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. |
