern

Dominant White pattern. One copy of the W18 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or W18 to its offspring.

N/W18

E/E or E/e + a/a

Black with Dominant White pattern

Dominant White pattern. One copy of the W18 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or W18 to its offspring.

W18/W18

e/e + A/A, A/a or a/a

Chestnut/sorrel with Dominant White pattern

Dominant White pattern. Two copies of the W18 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele W18 to its offspring.

W18/W18

E/E or E/e + A/A or A/a

Brown/bay with Dominant White pattern

Dominant White pattern. Two copies of the W18 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele W18 to its offspring.

W18/W18

E/E or E/e + a/a

Black with Dominant White pattern

Dominant White pattern. Two copies of the W18 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele W18 to its offspring.

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P592 Coat Colour Dominant White 3

White patterning in horses is known as Dominant White or White. Dominant White patterns are variable, ranging from minimal Sabino-like spotting to all-white horses. The eye colour of Dominant White horses is brown. There are about 20 different mutations identified that are associated with white patterns, all mutations are found in the KIT gene. Except for W20, most of the known Dominant White mutations arose recently and are restricted to specific lines within breeds. The Coat Colour Dominant White 3 test (P592) tests for the mutation known as W20 in the KIT gene. This test detects two variants (alleles). The allele W20 is dominant. One or two copies of the W20 allele have a subtle effect on the amount of white expressed. It appears to increase the expression of white in combination with other white pattern genes. The allele N is recessive and does not have an effect on the basic colour.

The Coat Colour Dominant White 3 test encloses the following results, in this scheme the results of the Coat Colour Dominant White 3 test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Dominant White 3

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Not Dominant White. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Not Dominant White. The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Not Dominant White. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/W20

e/e + A/A, A/a or a/a

 

Chestnut/sorrel with Dominant White pattern

Dominant White pattern. One copy of the W20 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or W20 to its offspring.

N/W20

E/E or E/e + A/A or A/a

Brown/bay with Dominant White pattern

Dominant White pattern. One copy of the W20 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or W20 to its offspring.

N/W20

E/E or E/e + a/a

Black with Dominant White pattern

Dominant White pattern. One copy of the W20 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or W20 to its offspring.

W20/W20

e/e + A/A, A/a or a/a

Chestnut/sorrel with Dominant White pattern

Dominant White pattern. Two copies of the W20 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele W20 to its offspring.

W20/W20

E/E or E/e + A/A or A/a

Brown/bay with Dominant White pattern

Dominant White pattern. Two copies of the W20 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele W20 to its offspring.

W20/W20

E/E or E/e + a/a

Black with Dominant White pattern

Dominant White pattern. Two copies of the W20 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele W20 to its offspring.

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P593 Coat Colour Macchiato (Splashed White)

In 2008 a colt with a striking white-spotting coat colour was born out of two solid-coloured bay Franches-Montagnes parents. The coat colour looks like a combination of white-spotting and coat colour dilution and it was named ‘‘macchiato’’. A clinical examination revealed that the macchiato stallion was deaf and had a low progressive sperm motility.

The Coat Macchiato (Splashed White)  test (P593) tests for a mutation in the MITF gene. This test detects two variants (alleles). The allele M is dominant. One or two copies of the M allele result in the Macchiato coat colour. The allele N is recessive and does not have an effect on the basic colour.

The Coat Macchiato (Splashed White) test encloses the following results:

Result Macchiato

Coat Colour

Description

N/N

Non-Macchiato

 

Non-Macchiato. The basic colour is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/M

Macchiato

Macchiato pattern. One copy of the M allele. Horse has Macchiato coat pattern unless modified by other colour modifying genes. It can pass on either allele N or M to its offspring.

M/M

Macchiato

Macchiato pattern. Two copies of the M allele. Horse has Macchiato coat pattern unless modified by other colour modifying genes. It can only pass on allele M to its offspring.

