Pearl is a coat dilution modifier. The pearl dilution is one of the most recent equine color genes to be mapped for commercial genetic testing. It has only been confirmed in a few breeds and is generally considered to be one of the rarest of the color traits. The presence of the pearl gene has been confirmed in breeds of Iberian origin, such as the Lusitano and Purebred Spanish horse. It is also theorized to be present in the Spanish Mustang. When found in the American Quarter horse, the pearl dilution is regularly referred to as the 'Barlink Factor'.
The pearl dilution is a recessive gene. Generally, this means that a horse requires two copies of a gene in order for it to be expressed. However, the pearl dilution can appear under two circumstances:
- Two inherited copies of the gene are present (c/c). Horses carrying two copies of pearl will have a lightened coat, mane and tail. They will also have bright eye colors due to pigment changes caused by the gene.
- The cream dilution gene is also present in the pearl-carrying horse (C/C or C/c in a P/p or p/p horse). It has been confirmed that the dominant cream gene will activate the pearl phenotype if the two genes are present. Horses positive for both cream and pearl will exhibit a double-dilute phenotype. They will also have a pale coat color similar to that of horses that are homozygous (having two copies – C/C) for the cream gene.
The pearl dilution will not be seen if a horse is heterozygous for the trait (P/p) and negative for the cream (c/c) dilution gene. A single inherited copy of the pearl gene alone will not affect the carrier's phenotype. Heterozygous pearl horses may breed diluted offspring if bred to another pearl carrier or a cream dilute horse. The visual coat color changes caused by pearl dilution are dependent upon the foundation color of the horse. For example, the phenotype of a double-pearl bay (having two copies of pearl) will vary from the phenotype of a double pearl chestnut.
|Homozygous: Horse has two copies of the Pearl Dilution gene mutation and will appear pearl. Horse will pass a copy of the gene on to all offspring.
|Heterozygous: Horse has one copy of the Pearl Dilution gene mutation. Horse will appear pearl if at least one copy of cream is present and can pass this gene on to any offspring.
|Negative: Horse is negative for Pearl Dilution.
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]