Tobiano (TO) is a dominant gene. If tobiano is there it will express. Tobiano tends to create smooth round white patches on a horse. It also tends to travel up the back of the hind legs and over the rump to the other side. Sometimes the entire rump of the horse will be covered in white.Other times the white will stop just above the hocks, but will leave a stripe of white over the rump, or even in the tail. Tobiano in its minimal form can be as little as four white stockings. It rarely presents minimal enough to be mistaken for just white socks. Tobiano is also one of the few white patterns that never truly "hides." If a horse does not present as tobiano, even if its minimal, it is very likely NOT a tobiano. Tobiano wont be a completely solid horse, and it definitely will not hide for generations. Tobiano also does not cause blue eyes, nor any type of face white.
Here are a few examples of some tobianos.
This is Tru One Ina Million. He is by A Tru Rolex and was bred by Pine Springs Farm. He is homozygous for tobiano. He is Ee Aa TOTO. The movement of the white on his back left leg is very typical for a tobiano marked horse.
This is Sempatico. He is a Dutch Warmblood owned by Silver Wood Farm. He is EEaaTOTO. Notice the white going up the back of the leg and over the rump. Also notice the way the white travels from the front leg white up and over the neck.
This is Hall of Fame, another Dutch Warmblood owned by Silver Wood Farm. He is EeAaTOto. He has the classic tobiano pattern.
This is Extra Heir. He is heterozygous for tobiano. He is ee TOto. He is also marked like a classic tobiano, just a bit louder in expression. He stands at Riley Paint Horses.
If you have any questions regarding this post, or tobiano in general, post a comment and I will do my best to answer it.