Our latest monthly mystery horse is a gorgeous part-bred Arab/TB called Tanlee Romeo. He has a chocolate coat that is lighter than most smokey blacks (black buckskins) but more evenly coloured that most dark buckskins. He also has a very large blaze, four high socks and a white tail tip. White markings on the end of the tail are often a sign that splashed white is present, but splashed white is extremely rare in the Arabian and Thoroughbred breeds. Tanlee Romeo’s eyes are brown.
Romeo’s dam is dark brown or black with a narrow blaze and four socks to the fetlocks, while his sire is a cremello. We picked Romeo because of his interesting coat colour and large white markings. We tested him for agouti, red/black, cream, silver and dun/d1 to figure out his coat colour. We also tested for W20, SW1 and frame overo (just in case!) to see if we could find the cause of his white markings.
Romeo has a black base coat colour: E e (one copy red, one copy black) for red/black, and a a (two copies non-bay) for agouti. He has one copy of cream, and one copy of d1 (nd1). He was negative for silver. These results show that Romeo is a smokey black with d1 (nd1). Here in Australia smokey blacks are also called black buckskins.
Have a look at our previous posts on d1 (nd1) for examples of how it can lighten coat colour.
The only white marking gene that we got a positive result for was W20. Romeo has one copy of W20. The SW1 test was negative, and as expected the frame overo test was too. (SW2 and SW3 are not relevant because they are only found in particular Paint horse bloodlines.)
For Arabians and Thoroughbreds one copy of W20 usually causes white markings like those seen on his dam in the foal pics here. It is possible that W20 is interacting with an unknown white marking gene to produce the large markings and white tail tip we see on Romeo.