this mutation have in moving from an ambling gait to a gallop, leading them to be easy prey for predators. Humans, however, have selectively bred for ambling horses, leading to a much more frequent occurrence of DMRT3 mutations among the human-bred horse population. Of note is that the trotting bloodlines of the Standardbred, though distinct from the pacing bloodlines, also are homozygous for the DMRT3 mutation, suggesting that it not only affects lateral gaits, but inhibits the transition to a gallop. In the studies of Icelandic horses, those animals homozygous for the DMRT3 mutation scored poorly for their ability to both trot and gallop. Researchers concluded that breeders selected away from the mutation in horses bred for sports such as dressage, show jumping, and racing at a gallop. Lateral ambling gaits Lateral gaits fall in the sequence right hind, right front, left hind, left front. They can be distinguished by whether the footfall rhythm is "even" or isochronous, four equal beats in a 1-2-3-4 rhythm; or non-isochronous, a slightly uneven 1–2, 3-4 rhythm created because the horse picks up and sets down its feet on each individual side slightly faster, creating a slight pause when switching to the opposite lateral pair of footfalls. Running walk The running walk is most often performed by Tennessee Walking Horses. It is a four-beat gait with the same footfall pattern as a regular, or flat, walk, but significantly faster. While a horse performing a flat walk moves at , the running walk allows the same horse to travel at . In the running walk, the horse's rear feet overstep the prints of its front feet by , with a longer overstep being more prized in the Tennessee Walking Horse breed. While performing the running walk, the horse nods its head in rhythm with its gait. Some Tennessee Walking Horses perform other variations of lateral ambling gaits, including the rack, stepping pace, fox trot and single-foot, which are allowable for pleasure riding but penalized in the show ring. "Slow gaits" The slow gait is a general term for several slower forms of the classic amble that follow the same general footfall pattern as the walk, in that lateral pairs of legs move forward in sequence, but the rhythm and collection of the movements are different. The common thread is that all are smooth gaits, comfortable to the rider. Terms for various slow gaits include the