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. |
