The pearl mutation dilutes both red and black pigment if two copies are present
Breeds known to carry this mutation
Quarter Horses and related breeds, Paint Horses, and Spanish breeds such as Andalusian and Lusitanos
Pearl is a rare dilution usually only observed in Quarter horses and Spanish horse breeds. This mutation is recessive so the horse must have two copies to express the effect. Horses carrying two copies of pearl (Prl/Prl) will have a lightened coat, mane, and tail, in addition to bright eye colours. Pearl also interacts with Cream dilution to produce pseudo-double cream dilute phenotypes. This is because the Pearl mutation is found in the same gene as Cream dilution.
Interpretation of results
n/n: Horse does not carry the pearl dilution allele.
n/Prl: Horse is heterozygous for the pearl dilution allele. The horse will not have a diluted coat but has a 50% chance of passing on pearl to its offspring.
Prl/Prl: Horse has two copies of the pearl dilution allele. It will have a diluted coat and will pass the pearl gene onto all its offspring.
Holl et al. A candidate gene approach identifies variants in SLC45A2 that explain dilute phenotypes, pearl and sunshine, in compound heterozygote horses. Animal Genetics 2019; 50:271-4. doi: 10.1111/age.12790