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P594 Coat Colour White Spotting 1

Splashed white is a variable white spotting pattern characterized by a large blaze, extended white markings on legs, variable white spotting on belly, pink skin and often blue eyes. In other cases, the unpigmented areas are quite small and cannot be distinguished from horses with other more subtle depigmentation phenotypes. Splashed white horses are sometimes deaf, however most splashed white horses are not deaf. Hearing loss is due to the death of the necessary hair cells, caused by the absence of melanocytes in the inner ear. Although the majority of splash horses have pigment around the outside of the ear, the pigment must occur in the inner ear to prevent hearing loss. There are several different mutations identified that are associated with splashed white patterns. The Coat White Spotting 1 test (P594) tests for the mutation known as SW1 in the MITF gene. This test detects two variants (alleles). The allele SW1 is dominant. One or two copies of the SW1 allele result in splashed white. The allele N is recessive and does not have an effect on the basic colour.

The Coat Colour White Spotting 1 test encloses the following results, in this scheme the results of the Coat Colour White Spotting 1 test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result White Spotting 1

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Not Splashed White. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Not Splashed White The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Not Splashed White. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/SW1

e/e + A/A, A/a or a/a

 

Chestnut/sorrel with Splashed White pattern

Splashed White pattern. One copy of the SW1 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or SW1 to its offspring.

N/SW1

E/E or E/e + A/A or A/a

Brown/bay with Splashed White pattern

Splashed White pattern. One copy of the SW1 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or SW1 to its offspring.

N/SW1

E/E or E/e + a/a

Black with Splashed White pattern

Splashed White pattern. One copy of the SW1 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or SW1 to its offspring.

SW1/SW1

e/e + A/A, A/a or a/a

Chestnut/sorrel with Splashed White pattern

Splashed White pattern. Two copies of the SW1 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele SW1 to its offspring.

SW1/SW1

E/E or E/e + A/A or A/a

Brown/bay with Splashed White pattern

Splashed White pattern. Two copies of the SW1 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele SW1 to its offspring.

SW1/SW1

E/E or E/e + a/a

Black with Splashed White pattern

Splashed White pattern. Two copies of the SW1 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele SW1 to its offspring.

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P595 Coat Colour White Spotting 3

Splashed white is a variable white spotting pattern characterized by a large blaze, extended white markings on legs, variable white spotting on belly, pink skin and often blue eyes. In other cases, the unpigmented areas are quite small and cannot be distinguished from horses with other more subtle depigmentation phenotypes. Splashed white horses are sometimes deaf, however most splashed white horses are not deaf. Hearing loss is due to the death of the necessary hair cells, caused by the absence of melanocytes in the inner ear. Although the majority of splash horses have pigment around the outside of the ear, the pigment must occur in the inner ear to prevent hearing loss. There are several different mutations identified that are associated with splashed white patterns. The Coat White Spotting 3 test (P595) tests for the mutation known as SW3 in the MITF gene. This test detects two variants (alleles). The allele SW3 is dominant. One or two copies of the SW3 allele result in splashed white. It is speculated that two copies of the SW3 allele are lethal (the foal dies). The allele N is recessive and does not have an effect on the basic colour.

The Coat Colour White Spotting 3 test encloses the following results, in this scheme the results of the Coat Colour White Spotting 3 test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result White Spotting 3

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Not Splashed White. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Not Splashed White The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Not Splashed White. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/SW3

e/e + A/A, A/a or a/a

 

Chestnut/sorrel with Splashed White pattern

Splashed White pattern. One copy of the SW3 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or SW3 to its offspring.

N/SW3

E/E or E/e + A/A or A/a

Brown/bay with Splashed White pattern

Splashed White pattern. One copy of the SW3 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or SW3 to its offspring.

N/SW3

E/E or E/e + a/a

Black with Splashed White pattern

Splashed White pattern. One copy of the SW3 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can pass on either allele N or SW3 to its offspring.

SW3/SW3

e/e + A/A, A/a or a/a

Chestnut/sorrel with Splashed White pattern

Splashed White pattern. Two copies of the SW3 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele SW3 to its offspring.

SW3/SW3

E/E or E/e + A/A or A/a

Brown/bay with Splashed White pattern

Splashed White pattern. Two copies of the SW3 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele SW3 to its offspring.

SW3/SW3

E/E or E/e + a/a

Black with Splashed White pattern

Splashed White pattern. Two copies of the SW3 allele. The horse will display some degree of white spotting but the specific pattern cannot be predicted, unless modified by other colour modifying genes. It can only pass on allele SW3 to its offspring.

