Pearl (PRL)
Gene or Region: MATP / SLC45A2
Reference Variant: G (N)
Mutant Variant: A (prl)
Affected Breeds: Spanish Origin
Research Confidence: High Confidence - similar dilutions reproduced in other species
Explanation of Results: prl/prl = homozygous for Pearl, trait expressed prl/n = heterozygous for Pearl, no trait expressed n/n = no variant detected
General Description for Pearl
Prl is an example of a recessive trait – two copies are needed to see an affect. While a single prl allele does not affect the coat color, some horses show skin lightening/freckling. Prl homozygotes (prl/prl) are visually similar to horses with the champagne dilution, displaying diluted hair, skin, and eye color. A horse with one CR and one prl allele is known as a compound heterozygote, and appears similar to double cream or cream plus champagne dilutions.
Genotype and Phenotype
Black with single pearl (E/_ a/a prl/N): Black or Black Pearl Black with double pearl (E/_ a/a prl/prl): Classic Pearl Black with one cream one pearl (E/_ a/a CR/prl): Smoky Black Pearl
Bay with single pearl (E/_ A/_ prl/N): Bay or Bay Pearl Bay with double pearl (E/_ A/_ prl/prl): Amber Pearl Bay with one cream one pearl (E/_ A/_ CR/prl): Buckskin Pearl
Chestnut with single pearl (e/e prl/N): Chestnut or Chestnut Pearl Chestnut with double pearl (e/e prl/prl): Gold Pearl Chestnut with one cream one pearl (e/e CR/prl): Palomino Pearl
*Other dilutions, modifiers, and spotting genes can further alter the color of a horse – for simplicity, we have not named all possible combinations! *Unlike most equine coat colors, pearl does not currently have a commonly used set of names. Pearl horses are often registered as the corresponding champagne or cream coat colors.
Gene Information
_SLC45A2 _is a transporter protein involved in pigment synthesis. Mutations in this gene have been well documented to result in a variety of dilution and albino coat colors in many species. Both mutations are single base substitutions that change an amino acid, and thus likely alter the function of the encoded protein.
References
Mariat D et al., “A mutation in the MATP gene causes the cream coat colour in the horse.” (2003) Genet Sel Evol. 35: 119-33.
Bailey E & Brooks S. “Color Diluting Genes.” (2013) Horse Genetics, CABI International, Boston, MA, 42-52.
Stamatelakys I. “Precious Pearls” (2009) Paint Horse Journal. May 2009, 76-83.
More Horse Color Genetics
Dominant White 19
Dominant White 19 (W19) is found in Arabian horses and may result in a bald face with extended white on legs and belly spots for heterozygotes (W19/n). Homozygotes are reported to be nearly completely white with varying degrees of congenital birth defects and it is estimated that combinations of W19/W19 and other W19/X combinations may be largely lethal.