Roan, like grey, is a pattern gene which sprinkles white hair over an otherwise normally pigmented animal. However, the pattern of white hair, the progression with age and the response to scarring are quite different from grey.
It should be pointed out that horsemen use the word “roan” quite loosely. In Thoroughbreds, for instance, it is used as a synonym for grey, particularly rose grey. There are several forms of roan covered by this loose usage, but the one discussed here is classic roan, which is due to the dominant roan gene. Frosty roan, varnish roan, roaned, rabicano and the roaning caused by some white spotting patterns will be discussed separately.
In classic roan the head, legs, mane and tail remain fully pigmented but there is an admixture of white hairs on the body of the horse. Foals are born roan or shed their foal coat to roan, and beyond that point the roan pattern is not progressive with age. In fact, roans may darken with age. They may also change appearance with season, appearing lightest when the coat is shortest and darker in winter coat.
Corn marks (flecks of the base color) are common on roans, and scars often lack roaning. Photographs of wild horses often show this to an extreme, as dominance battles frequently leave extensive scars.
Roan is due to a dominant gene. At one time, the gene was thought to be a lethal when two roan alleles were present at the roan locus, but more recent work has shown this not to be true. The gene itself has not been found, but it is known to be near, if not part of, the KIT locus on equine chromosome 3. There is clear linkage with chestnut at the extension locus, and tobiano is also linked. As an example of this, if a bay roan is bred to a chestnut, most of the foals will be bay roans or chestnuts, with only a few being chestnut roan or bay. Linked genes do not follow the rules of totally independent inheritance. A linkage test for roan is available if you want to know if a roan is homozygous.
Roan is quite variable in its intensity. Now and then a roan foal comes from two parents thought not to be roans, but close examination of the parents generally shows one to be a roan with very little roaning.
Roan may occur on any base color with any combination of diluting genes and marking genes. Black roans are often referred to as blue roans, bay roans as red roans, and chestnut roans as strawberry roans, but there are also references to purple roans, lilac roans, and honey roans. Further, a “red roan” could have either bay or chestnut as the underlying color, while some dark bay roans were called blue roan or purple roan. The modern practice is to put the base color first, followed by “roan.”
Roi (in Homecoming) will someday get a palomino roan mare with leopard (Appaloosa) markings—a horse overlooked by others because of her color but in fact quite a good horse. She is also a good example of the way different color genes can combine.
(The 3 photos on the left were taken at my cousin’s horse farm in Alabama.)