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P659 Coat Colour Roan

Roan is a white patterning coat colour trait of intermixed white and coloured hairs in the body while the head, lower legs, mane and tail remain colored. Roan horses are born with the pattern, though it may not be obvious until the foal coat is shed. The white and coloured hairs are evenly mixed in horses that inherit the classic Roan gene, which can differentiate this from several mimic patterns called roaning. Roaning patterns tend to be uneven in the distribution of white hairs and the inheritance of roaning has not been defined. The mutation causing the Roan coat colour has not yet been identified. The Coat Roan test (P659) tests for DNA markers that are associated with Roan coat colour in several breeds, the DNA markers can be used to determine if a horse has the Roan mutation and how many copies. This test detects three variants (alleles), Rn, Rn* and N. The allele Rn is dominant. One or two copies of the Rn allele result in a Roan coat colour. The allele Rn* is very uncommon and not always associated with the Roan coat colour, this allele has only been observed in Tennessee Walking horses and Rocky Mountain horses. The allele N is recessive and does not have an effect on the basic colour.

The Coat Colour Roan test encloses the following results, in this scheme the results of the Coat Colour Roan test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Roan

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Not Roan. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Not Roan. The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Not Roan. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

Rn/N

e/e + A/A, A/a or a/a

 

Chestnut/sorrel Roan

One copy of the dominant Rn allele. The colour is chestnut/sorrel roan, unless modified by other colour modifying genes. It can pass on either allele N or Rn to its offspring.

Rn/N

E/E or E/e + A/A or A/a

Brown/bay Roan

One copy of the dominant Rn allele. The colour is brown/bay roan, unless modified by other colour modifying genes. It can pass on either allele N or Rn to its offspring.

Rn/N

E/E or E/e + a/a

Black Roan

One copy of the dominant Rn allele. The colour is black roan, unless modified by other colour modifying genes. It can pass on either allele N or Rn to its offspring.

Rn*/N

e/e + A/A, A/a or a/a

Chestnut/sorrel or Chestnut/sorrel Roan

One copy of the uncommon Rn* allele. The colour can be chestnut/sorrel or chestnut/sorrel roan, unless modified by other colour modifying genes. It can pass on either allele N or Rn* to its offspring.

Rn*/N

E/E or E/e + A/A or A/a

Brown/bay or Brown/bay Roan

One copy of the uncommon Rn* allele. The colour can be brown/bay or brown/bay roan, unless modified by other colour modifying genes. It can pass on either allele N or Rn* to its offspring.

Rn*/N

E/E or E/e + a/a

Black or Black Roan

One copy of the uncommon Rn* allele. The colour can be black or black roan, unless modified by other colour modifying genes. It can pass on either allele N or Rn* to its offspring.

Rn/Rn

e/e + A/A, A/a or a/a

Chestnut/sorrel Roan

Two copies of the dominant Rn allele. The colour is chestnut/sorrel roan, unless modified by other colour modifying genes. It can only pass on allele Rn to its offspring.

Rn/Rn

E/E or E/e + A/A or A/a

Brown/bay Roan

Two copies of the dominant Rn allele. The colour is brown/bay roan, unless modified by other colour modifying genes. It can only pass on allele Rn to its offspring.

Rn/Rn

E/E or E/e + a/a

Black Roan

Two copies of the dominant Rn allele. The colour is black roan, unless modified by other colour modifying genes. It can only pass on allele Rn to its offspring.

Rn/Rn*

e/e + A/A, A/a or a/a

Chestnut/sorrel Roan

One copy of the dominant Rn allele and one copy of the uncommon Rn* allele. The colour is chestnut/sorrel roan, unless modified by other colour modifying genes. It can pass on either allele Rn or Rn* to its offspring.

Rn/Rn*

E/E or E/e + A/A or A/a

Brown/bay Roan

One copy of the dominant Rn allele and one copy of the uncommon Rn* allele. The colour is brown/bay roan, unless modified by other colour modifying genes. It can pass on either allele Rn or Rn* to its offspring.

Rn/Rn*

E/E or E/e + a/a

Black Roan

One copy of the dominant Rn allele and one copy of the uncommon Rn* allele. The colour is black roan, unless modified by other colour modifying genes. It can pass on either allele Rn or Rn* to its offspring.

