The Thoroughbred is a horse breed best known as a race horse. While carefully bred racehorses had existed throughout Europe for centuries prior to this time, the breed as it is known today developed during the 17th century in England when English mares began to be bred to imported Arabian stallions. This addition of verifiable Arabian blood coincided with the creation of the General Stud Book of England and the practice of official registering of horses. Today all modern Thoroughbreds trace to these imported stallions. The typical Thoroughbred stands just over 16 hands (64 inches/1.63 m) high, and is bay, brown, chestnut, black, gray or roan in color. The face and lower legs may be marked with white, but white will generally not appear on the body (although certain color genes, possibly the rabicano or sabino genes, result in white hairs and white patches in the coat—the study of equine coat color genetics is complex).