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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 understand the genetics behind them is essential for Paint Horse breeders. Being knowledgeable about coat patterns 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

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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. This is typical of a great imitator, and some of these recessive gene, and it is not logical to have horses are nearly perfect mimics both a recessive and a dominant control of tobiano or frame overo. When over the same pattern. the sabino pattern is minimally Some of these horses are genetically frame expressed, the horse usual- overo, but have failed to get a body spot. They ly has four white socks are essentially very dark frame overos—so and a blaze. Usually dark that the spots are all gone from the body. there is some betrayal Splashed White They still have the gene, however, and can still of the fact that these produce frame overo-spotted offspring. are not the usual At the whiter extreme, frame overo is the white marks on horses, pattern most closely associated with Overo due to some ragged edge or long, Lethal White Syndrome (see page 16). narrow extension up the leg. Recent characterization of the gene Some sabinos also have odd white patch- responsible for lethal white foal syndrome es on the knee or hock, removed from the has confirmed that foals with two doses of main portion of the lower white mark. A the lethal white gene are white and die soon few sabinos do have a dark foot or two, after birth from gut innervation abnormali- although most have four white feet. ties. Horses with only one dose survive. Minimally marked sabinos are easily con- This documentation is important for fused with truly nonspotted horses. Paint Horse breeders. With DNA tests now In the middle range of expression, sabino available to identify the lethal white gene, it horses are fairly distinctive and are usually is possible to test breeding horses. Those difficult to confuse with other patterns.

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by the Native American tribes of Tovero the Great Plains. Most sabinos that are largely white are very speckled While each of the Paint Tovero and roaned, and some can be con- patterns—tobiano, frame overo, sabino and fused with Appaloosas. splashed white—can Some sabinos are quite white mark a horse on its and survive, which points to this own, many horses sport being entirely different from the combinations of these. When these overo that results in lethal white patterns combine, the result is a horse foals when homozygous. Sabino, with a pattern that can sometimes be by itself, is not associated with difficult to classify. lethal white foals. When a mating between a tobiano and an overo produces an offspring that exhibits Splashed White Overo characteristics of both patterns, APHA recog- Splashed white is the least com- nizes the resulting pattern as tovero (pro- mon of the spotting patterns, nounced: tow vair´ oh). (It should also be although it is increasing in frequen- noted that, while considerably rarer, a cross cy as breeders use more splashed between a tobiano and a solid can also pro- white horses in their breeding produce a tovero.) grams. In this instance, the combined patterns pick The pattern usually makes the up the white from each of their individual com- 4. Chest spot(s) varying in size. These may horse look as though it has been ponents. They are then genetically mixed to also extend up the neck. dipped in white paint. The legs are create a combination pattern on the horse’s 5. Flank spot(s) varying in size. These are usually white, as are the bottom coat. For instance, a horse with a frame overo often accompanied by smaller spots that portions of the body. The head is sire might inherit a white framed area on each extend forward across the barrel and up also usually white and the eyes are of its sides. If the horse had a tobiano dam, it over the loin. frequently blue. might inherit a white, blanket-like pattern that 6. Spots, varying in size, at the base of the tail. The edges of the white are typi- covers its entire back. The result might look Identifying the tovero pattern is not an easy cally crisp and clean, with no roan- something like the tovero shown on this page, task. During the Association’s early years, ing. Some splashed whites have which is mostly white. some toveros were mistakenly classified as dark toplines, but on some the Many of the combinations are called tovero tobianos or overos. In defense of the people white crosses the topline. because most are tobiano plus one of the who misclassified those animals, two points Recent genetic evidence suggests other patterns. must be made. First of all, during the registry’s that the splashed white pattern is Although the word tovero has been a part infancy, the pattern was much rarer than it is caused by a dominant gene, of APHA’s vocabulary from the onset of the now. There simply weren’t enough toveros because splashed white foals have registry, it remains to this day somewhat of an being registered to establish a workable pro- resulted from splashed white to ambiguous term. file of what their physical characteristics were. non-splashed white matings. Just as there are extremes within the Second, it had not yet been firmly estab- Some people have observed that tobiano and overo coat patterns—from most- lished how these horses would breed—what many splashed white horses are ly dark to mostly white—so are there extremes patterns they would produce that would prove deaf. This is not much of a problem within the tovero pattern. or disprove their classification. if the trainer realizes the limitations At one end of the spectrum—the mostly dark More than 40 years of Association growth of the horse in question and modi- one—are those toveros that closely resemble has alleviated both of these conditions, and fies the training program to meet tobianos except for their face markings, which the APHA Registration Department now has the horse’s special needs. Many of show an overo influence. At the opposite end— the situation well in hand. these horses go on to lead normal the mostly white one—are those toveros whose and productive lives. only dark pigmentation might appear around Typical Tovero Patterns Because no homozygous the ears, eyes or chestnuts. splashed white horses have ever In between those two extremes is the horse been documented, researchers sus- that can be termed the “typical” tovero, dis- pect that this is another gene that tinguished by the four basic coat characteris- cannot exist in homozygous form. tics shown below. Typical toveros have: If this is true, the loss of hearing 1. Dark pigmentation around the ears, which probably occurs early in gestation may expand to cover the forehead and/or rather than at term. Because of this, eyes. the best strategy for producing 2. One or both eyes blue. splashed white horses is to mate 3. Dark pigmentation around the mouth, them to horses without the which may extend up the sides of the face splashed white pattern. and form spots.

