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. |
