07CoatColorGenetics 12/14/07 6:51 PM Page A 07CoatColorGenetics 12/14/07 6:51 PM Page B Contents The Genetic Equation of Paint Horses . .IFC Tobiano . .1 Overo . .1 Tovero . .3 Breeding the Tobiano Paint . .4 Genes . .4 Understanding Simple Dominance . .4 Using the Punnett Square . .4 Understanding genes, simple dominance and the Punnett Square . .4 Breeding the Tobiano Paint . .5 Determining Tobiano Homozygosity . .5 Breeding the Overo Paint . .6 Breeding the Frame Overo . .6 Defining Minimal-White Frame Overo . .6 Breeding the Splashed White Overo . .6 Defining Minimal Splashed-White Overo . .6 Breeding the Sabino Overo . .7 Defining Minimal-White Sabino Overo . .7 Breeding the Tovero . .7 Coat Colors . .8 The Basic Rules of Coat Color Genetics . .9 Overo Lethal White Syndrome . .16 Lethal Whites—Fact Versus Fiction . .16 References . .17 Color Description Guide . .BC For more information on the American Paint Horse Association and what it can offer you, call (817) 834-2742, extension 788. Visit APHA’s official Web site at apha.com. The Genetic Equation of Paint Horses Paint Horses are unique from most other breeds because of their spotted coat patterns. Their base coats are the same colors as those of other breeds, but super- imposed over these colors are a variety of white spotting patterns. The three patterns recognized by APHA are tobiano, overo and tovero. The ability to recognize these patterns and under- stand the genetics behind them is essential for Paint Horse breeders. Being knowledgeable about coat pat- terns helps breeders and owners accurately describe their horses. Understanding the genetics that produce these patterns helps breeders increase the proportion of spotted horses in their foal crops. Following are descriptions of the major Paint Horse spotting patterns. 07CoatColorGenetics 12/14/07 6:51 PM Page 1 Tobiano The first major pattern is tobiano (pro- arrangement. A tobiano’s Tobiano nounced: tow be yah´ no). The name tobiano eyes are usually dark. is itself unusual and has an interesting These horses can vary history. In Argentina, it is the habit to name from quite dark, with only small unusual colors after horses or people who amounts of white, to quite white, with little connect the color to a specific event or indi- remaining color. The darker individuals some- vidual. In the case of the tobiano horse, that times have so little white spotting that they event was the rescue of Buenos Aires by may be confused with nonspotted horses. Brazilian General Tobias during a military Minimally spotted tobianos are interest- action that took place in the 1800s. Many of ing because they are essentially tobianos the troops with Tobias were mounted on that did not get spots. These horses will tobiano spotted horses from Brazil. produce just like a spotted horse, however, This color pattern had occurred only rarely and that is the reason the pattern may in Argentina before this event (and was “mysteriously” appear in a breeding pro- lumped in with all the other spotting patterns gram for solid horses. as overo), but became firmly associated with A clue to identifying these “nonspotted Typical Tobiano Patterns Tobias and his troops afterwards, ending up tobianos” is that they tend to have a large taking his distinctive name. amount of white on the lower legs but little The tobiano pattern occurs in many white on the head. This combination is oth- breeds worldwide. It is common in pony erwise rare because it is usually the case breeds, some draft breeds and even that non-spotted horses with a great deal occurs in some of the warmblood breeds. of white on the head have a large amount In some breeds, tobiano spotting disquali- of white on the feet, and vice versa. fies a horse for inclusion in the registry— In the middle portion of the range of this in spite of the fact that the trait may tobiano spotting there is no problem telling have been present in some of the founda- tobianos from other Paint patterns. They are tion horses from which the breed sprang. quite distinctive. At the whitest extreme, many tobianos are all white except for a col- The characteristics of tobiano ored head. This pattern is sometimes called A tobiano’s feet and varying portions of “Moroccan,” although the connection to the its legs are usually white, the head usually country of Morocco or its horses is tenuous has no more white than normally found on at best. a non-spotted horse, and the spots usual- Other details of the tobiano pattern include the border, almost like a halo or a shadow. ly cross the topline somewhere between the fact that on many of these horses, the Another peculiarity of some tobianos is the the ears and tail. border between the white and colored areas presence