The Pearl allele is the newest dilute discovered however is suspected to be around for hundreds of years at least. The Pearl allele is the only recessive dilute gene discovered so far which is why it was so illusive to be genetically studied and discovered. Even now the colour is so rare that horses carrying two alleles of the Pearl dilution, thus showing the affect of the Pearl dilution, are often mistaken for something else such as Champagne or completely regarded as a mystery colour. As of right now there are no ‘true’ names for the colours the Pearl allele results in, most often heterozygous horses are called Pearl carriers (such as ‘Black Pearl carrier’) and homozygous horses are simply referred to as Pearl (such as ‘Black Pearl’). I will be using those terms when talking about the colours. The only true name for a Pearl dilute horse that is catching on for the Chestnut Pearl which is being called Apricot. Currently the gene is present in Spanish breeds, American stock horses (which old lines trace back to Spanish breeds) and the Gypsy Vanner.
Pearl Allele Genetics
The Pearl allele is located at the same locus the Cream allele is, which is at the MATP locus. Genetic testing is available to the public. When writing out the Pearl allele in a genome it is shown as a Pr. Pearl is recessive; this means both parents must be a Pearl carrier in order to have a chance to produce a Pearl offspring. This also means that you could breed together two normal looking horses and have a surprise on foaling day with a uniquely coloured Pearl foal.
The Pearl allele is a dilute gene that affects the horses coat, skin and eyes. Homozygous Pearl horses have a purple hue to their skin and will often have some subtle mottling on the skin. The eyes are usually born blue but turn to hazel and light brown over time. Depending on the base coat the Homozygous Pearl will lighten the red pigment to a golden tan or apricot colour (hence the name catching on for Chestnut Pearls) and will lighten black to a chocolate or slate brown. There is also a sheen to the Homozygous Pearl coat. Some people claim that Heterozygous Pearls have lighter skin then horses without the Pearl allele and others go so far to claim there is a difference in coat and sheen when there is a Pearl allele present. When looking at pictures it is too hard for me to see if these claims are true.
Basic Pearl Colours
Below is a chart to help show what the basic colours of the Pearl allele are. A basic Pearl colour is when the Pearl allele is combined with Extension and Agouti colours. On the left we see those basic Extension and Agouti colours and on the right we see what those colours are when the Pearl allele is present. As you can see the Pearl allele is very rare and only a few combinations with the base colours have been documented, hopefully in the future breeders will be experimenting bringing new colours to the world!