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Understanding genes, simple dominance and the Punnett Square Before you begin breeding for color, there and predict the probability of coat colors in nation is under the control of the recessive are a few basic genetic concepts you should their offspring. To help keep track of the gene, and in many cases this means there understand. Though genetics can seem genes whose function is thought to have is no expression. daunting at first, by understanding genes been identified, geneticists assign a letter For example, the recessive form of the and simple dominance, and knowing how to of the alphabet to the pair. gene for roan (Rn+), palomino (C), gray (g), use the Punnett Square, any horse owner tobiano (to) and dun (Dnnd) allow the body can plan their color breeding program with Understanding Simple Dominance coat to be expressed by the dominant gene. confidence. Gene interactions can be complex and Foals with a homozygous recessive par- confusing. Fortunately, some genes adhere ent will receive one copy of this parent’s Genes to a relationship based upon simple domi- recessive gene. Genes are the basic units of inheritance. nance. Within this framework, there are two Heterozygous—One member of the pair Genes are linked to form a chromosome basic expressions of the same gene—one is dominant, while the other is recessive, for similar to the way pearls are threaded dominant, one recessive. The recessive example, Aa. The dominant form is in con- together to make a strand. Each particular form of the gene is submissive to the dom- trol of the expression. Offspring have a 50- species has a specific number of chromo- inant form. The recessive gene is expressed 50 chance of inheriting either the dominant somes (64 for the horse), and each chro- only when both copies of the gene are in the or the recessive gene. mosome has a duplicate mate. recessive form. Each gene on the chromosome has a Capital letters usually indicate dominant Using the Punnett Square mate, or allele, in exactly the same place, or genes. Lowercase letters indicate recessive A Punnett Square is a simple way to pre- loci, on each of the chromosome’s matched genes. This system is complicated by the dict the possible genetic combinations from pair. Basically, each pair of genes codes for use of superscripts. For example, the dom- the mating of two individuals. To use this tool, a specific job. A pair of genes can control inant form of the gene creating palomino is first draw a square. Across the top, list the something as obvious as whether or not a CCcr. The recessive is referred to as C. gene combination of the stallion. Down the cow will have horns, or it may be as subtle Regardless of the letters used, each left side, list the gene combination of the as coding for a specific portion of a bimole- individual obtains one copy of the gene mare. Then, bring one value from each parent cular molecule, or controlling the function of from each parent. In the system of simple into the corresponding box within the square. other genes. dominance, this pairing occurs in one of During the cell division in which one cell three ways: Stallion (aa) Mated to Mare (Aa) divides into either two egg or two sperm Homozygous dominant—In this instance, Stallion cells, only one member of each chromo- both alleles are in the dominant form, as aa Mare some pair goes into each new cell. This indicated by a capital letter, for example, AAaAa aaaaa provides every sperm and egg with only AA. The color determination is under the one copy of each gene. Upon fertilization, control of the dominant gene, and all off- Each box represents a 25 percent every chromosome, and therefore every spring created from this individual can only chance of a specific gene combination. In gene, is reunited with its corresponding receive a copy of the dominant gene. the example above, foals from this cross mate to create a unique individual. Homozygous recessive—Here, both have a 50 percent chance of getting the Aa In coat color genetics, one of the goals is copies of the allele are in the recessive combination and a 50 percent chance of to identify the possible genes in the parents form, for example, aa. The color determi- getting the aa combination.