Rn*/Rn*

e/e + A/A, A/a or a/a

Chestnut/sorrel or Chestnut/sorrel Roan

Two copies of the uncommon Rn* allele. The colour can be chestnut/sorrel or chestnut/sorrel roan, unless modified by other colour modifying genes. It can only pass on allele Rn* to its offspring.

Rn*/Rn*

E/E or E/e + A/A or A/a

Brown/bay or Brown/bay Roan

Two copies of the uncommon Rn* allele. The colour can be brown/bay or brown/bay roan, unless modified by other colour modifying genes. It can only pass on allele Rn* to its offspring.

Rn*/Rn*

E/E or E/e + a/a

Black or Black Roan

Two copies of the uncommon Rn* allele. The colour can be black or black roan, unless modified by other colour modifying genes. It can only pass on allele Rn* to its offspring.

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P785 Coat Colour Sabino 1

Sabino is a general description for a group of similar white spotting patterns. The sabino pattern is described as irregular spotting usually on the legs, belly and face, often with roaning around the edges of the white markings. A mutation has been discovered that produces one type of sabino pattern, it has been named Sabino1 as it is not present in all sabino-patterned horses. More mutations will probably exist that account for other sabino patterns. The Coat Colour Sabino 1 test (P785) tests for the genetic status of the KIT gene. This gene has two variants (alleles). The allele SB1 is semi-dominant. One copy of the SB1 allele results in horses with broken Sabino markings and possibly only a small amount of white. Two copies of the SB1 allele result in at least 90% white, also referred to as Sabino-white. The allele N is recessive and does not have an effect on the basic colour.

The Coat Colour Sabino 1 test encloses the following results, in this scheme the results of the Coat Colour Sabino 1 test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Sabino 1

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Not Sabino 1. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Not Sabino 1. The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Not Sabino 1. The basic colour is not black modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/SB1

e/e + A/A, A/a or a/a

 

Chestnut/sorrel sabino

Sabino 1 pattern. One copy of the SB1 allele. Horse typically may have 2 or more white legs, blaze, spots or roaning in the midsection and jagged margins around white areas unless modified by other colour modifying genes. It can pass on either allele N or SB1 to its offspring.

N/SB1

E/E or E/e + A/A or A/a

Brown/bay sabino

Sabino 1 pattern. One copy of the SB1 allele. Horse typically may have 2 or more white legs, blaze, spots or roaning in the midsection and jagged margins around white areas unless modified by other colour modifying genes. It can pass on either allele N or SB1 to its offspring.

N/SB1

E/E or E/e + a/a

Black sabino

Sabino 1 pattern. One copy of the SB1 allele. Horse typically may have 2 or more white legs, blaze, spots or roaning in the midsection and jagged margins around white areas unless modified by other colour modifying genes. It can pass on either allele N or SB1 to its offspring.

SB1/SB1

e/e + A/A, A/a or a/a

 

Chestnut/sorrel sabino

Sabino 1 pattern. Two copies of the SB1 allele. Horse is complete or nearly complete white unless modified by other colour modifying genes. It can only pass on allele SB1 to its offspring.

SB1/SB1

E/E or E/e + A/A or A/a

Brown/bay sabino

Sabino 1 pattern. Two copies of the SB1 allele. Horse is complete or nearly complete white unless modified by other colour modifying genes. It can only pass on allele SB1 to its offspring.

SB1/SB1

E/E or E/e + a/a

Black sabino

Sabino 1 pattern. Two copies of the SB1 allele. Horse is complete or nearly complete white unless modified by other colour modifying genes. It can only pass on allele SB1 to its offspring.

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P807 Coat Colour Grey

A horse that inherits a Grey coat colour can be born in any colour. The grey gene causes progressive depigmentation (fading) of the hair and is considered to be the “strongest” of all coat colour modifying genes. The depigmentation process may last for years, but once the hair is depigmented, the original colour will never return. Some grey horses become completely white whereas others will keep tiny non-faded spots (also called fleabites). A horse can also carry mutations for other modifying genes which can further affect its coat colour.

