The genetics behind the black horse are relatively simple. The color black is primarily controlled by two genes: Extension and Agouti. The functional, dominant allele of the extension gene (labeled “E”) enables the horse to produce black pigment in the hair. Without this gene (homozygous recessive condition “ee”), the coat is devoid of black pigment and the horse is some shade of red. The functional, dominant allele (or alleles) of the agouti gene (labeled “A”) enable the horse to restrict black pigment to certain parts of the coat, notably the legs, mane and tail, allowing the underlying red to show through, resulting in bay coloring. Without this gene (homozygous recessive condition “aa”), any black pigment present is unrestricted, resulting in a uniformly black coat.