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. |