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Breeding the Tobiano Paint The tobiano pattern is under the control Tobiano of the dominant gene TO. The most common genotype for the tobiano is the heterozygous TOto. Fifty percent of the foals produced from a heterozygous tobiano should have the tobiano pattern. Fortunately, the homozygous tobiano TOTO exists. Having two copies of the homozygous tobiano is tobiano gene does not increase the amount more likely to be pro- of white on the horse, but individuals carry- duced if both tobiano par- ing this rare genotype can often be identi- ents come from tobiano fied by small dark hairs scattered in clusters parents. in the white areas of the coat. Not all Currently, there is not a homozygous tobianos have these “ink spots” laboratory test to identify the or “paw prints,” nor do these markings tobiano gene. Homozygous occur only in homozygous horses. However, tobianos are identified on the there is a strong association between this basis of other genetic evidence. pattern and the TOTO individual. To qualify as a homozygous Homozygous tobianos are beneficial to tobiano, a horse must be the breeding programs due to their ability to result of a breeding of two produce tobiano offspring. Statistically, tobiano parents. The horse every foal produced from the mating should should have a characteristic tobiano pattern, Homozygous Stallion (TOTO) Mated receive one copy of the dominant tobiano including ink spots, and a pedigree and to Heterozygous Mare (TOto) gene TO, thus creating a tobiano. breeding record that indicates homozygosi- Stallion Occasionally, a homozygous tobiano ty for the tobiano pattern. TO TO Mare mating produces a solid-looking horse. According to the Punnett Square, a TO TOTO TOTO homozygous homozygous This horse carries the tobiano gene but has homozgyous tobiano stallion mated to a TOto TOto only limited white markings. These horses heterozygous tobiano mare should produce to heterozygous heterozygous are often referred to as minimal-white 50 percent homozygous foals and 50 per- tobianos. cent heterozygous foals. No offspring passed on as a unit to the next generation, For these horses, the tendency of the should be solid. making their presence an important clue to tobiano to have a dark head and white legs determining a tobiano’s homozygosity. holds true. The head may be completely dark Determining Tobiano Homozygosity This fact creates the opportunity to trace or have very little white on it. However, the Breeding a homozygous tobiano should movement of the tobiano gene. legs will show the specific characteristics. produce all tobiano foals, with the excep- The ALB blood protein comes in two According to the late Dr. Ann Bowling in tion of a rare minimal-white. A horse that forms—A or B—while F and S are the sym- her book Horse Genetics, minimal-white produces five tobianos out of five solid bols given to the two forms of the GC gene. tobianos have dark spots or streaks in the mates is thought to have a 97 percent A major clue to determining tobiano white markings extending up from the coro- chance of being homozygous. Seven homozygosity is that 90 percent of the net. Also, the white extending over the tobianos from seven solid partners increas- time, the tobiano gene is associated with hocks ends as a horizontal line. es the odds to 99 percent. Ten tobiano off- the B form of the AL gene and S form of the As of this time, there has not been a case spring from 10 solid mates increases the GC gene. of a minimal-white tobiano that has failed odds to 99.9 percent. The blood test that is currently used in to have white leg markings. In addition, genetic marker analysis is the search for the homozygous tobiano Even though these horses are registered used to try to identify homozygous tobianos. determines which form of the AL and GC by APHA as solid Paints, they are, in fact, This analysis is similar to playing the game genes a particular horse has. tobianos and do pass on the dominant Clue. Certain facts are given, and then by the And don’t forget that the expression of the tobiano gene 50 percent of the time. process of elimination one tries to determine E provides a color trace for the tobiano Homozygous tobianos result from the which parent or parents supplied the gene, as well. This means that the tobiano mating of two tobiano parents. According tobiano gene. Remember, the horse must gene lies close to the gene that determines to the predictions of the Punnett Square, have been produced from the mating of two whether the base color of the horse is red or one out of every four foals produced by two tobianos. Tovero parents do qualify. black—e or E, respectively. The goal is to heterozygous tobiano parents should be a The tobiano gene is linked to a gene unit determine which form of the E gene is homozygous tobiano. comprised of the E gene (see page 12), the linked to the TO. Some Paint Horse breeders disagree with Rn gene (see page 17), and two other genes, (The roan gene, which is in the E Rn ALB the Punnett Square projections, maintain- ALB and GC, that code for blood proteins. GC unit, appears to commonly exist in the ing that the TOTO gene combination is These four genes lie so close together on the recessive form Rn+. It is extremely rare to harder to obtain. They also believe that a same chromosome that they are usually find a roan tobiano.)

