The recessive nature the chestnut or "red" coat in horses occurs because a single copy of the "E" allele is dominant over the "e" allele. Therefore, for example, bay and black horses may be heterozygous for "e" and if so, could produce a chestnut foal when bred to another horse with at least one copy of "e". However, all chestnut horses are homozygous for the "e" allele and thus breeding a chestnut to another chestnut will always produce a chestnut foal. Thus, unlike many coat colors, chestnut can be true-breeding; if any color other than chestnut occurs, then one of the parents was not chestnut.