There is only one form of Sabino that can be tested for, SB1, but many horses that exhibit phenotypical sabino markings test negative for SB1. It is not known at this time how many different genes may be expressing as what we call sabino. Sabino tends to affect the back legs of the horse first. It tends to leave chin white, and roaning along the edges of white markings, and sometimes scattered in the coat. Like any pattern, expression varies. At times markings as small as a star are blamed on sabino, although in truth it is difficult or impossible to tell what pattern a very minimal horse carries without testing. According to the current visual evidence, sabino does not cause blue eyes. Sabino, at least SB1, is an incomplete dominant, meaning that homozygous horses express much more white then heterozygous horses - hence the term "max white sabino". The only breed currently thought to lack sabino is the Icelandic Horse. Many of the horses formally labeled Sabino that have tested negative for SB1 are now being tested for W20.