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. |
