Horse coat color is determined by multiple genes working together. The two primary genes are Extension (E) and Agouti (A). The Extension gene controls whether a horse can produce black pigment, while the Agouti gene controls where black pigment is distributed on the body. These base colors can then be modified by additional genes like Cream, Gray, Dun, and various pattern genes.

The three base coat colors are Bay, Black, and Chestnut (also called Sorrel). Bay horses have a brown body with black points (mane, tail, and lower legs). Black horses are uniformly black. Chestnut horses are reddish-brown with a mane and tail the same color or lighter than their body.

The Cream gene dilutes red and black pigment. A single copy (heterozygous) creates colors like Palomino (on chestnut), Buckskin (on bay), and Smoky Black (on black). Two copies (homozygous) create double-dilute colors like Cremello, Perlino, and Smoky Cream, which have blue eyes and pink skin.

The Gray gene is dominant and causes progressive depigmentation of the hair. Gray horses are born any color and gradually lighten over time, eventually becoming white or flea-bitten gray. A horse with even one copy of the Gray gene will turn gray regardless of its base color.

Tobiano is a white spotting pattern characterized by large, rounded white patches that typically cross the topline. Tobiano horses usually have white legs and a two-toned tail. The pattern is caused by a dominant gene, so a horse only needs one copy to display the pattern.

This calculator provides probability estimates based on Mendelian genetics. Actual outcomes may vary due to genetic factors not accounted for in this simplified model. For definitive answers about your horse's genetics, DNA testing is recommended. This tool is meant for educational purposes and general breeding planning.