sometimes is penalized for a diagonal gait, which in that breed is called trocha. Heritability and breeding In most "gaited" breeds, an ambling gait is a hereditary trait. However, some representatives of these breeds may not always gait, and some horses of other breeds not considered "gaited" may have ambling-gaited ability, particularly with training. A 2012 DNA study of movement in Icelandic horses, harness racing horse breeds, and mice determined that a mutation on the gene DMRT3, which controls the spinal neurological circuits related to limb movement and motion, causes a premature stop codon in horses with lateral ambling gaits. This mutation may be a dominant gene, in that even one copy of the mutated allele will produce gaitedness. Horses who are homozygous for the gene may have a stronger gaited ability than those who are heterozygous. Horses can now be tested for the presence or absence of this allele. In 2012, the mutated gene was found in the Icelandic horse, the Tennessee Walking Horse, the Peruvian Paso, and the Kentucky Mountain Saddle Horse. In 2014, a new study of the DMRT3 gene, now dubbed the "gait keeper" gene, examined over 4000 horses worldwide and DNA study found that gaitedness originated in a single ancient domestic ancestor as a spontaneous genetic mutation. In 2016, a study of DMRT3 SNP in paleographic DNA located the ambling horse mutation to medieval England with subsequent spread by Vikings first to Iceland in the 10th century. Breeds known for galloping ability, including the Thoroughbred and even the wild Przewalski’s horse, do not possess the mutated form of the gene. A number of horse breeds have observed natural gaited tendencies, including the American Saddlebred, Boerperd, Icelandic horse, Missouri Fox Trotter, Paso Fino, Peruvian Paso, Racking horse, Rocky Mountain Horse, Spotted Saddle horse, and Tennessee Walking Horse. The two-beat lateral pace is also sometimes classified with the ambling gaits as an "alternate" gait, and may be linked to the same genetic mechanism as the lateral ambling gaits. The pacing horses studied were all homozygous for the DMTR3 mutation. But not all horses with the homozygous mutation could pace, suggesting other factors had to come into play for that gait to occur. Although ambling gaits are seen in some Mustangs, and other Colonial Spanish Horses, DMRT3 mutations are rarely seen in feral or wild horses. Researchers theorize that this is due to the difficulty that horses with