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Breeding the Overo Paint Breeding the Frame Overo Little is known about the genetics that create Frame overos range from being nearly totally white to the minimal-white indi- overo patterns. It is commonly accepted that vidual. The minimal-white frame overo characteristically has a lot of white on its overo patterns are under the influence of one or face and a solid body with minimal white leg markings. more dominant genes. It appears that each of the Regardless of the expression of the frame overo pattern, these horses pro- patterns may be the result of a dominant gene, duce overo foals 50 percent of the time. It has been hypothesized that the frame but it is also possible that there is only one gene overo is under the control of a single gene, which is designated Fr. and that gene modifiers change the pattern. Frame overos are known to produce lethal white foals. It is not known at this There is also some evidence that the genes time whether this condition is created by a homozygous frame overo—FrFr— but the condition is highly correlated with large amounts of white on the foal. that produce leg and facial markings may influence the amount of white on an overo. This Defining Minimal-White Frame Overo appears to be true for the sabino and splashed • A great deal of white on the face. white patterns. • Solid bodies. The frame overo, like the tobiano, is thought • Normal solid horse, to be less sensitive to these genes. minimal leg markings. Time and research will eventually answer Frame Overo These horses may be these questions. For now, here is what the three registered as overo patterns seem to have in common. Solid Paint-Bred, but All the overo patterns have a large range of in reality they are expression. At one end, they appear mostly overos and will white. At the other end, a minimal-white overo produce overos may be hard to distinguish from a solid horse. 50 percent These minimal-white overos may be the reason of the time. that so many breeders think that overo appears at random from solid horses. It may also be the rea- soning behind the belief that it is easier to get an overo by breeding an overo to a solid that has an overo parent. These overo breeding stocks may be minimal-white overos. The development of a test to determine the presence of the overo gene(s) will go a long way toward sorting out this confusion. The possibility of there being a homozygous overo does not look good. It is thought that the homozygous overo is plagued by the lethal white syndrome. Lethal white foals die shortly Breeding the Splashed White Overo after birth due to lack of proper development According to Dr. Bowling’s work, the splashed white pattern is under the control of a dominant gene identified by the letters Spl. At this point, there has not of their digestive systems. been a documented mating of two splashed white overos creating a homozy- There have been cases of lethal white syn- gous individual. drome occurring from the mating of an overo to a solid. Because of this, the question Defining Minimal becomes: Were these solid horses minimal- Splashed-White white overos carrying an overo gene and there- Overo Splashed White Overo fore producing a homozygous overo foal, or is • A great deal of there some other gene action associated with white on the overo that occasionally produces foals with the face. the lethal white syndrome? • Solid bodies, To confuse the matter further, each overo perhaps with a small white spot pattern has the ability to produce nearly white on the belly. normal foals. This is not to say that these foals • White leg markings. may not be plagued by some of the other prob- These horses may be registered as lems associated with mostly white horses. Solid Paint-Bred, but in reality they are There is some evidence that deafness may overos and will produce overos occur more often in nearly white horses. And 50 percent of the time. with age, the pink skin around the eyes of a white horse quite often develops cancer. In spite of the similar action of the hypothesized overo genes, each type of overo has a characteristic pattern.

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Breeding the Sabino Overo Tovero The color pattern referred to as sabino foals come out with fairly encompasses a wide range of patterns. It minimal expression. In the is possible that more than one pattern has Clydesdale, this means been included in this category, but at the few body spots and rel- moment we are going to assume that this atively few roans, which is the varied expression of a single gene. pleases most breeders and buyers of this This gene has been designated as the breed. They still do get the occasional dominant Sb gene. Medicine Hat, though. Lethal whites have occurred from the Some horses that lack body spots, but mating of two sabinos, but viable white that have the high white socks that creep foals have also been documented. As with up toward the body, are indeed sabinos all the overo genes, the wide variation in and can be useful in Paint breeding pro- pattern leads to a lack of predictability. grams. The sabino pattern is a great pre- The sabino pattern is confusing geneti- tender, but is also responsible for some cally. In many, or most, families, it appears very attractively marked horses. to be transmitted as a polygenic trait The sabino pattern is probably the most Breeding the Tovero rather than as a single gene. Many horses common “cropout” from the Quarter appear to transmit it roughly in the per- Horse and Thoroughbred breeds. In many The most interesting thing about Paint centage that they are themselves white. cases, an investigation of the cropout’s genes is that all four seem to be capable of That is, a sabino Medicine Hat is likely to parents reveals horses with extensive combining with each other. The pattern cre- produce a higher percentage of spotted white markings. In reality, these parents ated through the action of the tobiano gene foals (or at least foals registerable as spot- are probably minimally marked sabinos, and any overo gene is referred to as tovero. ted) than is a minimally marked sabino. which occasionally