Pearl, also known as "Barlink Factor" in Quarter and Paint horses, is one of the dilutions present in horses.
¶ Phenotype
Pearl lightens the coat, mane and tail. The skin is pink and/or mottled and the eyes are amber-coloured.
Pearl horses can in some cases look almost identical to champagne horses: both have freckles/mottled skin, amber eyes, pinkish skin, and their coat colours can look very similar. Therefore, gene testing is very important.
| Pearl - Irish Cob Horse | |
| Example | Information |
|
Chestnut pearl Pearl on a chestnut base results in a pale, uniform apricot colour of the body, mane and tail. |
|
Bay pearl Pearl on a bay base results in an apricot-coloured body similar to chestnut pearl, but with darker brown points. |
|
Black pearl Black horses with pearl have a tan body with darker points. |
¶ Genotype
The pearl (prl) dilution is an allele of the MATP gene (also known as SLC45A2) on horse chromosome 21. Pearl has only recently been discovered, but the mutation is thought to be quite old. The pearl mutation is thought to disrupt the transport of pigment molecules to melanocytes (pigment cells), resulting in the dilution.
Pearl is recessive, which means that a horse will need 2 copies for the coat to be diluted; although horses heterozygous for pearl may have slightly lighter skin and/or small pale spots. When a horse has one copy of pearl, this can be referred to as a “pearl carrier”. In Horse Reality, pearl carriers won't look any different, but they can pass on the prl-allele to their foals. Below, the resulting phenotype of each genotype is listed:
- prl/prl = Pearl
- prl/n = Not pearl (pearl carrier)
- n/n = Not pearl
The presence of the pearl allele can be tested at the Laboratory.
Another allele that can be found on the same gene as cream, is the cream (CR) dilution. Since they share a locus, horses can be homozygous for either pearl or cream separately, but not for both at the same time. They can, however, be heterozygous for both, and pass one of the two alleles on to a foal. Pearl also interacts with the CR-allele to create cream pearl "pseudo-double dilutes". Below, the resulting phenotype of each genotype is listed:
- CR/prl = Cream pearl
- CR/CR = Homozygous cream
- CR/n = Heterozygous cream
¶ Breeds
The pearl dilution is quite rare and probably originated in Iberian breeds. The “Barlink Factor” dilution first found in the Paint Horse stallion Barlink Macho Man, was at first thought to be a separate mutation but is also caused by pearl. The presence of pearl in Quarter Horses and Paint Horses likely reflects an Iberian ancestry. The following table lists all breeds that can currently have the pearl (prl) allele in-game.
| Breeds |
| Akhal-Teke Horse |
| Arabian Horse |
| Brabant Horse |
| Brumby Horse |
| Camargue Horse |
| Cleveland Bay |
| Exmoor Horse |
| Finnhorse |
| Fjord Horse |
| Friesian Horse |
| Haflinger Horse |
| Icelandic Horse |
| Irish Cob Horse |
| Kladruber Horse |
| Knabstrupper |
| Lipizzaner |
| Lusitano |
| Mongolian Horse |
| Mustang Horse |
| Namib Desert Horse |
| Noriker Horse |
| Norman Cob |
| Oldenburg Horse |
| Pantaneiro Horse |
| Pura Raza Española |
| Quarter Horse |
| Shetland Pony |
| Shire Horse |
| Suffolk Punch |
| Thoroughbred |
| Trakehner Horse |
| Welsh Pony |
¶ References
- Bellone R., Sponenberg D. P., Equine Color Genetics, 4th Edition, 2017, Wiley-Blackwell
- UC Davis Veterinary Genetics Laboratory; https://vgl.ucdavis.edu/test/pearl; Access: December 2022
- Avian Animal Genetics; https://avian2.animalgenetics.com/Equine/Coat_Color/Pearl.asp; Access: December 2022
- Sevane N. et al, Explicit evidence for a missense mutation in exon 4 of SLC45A2 gene causing the pearl coat dilution in horses, Animal Genetics, 2019