Equine Color Genetics
Equine color genetics is one of the most fascinating areas in the field. Horses can come in more color variations that almost any other species on the planet. Those variations in color all come down to what genes are inherited from the horse's sire and dam. The apple really doesn't fall that far from the tree!
Concept #1: Base Color
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.
Concept #2: Dilution
The rest of the color genes act as modifers on the base coat. These modifers include cream, pearl, champagne, silver, and dun. These dilutions do not all act in the same manner and some have no effect on red pigment, much like the Agouti gene. These dilutions are what provide us with palominos, buckskins, duns, cremellos, etc.
Concept #3: Patterns
The pattern genes are also color modifiers, but instead of diluting, they delete the color altogether. The pattern genes include frame overo, splashed white overo, sabino, tobiano, and appaloosa. The grey gene is also included in this, although it acts differently in that color is deleted over time.
This is a modified chart based on that found on UC Davis' website (click here). It shows the required genotype for each phenotype. Some traits (such as grey) override all others, making it unnecessary to list other alleles.