produce foals with This name does not indicate which overo Breeding for the sabino pattern has a more sabino expression than themselves. gene is present—just that the overo and few interesting quirks. In many breeds it is A few cropouts, including nearly white tobiano genes are being expressed in the desirable to have flashy white marks, but ones, have very dark parents, or even par- same individual. not body spots. This includes the ents with no white marks. These parents It is possible that many overo horses have Clydesdale, Shire, Welsh Pony, Arabian are clearly not sabinos, and demonstrate more than one overo gene creating their and even the Quarter Horse (for some that there may be mechanisms that can color pattern. The Medicine Hat Paint has breeders). mask the expression of the sabino pattern. been documented as being produced by Clydesdale breeders especially like the If the sabino pattern is merely an exten- crossing frame overos on tobianos, sabinos white marks, but most prefer a bay body sion of “normal white marks,” then this on frame overos and sabinos on tobianos. color. The general rule that many means that an occasional solid-colored From a color breeder’s point of view, Clydesdale breeders use is to mate horses horse (with no white marks) may be able intriguing statistics are derived from horses with four white feet (and usually roany to mask both white marks and the sabino carrying more than one copy of a Paint gene. bodies, resulting from the sabino pattern) pattern. The practical consequence of this Ignoring the homozygous tobiano that pro- to horses with one dark foot. This tends is that such horses make poor choices for duces tobiano foals 99.9 percent of the time, to result in the mating of horses with too an outcross breeding program because a horse carrying two separate Paint genes much sabino expression to those with too they can decrease the percentage of spot- should produce a spotted offspring 75 per- little expression. On average, the resulting ted foals. cent of the time from solid mates. A horse having three independent Paint genes is thought to produce a Paint foal 87.5 percent of the time. For the horse carrying four Paint Sabino Overo genes, the percentage of spotted foals from solid partners hits an amazing 94 percent. So, if the theory is correct and each overo pattern is under the control of a separate gene, there is more than one way to increase the odds of producing a spotted foal. Defining Minimal-White A Paint with one color pattern gene bred Sabino Overo to a Paint with two Paint color genes pro- • A great deal of white on the face. duces a spotted foal 87.5 percent of the • Possible small roaned areas on the body, time. If both Paint parents have two Paint often expressed as a narrow white strip up color-pattern genes, the odds of producing a leg or down the throat. a spotted foal are greater than 99 percent. • Normal solid horse, minimal leg markings. The problem is that multiple copies These horses may be registered as Solid of Paint genes produce more white on horses, Paint-Bred, but in reality they are overos and and some pairings may create lethal white will produce overos 50 percent of the time. foals.

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Coat Colors A good horse is a good horse, regardless Perhaps it is because of this variety of whenever the gray gene is present, the horse of its color. Yet, color can be a major asset preferences that coat color genetics is one of is gray regardless of basic coat color. Horses when a horse is for sale, and it can make a the few areas of equine genetics where sci- of any color (with the exception of true difference in the amount of attention a horse entists have been able to develop sophisti- white) can gray. gets in the show ring. cated theories about how specific genes The American Quarter Horse Association, In addition to sporting various patterns determine the color of a horse’s hair. trying to keep up with the current coat color of white patches—expressed as tobiano, However, it is important to realize that theory, has changed the description of a frame overo, sabino, splashed white or much of the theory of coat color genetics is “buckskin.” In the past, a buckskin was any tovero—every Paint Horse also has a back- just that—theory. At this point in time, only canvas-colored horse with black points. It ground color. the presence of four color genes can be con- could have zebra markings and a line-back Coat patterns have many background col- firmed in the laboratory: the tobiano gene, and still be a buckskin. Today, all line- ors, and controlling them genetically can be the recessive form of a gene that creates a backed horses with zebra markings are complicated. Anyone wishing to breed for red horse, the cream gene and the agouti referred to as duns by AQHA, unless they specific background colors has an interest- (bay/black). are sorrel or chestnut duns. These are called ing challenge before them. The breeder The action of the rest of the color genes is red duns. Black duns are called grullos. must combine specific colors with specific purely hypothetical. Because of this, theo- APHA’s color criteria is the most descrip- Paint spotting patterns, which requires care- ries may change as more tests become avail- tive of the three associations when it comes ful planning and a knowledge of genetics. able to identify specific genes. to roan, giving roan three basic colors: black Some Paint breeders prefer darker back- Identifying coat colors can also be confus- (blue), bay and red. Starting in 2000, it ground colors, such as bay, chestnut and ing. There is a tremendous range of shades became possible to register bay roans, while black, over the lighter colors such as dun, within a color, and different types of color the term red roan designates sorrel/chestnut palomino, grullo or buckskin. The reason without recognized names. There are also roans. for this preference is because the contrast coat colors that appear to be identical but are If all of this sounds confusing, take heart. between the white Paint patterns and the under the influence of different genes. It is possible to stack the deck in your favor darker base colors shows up better than it Breed associations have also contributed when trying to produce a specific-colored does with the lighter colors. to some of the confusion. Thoroughbreds offspring—if you understand the underly- This rule, though, is not absolute, and the registered by the Jockey Club are called ing genes that create the colors. light-colored duns, grullos, buckskins and roans if they have a red body with white palominos are popular among many breed- hairs. According to their definitions, grays ers. Taste in color is an individual preference. are dark horses that are graying. Technically,