The Coat Colour Grey test (P807) tests for the genetic status of the STX17 gene. This gene has two variants (alleles). The dominant allele G results in the Grey coat colour and the recessive allele N does not have an effect on the basic colour. The dominant allele G has a duplication of a part of the DNA. The test does not discriminate between horses carrying 1 or 2 copies of  the duplication (N/G or G/G). All horses carrying the duplication will turn grey.

The Coat Colour Grey test encloses the following results, in this scheme the results of the Coat Colour Grey test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Grey

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

Horse will not turn grey. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Horse will not turn grey. The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Horse will not turn grey. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/G or G/G

e/e + A/A, A/a or a/a

 

Grey (born chestnut/sorrel)

Horse is born with basic colour chestnut/sorrel (unless modified by other colour modifying genes) and will turn grey. One copy or two copies of the G allele. It can pass on either allele N or G to its offspring.

N/G or G/G

E/E or E/e + A/A or A/a

Grey (born bay/brown)

Horse is born with basic colour bay/brown (unless modified by other colour modifying genes) and will turn grey. One copy or two copies of the G allele. It can pass on either allele N or G to its offspring.

N/G or G/G

E/E or E/e + a/a

Grey (born black)

Horse is born with basic colour black (unless modified by other colour modifying genes) and will turn grey. One copy or two copies of the G allele. It can pass on either allele N or G to its offspring.

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P902 Coat Colour Overo-factor (OLWS)

The Overo coat pattern is a white spotting pattern with white patches on the side with a “frame” of colour surrounding the white. A horse can also carry mutations for other modifying genes which can further affect its coat colour. While Overo coloured horses are desirable, the mutation that causes the overo colour is linked to a fatal condition known as Overo Lethal White Syndrome or OLWS. A foal with OLWS is born all- white and dies of complications from intestinal tract abnormalities. The Coat Colour Overo test (P902) tests for a genetic factor that affects the function of the EDNRB gene. This gene has two variants (alleles). The allele O is semi-dominant. One copy of the O allele results in horses with overo coat pattern. Two copies of the O allele result in a lethal white foal (OLWS). The allele N is recessive and does not have an effect on the basic colour.

The Coat Colour Overo-factor test encloses the following results, in this scheme the results of the Coat Colour Overo-factor test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Overo-factor

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Not Overo. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Not Overo. The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Not Overo. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/O

e/e + A/A, A/a or a/a

 

Chestnut/sorrel overo

Overo pattern. One copy of the O allele. The horse has the desirable frame overo pattern unless modified by other colour modifying genes. It can pass on either allele N or O to its offspring.

N/O

E/E or E/e + A/A or A/a

Brown/bay overo

Overo pattern. One copy of the O allele. The horse has the desirable frame overo pattern unless modified by other colour modifying genes. It can pass on either allele N or O to its offspring.

N/O

E/E or E/e + a/a

Black overo

Overo pattern. One copy of the O allele. The horse has the desirable frame overo pattern unless modified by other colour modifying genes. It can pass on either allele N or O to its offspring.

O/O

Any result

Lethal (OLWS)

Foal with Overo Lethal White Syndrome (OLWS), lethal.

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P903 Coat Colour Tobiano

The Tobiano coat pattern usually involves white on all four legs below the hocks and knees and rounded white spots on the body with sharp, clean edges. The head is dark, with white markings like those of a solid colored horse. The white on the body will generally cross the top-line of the horse. The skin underlying the white spots is pink and under the colored areas it is black. The eyes are usually brown, but one or both may be blue or partially blue. The tail can be two colors, a characteristic seldom seen in horses that are not tobiano. A horse can also carry mutations for other modifying genes which can further affect its coat colour.

The Coat Colour Tobiano test (P903) tests for a genetic factor that affects the function of the KIT gene. This gene has two variants (alleles). The dominant allele TO results in the Tobiano pattern and the recessive allele N does not have an effect on the basic colour.

The Coat Colour Tobiano test encloses the following results, in this scheme the results of the Coat Colour Tobiano test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):

Result Tobiano

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Not Tobiano. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + A/A or A/a

Bay, Brown

Not Tobiano. The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

E/E or E/e + a/a

Black

Not Tobiano. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/TO

e/e + A/A, A/a or a/a

 

Chestnut/sorrel tobiano

One copy of the dominant TO allele. The colour is chestnut/sorrel tobiano unless modified by other colour modifying genes. It can pass on either allele N or TO to its offspring.