of “ink spots” in the white patch- Tobiano spots are typically crisply delineat- consists of pigmented skin overlaid by white es. These spots are small and generally ed from the colored areas and have a vertical hairs. The result is usually a bluish cast to round in shape. Overo Typical Overo Patterns The second generally accepted type of different spotting patterns under one name, spotting is overo (pronounced: oh vair´ oh). and the result can be confusion in breeding Knowing the history behind the term overo programs. may be helpful in understanding the some- The term overo covers three genetically what confusing situation of having multiple distinct patterns: frame overo, sabino and patterns with one name. splashed white. Overo is a Spanish word, originally mean- ing “like an egg.” In this case, it refers to Frame Overo speckling or spotting. Long ago, in South The name “frame” refers to the usual America, the term overo was used for all the appearance, which is of white patches cen- various spotting patterns in horses: tobiano, tered in the body and neck, and framed by overo (all three types) and also the blanket colored areas around them. and leopard patterns typical of Appaloosas. The usual frame pattern has a horizontal In Argentina, the word overo is still used to arrangement and does not cross the topline, describe all the different spotting patterns as does tobiano. The overo’s head is usually other than tobiano. quite extensively marked with white and the In the United States, overo is usually used eyes are commonly blue. to mean “Paint, but not tobiano.” This has The feet and legs of frame overos are usu- resulted in the lumping together of three ally dark, although white feet and minor APHA Coat Color Genetics Guide • 1 07CoatColorGenetics 12/14/07 6:51 PM Page 2 Frame Overo with the gene can be Most have white extending from the belly mated to horses with- and have roan and flecked areas in addition out it, resulting in to white areas. However, a few will be near- foals that are about ly entirely roan without patches of white. half carriers and half- These could be confused with true roan non-carrier foals, but avoiding completely horses, although the facial and leg white the production of lethal whites. usually gives these away, and they do not have dark heads typical of true roans. Sabino Overo Another extreme is the sabino that is In literal Spanish, sabino (pronounced: patched, but not roaned. Sabino horses can sah bee´ no) means pale or speckled. In easily be confused with frame overos, espe- Europe, and increasingly in the United cially if they have one or two dark feet. Most States, sabino is used to describe a unique patched sabinos have smaller, more ragged and interesting pattern of white spotting in patches than is typical of frame overos. In horses. some cases, it is impossible to distinguish Sabino horses usually have four white feet between horses that are truly sabinos and and white legs. The white usually extends the frame overos that also happen to have white leg marks are as common on frame up the legs in ragged patches, and then white markings on their feet in addition to overos as they are on nonspotted horses. extends onto the horse’s body from the belly. the frame overo pattern. The white areas on frame overos are usual- The head is usually fairly white and the eyes The whitest of the sabinos are nearly or ly crisply and cleanly delineated from the are commonly blue. entirely white. Some retain color only on the colored areas, although some have a halo or Many sabino horses have partially blue, ears and others are white all over. One of shadow of pigmented skin under white hair partially brown eyes. Flecks, patches and the whiter ranges of expression includes directly at the boundary. roan areas are common on sabinos, in con- color on the ears, chest and tail base. These The frame overo pattern occurs in a lim- trast to the frame overos, which are usually are the Medicine Hat Paints that were prized ited range of horse breeds. It seems to more crisply marked. appear only in breeds that have Spanish Sabino occurs in a large num- Sabino ancestry, including the Paint Horse. ber of breeds worldwide, The genetics of frame overo has only including Paints, Thorough- recently been documented. Frame overo breds and Clydesdales. The pat- behaves as a dominant gene. It is common tern is commonly the cause of to mate frame overo horses to nonspotted spotted foals that appear in horses, and about half of the resulting foals breeds that frown on them, such are spotted. as the British pony breeds and On many occasions, though, there are the Quarter Horse. records of frame overos being produced by The sabino pattern is also a two nonspotted parents.