The Pearl Gene
Pearl is a coat dilution modifier. It is one of the most recent equine colour genes to be mapped for commercial genetic testing. ‘Pearl’ is generally considered to be one of the most rare of colour traits.
The Pearl Gene is a recessive, cream-activated, dilution gene. Recessive means that one copy of the gene in a horse has no expression (it is "invisible"), and two copies (homozygosity) results in full expression.
Cream-activated means that it also reacts with cream: it shows up, adding another instance of dilution if there is a cream gene present. In this case it manifests as a "double dilution”: pearl and cream.
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.