Horses all have a base color of either black, bay, or red - regardless if they are grey, buckskin, spotted, etc.

 

The base color is controlled by two genes - the Extension gene and the Agouti gene.

• The Extension gene controls the production of black or red pigment in the coat.

  • Represented by the letter "E" or "e"

  • Black is dominant, which means that only one copy of the dominant allele is needed to produce a black horse.
     

• The Agouti gene can then modify the black pigment by pushing it to the points - creating a bay horse.

  • Represented by the letter "A" or "a"

  • Agouti is dominant, which means that only one copy of the allele is needed to produce a bay horse.

  • Agouti is not seen physically on red horses.