Independent of what a horse looks like, there are only two base colors of horses – red and black. From there, horses layer modifiers and dilutions and then add, over that, patterns made up of white hairs that are base hairs without any pigment. Over the modifiers, dilutions and patterns, if a horse has the gene for graying as they age, they will eventually turn gray.
The gene that determines whether a horse is red or black is known as the Black Factor and the abbreviation “E.” It is a dominant determinant, so if a horse has an E from each parent, it will be EE and black. The recessive Black Factor is noted as “e.” Because of dominance, if only one parent contributes an “E” while the other contributes an “e,” the result is still a black base color in the foal. However, if both parents contribute the recessive Black Factor “e,” so the foal’s Black Factor gene combination is “ee,” there will not be a black foal. Instead, the foal with an “ee” has a base color of red.
EE or Ee foals will have a base of black. ee foals will have a base coat of red which we call chestnut or sorrel, depending on breed and upbringing. But genetically, a chestnut and sorrel are the same.
- If you breed an EE to an EE, an EE to an Ee, or an EE to an ee, 100% of the foals will be black. The resulting pairs will be one of the following: EE, Ee and eE. Each pair will have a dominant E yielding a 100% black base.
- If you breed an Ee to an Ee, 75% will be black and 25% red. The resulting pairs will be one of the following: EE, Ee, eE and ee. 3 out of 4 possible results have a dominant E, while 1 out of 4 has no dominant E.
- If you breed an Ee to an ee, 50% of the foals will be black, and 50% will be red. The resulting pairs will be one of the following: Ee and ee. 2 out of 4 possible results have a dominant E, while 2 out of 4 have no dominant E.
- If you breed an ee to an ee, 100% will be red. The resulting pairs will all be ee with no dominant E.
All horses on the planet are either black or red, but other dominant genes modify this creating the bay and the gray. Further dilution of these colors by additional genes produces different shades, such as palomino and cremello. Expressive genes will add markings, such as face markings, spots, dorsal stripes and white body markings. However, they all are on top of the base colors.
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