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The Basic Rules of Bay Horses Bay is the second most common horse color. Controlled by the A gene, a Coat Color Genetics bay horse has a reddish brown body with black points. The A gene creates While it is true that the control of color is complicat- these black points by limiting the placement of black on the horse’s coat to ed, it is also true that the lighter colors are all dominant the mane, tail, legs and ears. to the darker ones. This general rule is oversimplified, The two genetic loci (locations) that control the color of the bay, black but it works in most cases. and sorrel horse are the Agouti (A) and Extension (E). The way these loci Therefore, the light colors do not pop out—except interact creates these three rarely—as surprises. That is, you have to breed to a basic body colors. Heterozygous Bay (AaEE) light color to get a foal of a light color. This fact has Agouti controls the distri- Mated to Chestnut (Aaee) some consequences for Paint breeders. bution of the red and black Bay If the breeder prefers the darker base colors, then it areas on horses that can form AE aE Chestnut is important to always select the darker colors for their black pigment, i.e., blacks, AAeE AaeE Ae bay bay breeding programs. This is especially true if outcross- bays, buckskins, etc. es are sought, because the lighter colors are fairly com- aAeE aaeE The dominant A gene ae bay black mon in the Quarter Horse. They are present, but rare, restricts black to the points, in the Thoroughbred. creating a bay. The recessive Agouti gene (a) does not restrict the black, result- On the other hand, if the light base colors are desired, ing in an all-black horse. Therefore, foals with the genotype AA or Aa will be then it is important for the breeder to always include at bay and those with the aa genotype will be black, providing they have the least one light-colored parent in matings in order to dominant Extension gene. boost the chances of producing a light-colored foal. The Extension locus interacts with the Agouti to restrict or allow the The downside of using two light-colored horses in a expression of black, but unlike the bay gene, it is the recessive form of the cross (specifically palominos and buckskins) is the Extension loci that does not allow the color. As a result, a foal inheriting two occasional production of cream-colored horses—the copies of the recessive black gene (ee) will be completely sorrel or chestnut, cremello and perlino. These horses are nearly white, regardless of what type of Agouti alleles it carries. and it is difficult to see the contrast between any Paint In his book Equine Color Genetics, Dr. Philip Sponenberg describes the spotting and the pale background color. Agouti and Extension loci as switches. As a way to remember the effect each The line-backed dun colors only rarely can produce gene has on a horse’s color, one can imagine that the Extension locus deter- a cremello foal, making them safer to mate to other mines if the horse is “chestnut” or “not chestnut.” If the horse is “not chest- light colors because cream foals occur in such mat- nut,” then the Agouti locus acts as a switch to determine if the horse is “bay” ings infrequently. or “black.” The darker colors, usually considered to include bay, Understanding how the A and E genes work to create the bay color and affect chestnut and black, are easier for most breeding pro- the occurrence of sorrel and black will help you to better determine how other grams. These have a peculiar interaction in that chest- coat colors are created. However, there are still many subtle shades of the bay nut (and sorrel) are recessive to bay and black, but act coat that cannot fully be explained by the action of the A and E genes. to cover them up. This means that it is impossible to tell Bays range in color from dark mahogany bays to blood bays to golden just from looking whether a chestnut or sorrel horse has bays. These bay shades are thought to be under complex, multifactor genet- the genetic makeup to produce black or bay. Testing for ic control. Even environment and nurture can cause a variation in coat color, the Agouti gene is helpful. with well-fed horses having a deeper, richer coat than those lacking in nutri- Reviewing the rules tion. Again, Sponenberg says these variations can be viewed as switches that To review, the basic rules for producing colors are: trigger either a “dark,” “middle” or “light” shade. • It usually takes at least one light-colored parent to Regardless of the many color variations, bay foals are all born with black produce a light-colored foal. tips on their ears. In addition, most of have black manes and tails; • Chestnut and sorrel, when mated to one another, can however, their legs may be light at birth and later produce only more chestnuts and sorrels. shed to black. • Bay mated to bay, black or chestnut/sorrel can produce bay, chestnut, sorrel, and, rarely, black. • Black mated to black produces black (or, rarely, Bay chestnut or sorrel). • Black mated to bay will usually produce a bay, fairly commonly produces chestnut or sorrel, and only rarely produces black. • Black mated to chestnut will usually produce bay, but also chestnut or sorrel, and, rarely, black. Color prediction is never 100 percent accurate. The best way to maximize the chance of a specific dark color is to test for the Agouti gene or to mate two parents of that color. Any other approach drastically decreases the probability of achieving the desired color in the foal.

