Welcome to part 2 of Equine Coat Color Genetics: Gray, Roan, and Dun
This blog builds on the information presented in the previous blog: Equine Coat Color Part 1. We recommend you read that post first to best understand this one.
The Gray Gene
We all know that gray horses aren’t born gray, but they are not all born black. A gray horse can start out any color at birth, and then they fade as they age, sometimes slowly, and sometimes rapidly. The ‘gray’ gene is simple. ‘G’ stands for ‘gray’, and ‘g’ for ‘NOT gray’.
GG = horse goes gray
Gg = horse goes gray
gg = horse stays whatever color it is at birth
The color that a gray horse is born with is determined by the other color genes. For example:
EE or Ee (black-based), with aa (unrestricted black), with GG or Gg (gray) = Horse born black, then goes gray.
EE or Ee, with AA or Aa (restricted black), with GG or Gg (gray) = Horse born bay, then goes gray.
ee (red-based) with GG or Gg (gray) = Horse born chestnut, then goes gray.
Roaning
The roan gene is a color modifier that causes an intermixing of white hairs with the base coat color, with more white over the neck and body and less white on the head and legs. Black based horses with roan have black and white hairs, and are called blue roans. Chestnut based horses with roan have red and white hairs, and are called red roans. Bay horses with roan have brown and white hairs, and are either called bay roans or strawberry roans.
The roan gene is a dominant trait, meaning that ‘Rn’ for ‘roan’ is dominant to ‘rn’ for ‘NOT roan’. The famous cutting horse mare Royal Blue Boon is an example of a blue roan, and her son, the famous sire Peptoboonsmal, is a red roan.
EE or Ee (black-based), with aa (unrestricted black), with RnRn or Rnrn = Blue Roan
EE or Ee (black-based), with AA or Aa (restricted black), with RnRn or Rnrn = Bay Roan
ee (red-based), with RnRn or Rnrn = Red Roan
Dun Dilution – Dun, Red Dun, and Grulla
The dun gene is a color dilution factor that causes a horse to have a diluted coat color, a dorsal stripe, and other ‘primitive’ markings, such as bars on the legs, and sometimes dark marks near the withers. The dun gene is responsible for grulla, dun, and red dun horses. Dun is a dominant trait. ‘D’ for ‘dun’ is dominant to ‘d’ for ‘NOT dun’. The other color genes determine what shade the base coat color is.
A grulla is a black horse with the dun dilution factor.
EE or Ee (black-based) with aa (unrestricted black) with dd (not dun) = Black.
EE or Ee (black-based) with aa (unrestricted black) with DD or Dd (dun) = Grulla.
A dun is a bay horse with the dun dilution factor.
EE or Ea (black-based), with AA or Aa (restricted black), with dd (not dun) = Bay.
EE or Ea (black-based), with AA or Aa (restricted black), with DD or Dd (dun) = Dun.
A red dun is a chestnut horse with the dun dilution factor.
ee (red-based), with dd (not dun) = Chestnut.
ee (red-based), with DD or Dd (dun) = Red Dun.
Look for the next installment of Equine Coat Color Genetics coming soon for info on Palomino, Buckskin, and Smokey Black!
