We have one last example of a SB1 + W20 horse to share. This is Zips Stormy Showdown, a Paint horse colt.
Zips Stormy Showdown is a chestnut with both sabino 1 and W20, but no other known pattern genes. Just like Tahmathor Park Colonial Jasper and Yarreh Lane Flash Gentleman Jack, Showdown was born with substantial white markings but still quite a bit of colour along his topline.
Over his first year the white increased to the point where very little colour still remains. He is now a white horse with a handful of chestnut hairs in his tail.
The combination of sabino 1 and W20 produces a much, much more white than just sabino 1 by itself, or just W20 by itself. If you are curious as to exactly why this happens, read more about W20, sabino 1 and the other W genes here.
As a side note, any horse with the SB1/W20 genotype will pass on either SB1 (sabino 1) or W20 to its foals – never both, never neither.
Thank-you to Rik Brierly (FB) for sharing her colt’s photos and story.