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Black and Brown Horses Chestnut The black coat color is controlled by the E gene. It is the expression of the dominant E gene. The homozygous black horse (EE) has a very rich, black coat that is sometimes called jet black or coal black. Black horses have an entirely black coat and their color does not fade out over the flanks in the summer. Though they are recognized by APHA as a separate color, brown horses are also genetically controlled by the E gene. Brown horses have black or nearly black coats with brown or reddish hairs on the muzzle or flanks. Black is a popular color with many breeders, but it is Sorrel fairly rare. The most reliable way to produce black horses is by mating two homozygous black horses. Breeding two heterozygous blacks is the second choice and breeding a black to any other color horse that carries a black gene is third. The reason for this is that the E gene is dominant over the e and the CCcr genes that are present in palominos. Fortunately, breeders can have their black or brown horse tested for the recessive e gene so that they can determine if it is homozygous (EE) or heterozygous (Ee). The problem with breeding black to sorrel is that many red horses carry the A gene, which turns the black coat to bay. According to statistics, a heterozygous black and a chestnut should produce a black foal 50 percent of the time. Chestnut and Sorrel Horses However, this is valid only if the chestnut horse (ee) does not The chestnut horse and the sorrel horse are homozygous reces- carry the A gene. If the chestnut parent is heterozygous for this sive ee individuals. Though there is no distinction between the two A gene, 50 percent of the blacks will become bays. If it is colors in the Jockey Club, most breed associations consider the homozygous for this gene, 100 percent of the foals will be bay. chestnut and sorrel Mating Heterozygous Black (Ee) Black foals are usually born with a blue-gray hue to their coat different. Mated to Sorrel (ee) and will typically shed to black as weanlings or yearlings. Both have a reddish body color with Black Ee Mating Two Heterozygous a reddish mane and Black Parents (Ee) Sorrel eE ee tail, which can vary e black sorrel Black from dark to light to eE ee Ee flaxen. The differ- e black sorrel Black EE Ee ence is in the E black black Brown depth of the body color. Chestnuts are a darker red that is eE ee e black sorrel sometimes close to black. Sorrels are a lighter or bright red. For the purpose of learning to utilize color genetics, this guide will use the terms interchangeably, because both colors are created by the homozygous recessive e. Chestnut and sorrel come in many shades—from very light sorrel, which can appear close to a palomino color, to black chestnut. The best way to distinguish a black chestnut from a black or brown horse is by the copper-colored highlights on its legs. Regardless of shade, two chestnut parents will always pro- Black duce a chestnut foal, making it the easiest color to breed for. Mating of two heterozygous blacks (Ee) will produce chestnuts 25 percent of the time. In addition, sorrel is a valuable color when trying to breed colors based upon the red color, like palomino, red roan and red dun. Sorrels that have two copies of the recessive Agouti locus (aa) are valuable to breeders raising black horses because they will not turn black to bay. For the same reason, it will never produce a bay roan when bred to a blue roan. A test is available to determine the genetic A code of sorrel individuals. Sorrel and chestnut foals are born with reddish coats that may lighten or darken when they shed.

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Champagne and Cremello Genes Cremello and Perlino Horses Scientists have identified three genes that create the A horse that receives two copies (CcrCcr) of the cremello gene coat colors palomino, buckskin and dun. Of these genes, has a cream-colored coat with pink skin and blue eyes. When the champagne and the dun (see page 13) gene, express two pairs of Ccr occur in a horse with a chestnut base color, the themselves according to the rules of similar dominance. resulting body coat color is called cremello. When two Ccr genes As a result, they dilute the horse’s base color only when occur in a horse with a bay base color, it creates a color known the dominant expression of the gene is present. Whether as perlino. the horse has two copies of the dominant gene or only As foals, a perlino and cremello look almost identical, both one, the coat color looks the same. with pink skin, blue eyes and a washed-out coat color. White markings on the face and legs are barely visible next to the slight- Palomino/Buckskin (CcrC) Mated to ly yellow coat. Sometimes, these foals are mistakenly referred to Palomino/Buckskin (CcrC) as albinos. Palomino/ Many breeders will not mate two palominos because of the Buckskin chance of raising a cremello. Using the Punnett Square, you can Ccr C determine that 25 percent of the foals from a palomino-to- Palomino/ cr cr cr cr Ccr C C C C palomino mating will receive two copies of the CC gene. Buckskin homozygous dilution Breeding palominos to buckskins, or buckskins to buckskins, dilution (cremello/perlino) results in a 25 percent chance of raising a perlino. The cremello cr gene creates both the buckskin and the palomino—the only dif- C CC CC dilution no dilution ference is the base color upon which it is acting. Both palominos and buckskins result from the heterozygous (CcrC) cremello gene The Champagne Gene combination. However, the buckskin’s base coat color is bay, and The champagne (Ch) gene is not as commonly recognized the palomino’s base coat color is sorrel or chestnut. as some other genes for coat colors. The dominant form of The benefit derived from cremello and perlino breeding stock the champagne gene (ChC) gives horses an iridescent glow is that Paint breeders can produce palominos and buckskins 100 to their coats. Their eyes are amber and their skin is pump- percent of the time. A cremello bred to a sorrel will always pro- kin-colored or a pinkish-gray. Researchers have identified duce a palomino and a perlino bred to a bay or sorrel will always the gene in the Tennessee Walking Horse, the Rocky produce either a palomino or buckskin. Mountain Horse, the Quarter Horse and the Paint Horse. In his book Equine Color Genetics, Sponenberg reports that the champagne gene dilutes a chestnut coat to golden with a flaxen mane and tail (golden champagne). Its action on black turns the coat to classic champagne, the bay coat becomes tan with a dilute mane and tail, known as amber champagne, while the Perlino action on brown becomes sable champagne. A champagne-dilute foal is often born dark-colored and will lighten to champagne when it sheds for the first time. For this reason, it is likely that many champagne horses have been registered as palomino, buckskin and sorrel. Owners of champagne horses who want their horse’s color recognized can contact the International Cham- pagne Horse Registry, which is the official registry for the color. To find out more, log on to their Web site at ichregistry.com. Cremello The Cremello Gene The cremello gene produces the palomino and buckskin color, but unlike the other dilution genes, it follows the rule of incomplete dominance. As a result, the gene can express itself in three ways, depending on the combination in which it occurs. One copy of the dominant (Ccr) gene turns the horse’s coat to either palomino or buckskin. Two copies of the Ccr gene dilute the coat to perlino or cremello. The cremello gene is not expressed when it occurs in the homozygous recessive (CC) form. The same rule applies to the champagne and dun genes.

