Roan (horse)
The silvering effect of mixed white and colored hairs can create coats that look bluish or pinkish.
Horses with the roan pattern have an even mixture of white and colored hairs in the coat.
[1] These interspersed white hairs are more scattered or absent on the horse's head, mane, tail, and lower legs.
[1] The unaffected color on the legs often forms a sharp, inverted "V" above the knee and hock, not seen in other roan-like coat patterns.
[6] While roan is always present at birth, the soft first coat of newborn foals may not show the white hairs well.
If the skin is damaged by even a very minor scrape, cut, or brand, the coat grows back in solid-colored without any white hairs.
[6] In the most general sense, the word "roan" refers to any animal with a mixture of white and colored hairs in the coat.
[1][6] In studies of the white patterning genotypes of laboratory mice, no fewer than four produced roaning or flecking.
[14] Like other dun coat colors, grullos have dark or black primitive markings, always including a stripe down the back.
[6] Rabicano roaning frequently forms rings of white hair around the base of the tail, and in extensively roaned rabicanos, the white hairs may converge to form vertical stripes over the ribcage.
[22] A small number of Thoroughbred offspring of the brindle-patterned stallion Catch A Bird phenotypically appear to be true roan, and though few of those reproduced, some offspring of his daughter Slip Catch, though registered as bay, have apparently been verified as carrying the roan gene.
[23] [24] Nonetheless, most Thoroughbreds and Arabians with roan-like coats are most likely related to graying or rabicano characteristics.
[25][26] Thoroughbred "roans" are described by the Jockey Club as a mixture of white with red or brown hairs, but which researchers identify as chestnuts turning gray.
[11][25] The Arabian Horse Association defines "roan" as an even mixture of white and colored, usually chestnut, hairs, but researchers suggest most animals so classified are probably either rabicano, or have a partially-spotted pattern that results from a dominant white allele.
[1] Traits that are dominantly inherited cannot skip generations, meaning that two nonroan parents cannot produce a roan offspring.
The University of California, Davis School of Veterinary Medicine's genetics services has developed a DNA test that uses genetic markers to indirectly determine the number of Rn or rn alleles a horse has.
[1] The mutation responsible for true roan has not yet been identified exactly, but been assigned to equine chromosome 3 (ECA3) in the KIT sequence.
A 1979 study of American-bred Belgian draft horses found fewer roan offspring from roan-to-roan matings than expected for a simple dominant trait.
[27] Genetic science in the 1970s could not provide a clear answer, as methods of molecular analysis had not yet been developed.
[31] In 1982, a linkage grouping was proposed, including three genes for serum proteins, and three for coat color: tobiano spotting, chestnut, and roan.
Normally, the chestnut and roan alleles would be separated during chromosomal crossover, but these two linked genes usually remain together.
