Horse colour - Pearl Dilution

Pearl Dilution

Pearl is a coat dilution modifier, one of the most recent equine colour genes to be mapped for commercial genetic testing, therefore as yet has only been confirmed in a few breeds and is generally considered to be one of the rarer of all colour 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 theorised to be present in the Spanish Mustang. Where found to be present in the American Quarter horse, Pearl dilution is regularly referred to as the 'Barlink Factor.'

Pearl dilution is a recessive gene, therefore will only take affect on the coat of the carrying horse if:

1) Two inherited copies of the gene are present. Specimens carrying two copies of Pearl will have a lightened coat, mane and tail, in addition to bright eye colours due to pigment changes caused by the gene.

2) The Cream Dilution gene is also present in the Pearl-carrying 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, again with a highly pale coat colour similar to that of horses that are homozygous for the Cream gene.

Pearl dilution will not act if a horse is Heterozygous for the trait, but negative for the Cream dilution gene, meaning that a single inherited copy of the Pearl gene, will alone 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 colour changes caused by Pearl Dilution are based upon the foundation colour of the horse, for example the phenotype of a double-pearl Bay, will vary from the phenotype of a double pearl Chestnut.

DNA testing is available for the Pearl gene, the results are designated as follows:

nn - Negative. horse can be considered a non-carrier of the Pearl gene.

nPrl - Heterozygous. Horse is positive for Pearl, having inherited the trait from one parent. No visual change to carrying horse, except for in the additional presence of the Cream Dilution gene. The horse will pass the Pearl dilution gene to approximately half of foals when bred.

PrlPrl - Homozygous. Horse is positive for Pearl, and carries two inherited copies of the gene. The phenotype of the Homozygous Pearl horse will be of dilute appearance, regardless of the presence of Cream Dilution. The Homozygous Pearl specimen will pass the Pearl gene to 100% of foals, but may only produce diluted offspring if bred to another Pearl or Cream carrier.