Roan is a horse coat color pattern characterized by an even mixture of colored and white hairs on the body, while the head and "points"— lower legs, mane and tail — are mostly solid-colored. Horses with roan coats have white hairs evenly intermingled throughout any other color. The head, legs, mane and tail have fewer scattered white hairs or none at all. The roan pattern is dominantly-inherited, and is found in many horse breeds. True roan is always present at birth, though it may be hard to see until after the foal reaches adulthood.
Roan is a simple dominant trait symbolized by the Rn allele. Traits that are dominantly-inherited cannot skip generations, meaning that two non-roan parents cannot produce a roan offspring.
Homozygous vs Heterozygous
A homozygous roan horse carries two Rn alleles: RN/RN, while a heterozygous horse carries one: RN/n. Both homozygous and heterozygous roan horses are identical in appearance. The only difference is that a homozygous horse will have offspring that will be 100% roan as well, while a heterozygous horse could have non-roan offspring. To illustrate:
- Breeding a RN/RN stallion to a non-roan mare (rn/rn or n/n in game) will produce 100% roan (RN/n) offspring.
- Breeding a RN/n stallion to a RN/n mare will produce 25% homozygous roan (RN/RN), 50% heterozygous roan (RN/n), and 25% non-roan (n/n) offspring. This means there is a very high possibility for breeding a roan offspring but there is also a slight chance that the foal is non-roan.
- Breeding a RN/n stallion to a non-roan (n/n) mare will produce 50% Roan (RN/n) offspring.