Pearl Dilution

Animal Genetics > Horse Tests > Equine Color Tests > Pearl Dilution
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Description

Pearl is a coat color dilution and one of the rarest equine color traits. It is caused by a variant in the SLC45A2 gene, the same gene responsible for Cream dilution. Pearl has been confirmed in breeds of Iberian origin such as the Lusitano and the Pura Raza Española (Purebred Spanish Horse), and is also found in the American Quarter Horse and Paint Horse, where it is often called the “Barlink Factor.” It is thought to be present in the Spanish Mustang as well.

Pearl is recessive, so a horse normally needs two copies for the dilution to show. However, because Pearl and Cream are variants of the same gene, the dilution can appear in two situations:

  1. Two copies of Pearl (Prl/Prl). The horse has a lightened coat, mane, and tail, with an apricot or pale golden cast, and often bright blue or amber eyes.
  2. One copy of Pearl with one copy of Cream (n/Prl with n/Cr). Cream and Pearl interact to produce a pseudo-double-dilute phenotype: a pale coat similar to a cremello or perlino, with pale skin and blue or green eyes.

A horse with one copy of Pearl and no Cream (n/Prl) shows no dilution and looks like a normal horse of its base color. These carriers can still produce diluted foals when bred to another Pearl carrier or to a Cream dilute horse.

The visible effect of Pearl depends on the horse’s base color, so a double-pearl bay looks different from a double-pearl chestnut. Because carriers are not identifiable by eye, DNA testing is the only way to confirm whether a horse carries Pearl.

Possible results

Genotype Description
Prl/Prl Homozygous: Horse has two copies of the Pearl Dilution variant and will appear pearl. Horse will pass one copy to all offspring.
n/Prl Heterozygous: Horse has one copy of the Pearl Dilution variant. The horse will appear pearl only if it also carries at least one copy of Cream; otherwise it shows no dilution. Each foal has a 50% chance of inheriting the Pearl variant.
n/n Negative: Horse does not carry the Pearl Dilution variant.

Breeds Affected

Lusitano, Pura Raza Española (Andalusian), American Quarter Horse, Paint Horse, Spanish Mustang, Peruvian Paso, Gypsy Vanner

Reference

Explicit evidence for a missense mutation in exon 4 of SLC45A2 gene causing the pearl coat dilution in horses.

Sevane N, Sanz CR, Dunner S.
Anim Genet. 2019 Jun;50(3):275-278. doi: 10.1111/age.12784. Epub 2019 Apr 10.
PMID: 30968968

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