Did you know that nearly thirty different types of dominant white have been found in horses so far? They are all different mutations in one gene, called the KIT gene. Horses are unique among domesticated animals in having so many different variants of KIT. Other variants of the KIT gene in horses cause white markings: these are sabino 1 and W20.
W25 and W26 are two types of dominant white that have been recently identified in Australian Thoroughbreds. They are not widespread yet, but show similarities to the Airdrie Apache (W22) and Milady Fair/Colourful Gambler (W27) lines in terms of the amount of white they cause.
All of the dominant white genes interact with W20 and other white marking genes to produce more white. Horses with any form of dominant white plus the W20 gene are usually completely white. If you read the details about the W25 and W26 families, you can see examples of horses with frame overo and dominant white that are completely white too.
Over the next few weeks we will post a few examples showing how W20 can boost sabino 1 (another KIT gene variant) to produce horses that are 80-95% white.
Practical Horse Genetics is offering testing for these two new dominant white lines.