N/TO

E/E or E/e + A/A or A/a

Bay/brown tobiano

One copy of the dominant TO allele. The colour is bay/brown tobiano unless modified by other colour modifying genes. It can pass on either allele N or TO to its offspring.

N/TO

E/E or E/e + a/a

Black tobiano

One copy of the dominant TO allele. The colour is black tobiano unless modified by other colour modifying genes. It can pass on either allele N or TO to its offspring.

TO/TO

e/e + A/A, A/a or a/a

 

Chestnut/sorrel tobiano

Two copies of the dominant TO allele. The colour is chestnut/sorrel tobiano unless modified by other colour modifying genes. It can only pass on allele TO to its offspring.

TO/TO

E/E or E/e + A/A or A/a

Bay/brown tobiano

Two copies of the dominant TO allele. The colour is bay/brown tobiano unless modified by other colour modifying genes. It can only pass on allele TO to its offspring.

TO/TO

E/E or E/e + a/a

Black tobiano

Two copies of the dominant TO allele. The colour is black tobiano unless modified by other colour modifying genes. It can only pass on allele TO to its offspring.

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P305 Coat Colour Appaloosa Pattern-1 (PATN1)

The Appaloosa spotting pattern, also known as Leopard Complex spotting (LP) includes a highly variable group of white spotting- or depigmentation patterns in horses. Appaloosa horses have three additional identifiable characteristics: mottled skin around the muzzle, anus and genitalia, striped hooves and white sclera round the eyes. LP is the result of an incompletely dominant mutation in the TRPM1 gene, also known as the LP gene. The LP gene allows for the expression of the various leopard complex spotting patterns while other genes determine the extent (or amount) of white. One of the genes that is associated with increased amount of white in in LP horses has been identified (RFWD3) and has been termed Pattern-1 (PATN1) for first pattern gene. The Coat Colour Appaloosa Pattern-1 (PATN1) test (P305) tests for the status of the PATN1 gene. This gene has two variants (alleles). The dominant allele PATN1 results in an increased amount of white in horses that carry at least one copy of the LP allele on the LP gene. The recessive allele N does not have an effect on the basic colour. Horses that have one copy of the LP allele, in combination with at least one copy of the PATN1 allele most often have a Leopard or a near Leopard pattern. Horses that have two copies of the LP allele in combination with at least one copy of the PATN1 allele most often have a Few-spot or near Few spot pattern. Horses that have at least one copy of the  PATN1 allele but do not have a copy of the LP allele will not have a Appaloosa spotting pattern but can pass on the PATN1 allele to their offspring.

The Coat Colour Appaloosa Pattern-1 (PATN1) test encloses the following results, in this scheme the results of the Coat Colour Appaloosa Pattern-1 (PATN1) test are shown in combination with the possible results for the LP Gene (VHLGenetics does not yet offer a test for the LP gene).

Result PATN1

Result LP

Coat Colour

Description

N/N

N/N

No Appaloosa

The basic colour is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring.

N/N

N/LP

Blanket appaloosa

It can only pass on allele N to its offspring.

N/N

LP/LP

Snow cap appaloosa

It can only pass on allele N to its offspring.

N/PATN1

N/N

No Appaloosa

The basic colour is not modified unless modified by other colour modifying genes. It can pass on either allele N or PATN1 to its offspring.

N/PATN1

N/LP

Leopard or a near Leopard pattern

It can pass on either allele N or PATN1 to its offspring.

N/PATN1

LP/LP

Few-spot or near Few spot pattern.

It can pass on either allele N or PATN1 to its offspring.

PATN1/PATN1

N/N

No Appaloosa

The basic colour is not modified unless modified by other colour modifying genes. It can only pass on allele PATN1 to its offspring.

PATN1/PATN1

N/LP

Leopard or a near Leopard pattern

It can only pass on allele PATN1 to its offspring.

PATN1/PATN1

LP/LP

Few-spot or near Few spot pattern

It can only pass on allele PATN1 to its offspring.

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Date: 5th January 2017, version 4