In 41 breedings with the majority of the mares chestnut, all of the foals were black or near black. Of these breedings, three were known dominant recessive chestnuts. The chestnut genes of the palomino, red dun, and Haflinger all lost to the dominant black. In stepping out of his own breeding base of Arabian blood, a breed that has been bred along certain lines and strains for centuries, Serr Ebony Star has proven beyond any doubt the existence of dominant black occurring at the extension locus in all horses. All biochemical action occurring in living organisms take place in genes.
Genes appear on chromosomes which can be conceived as strings of genes.
These chromosomes come in pairs with an individual taking one of each pair from each parent. The homozygous black can only be proven by the breeding of blacks to chestnuts. If no chestnuts are born in at least 20 black to chestnut breedings, and that horse s sire and dam also had no chestnuts, the horse can be considered to be homozygous black. Since it is difficult to test a mare for twenty foals, stallions are usually the basis for study even though there may be plenty of homozygous mares. The homozygous black will often produce a bay but it will be a very dark bay, or nearly black, with the absence of the normal red tint associated with most bays.