Coat formed by the combined effect of Gray and Roan on the Chestnut base.
Typical Genetic Formula
e/e G/n Rn/n
Possible Genotype Variations
e/e A/A G/n Rn/n
e/e A/A G/n Rn/Rn
e/e A/A G/G Rn/n
e/e A/A G/G Rn/Rn
e/e A/a G/n Rn/n
e/e A/a G/n Rn/Rn
e/e A/a G/G Rn/n
e/e A/a G/G Rn/Rn
e/e a/a G/n Rn/n
e/e a/a G/n Rn/Rn
e/e a/a G/G Rn/n
e/e a/a G/G Rn/Rn
The Genetic Basis
For a horse to be born Gray Roan Chestnut, it must receive the following combination from its parents:
- To have the red base (Chestnut), this animal necessarily inherited a recessive (e) allele from the sire and another from the dam. Both parents carried the red factor.
- Since the Roan gene is dominant, at least one parent was necessarily Roan (Rn).
- Gray does not skip generations. For this animal to be Gray, the sire or dam had to be Gray to provide the (Rn).
Understanding the Alleles
The horse Gray Roan Chestnut has a specific combination of alleles. Below, we explain each genetic component that forms this coat:
- e/e (Red Factor): The animal has a fundamentally red base (Chestnut), due to the total absence of black pigment.
- A/ (Agouti): The Agouti gene, when active (with E present), restricts black pigment to the extremities. Carried with no visual effect in e/e animals.
- a/a (Non-Agouti): Allows black to spread over the entire body when combined with E. In e/e animals it is invisible but still passed on.
- G/ (Grey): Progressive graying. Epistatic — covers all other colors.
- Rn/ (Roan): aaaaaaaaaaaaaaaa
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