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Palomino Horses The palomino horse is a chestnut horse (ee) with one Ccr gene. The Palomino Horse Breeders of America, a color breed registry for palominos, describes the color as that of a U.S. 14 karat gold coin, with variations from light Palomino (eeaaCcrC) Mated to to dark. However, the body coats can Heterzygous Bay (EeAaCC) vary from a smoky gray to creamy yel- Palomino low. Palominos may have manes the eaCcr eaC cr color of their bodies or they can be Bay EAC EeAaCC EeAaCC white, silver or mixed with sorrel. Their buckskin bay cr eaC eeaaCC eeaaCC skin is usually gray, black, brown or mot- palomino sorrel tled, without underlying pink skin or spots except on the face or legs. A palomino foal’s true color may not For breeders who cannot utilize be evident at birth. Some will have yel- cremellos or perlinos in their breeding lowish bodies and white manes and programs, crossing a sorrel with a tails, making them easy to identify. But palomino has the best odds of produc- some are born with a sorrel coloring. ing a palomino—a 50 percent chance. These foals tend to have an orange or A palomino mated with a black horse resulting foal can receive an eeCcrC pink tint to their coats, and their manes may produce a palomino or a black foal, combination, making it a palomino. and tails may be slightly red. As wean- depending on which black gene combi- A variety of coat colors can result lings or yearlings, these foals will shed nation it receives. The black gene (E) when breeding a palomino to a het- their sorrel coat for their true palomino masks the expression of the Ccr gene. erozygous bay. These foals have a 25 color. This is why a black horse crossed on a percent chance of becoming buckskin, Fortunately, a breeder in doubt has palomino is the third-best way to pro- palomino, bay or sorrel. one sign on which they can rely. The duce a black foal. Also, a heterozygous Of course, the Punnett Square only esti- color of the foal’s eyelashes provides a black (Ee) horse with a palomino parent mates gene action, because there are good clue to the foal’s eventual coat can produce a palomino if it passes on a other factors that change breeding per- color. Palominos born with sorrel coats recessive e and a Ccr. If that horse’s centages. Its predictions work over a large usually have light, golden eyelashes. mate also has the recessive e gene, the population, but any horse can deviate.

Buckskin Horses Buckskins are canvas-colored with black tips on their ears and black legs, like bays. Their body color ranges from purple to sand to cream. Buckskin is produced by the dominant cremello gene (Ccr) acting on a bay base color. Buckskin foals are fairly easy to identify at birth. Born with light bodies and black ear tips, their legs may be dark but usually appear light and then shed to dark. Markings can be tricky to detect on a buckskin Paint when the Paint gene colors the legs white. Hoof color can sometimes be helpful, as a buckskin Paint should have dark hooves. For breeders who cannot utilize cremellos or perlinos in their breeding programs, crossing a bay with a buckskin is the second-best way of producing the Palomino (eeaaCcrC) Mated to color, with a 50 percent chance. Homozygous Bay (EEAACC) A 50 percent chance can Palomino also be obtained by breeding eaCcr eaC a palomino to a bay that cr is homozygous for the black Bay EAC EeAaCC EeAaCC buckskin bay gene and the bay gene (EEAA). cr EAC EeAaCC EeAaCC This cross also produces 50 buckskin bay percent bays.

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Dun Horses The coat color categorized as dun has one often continues into the mane Heterozygous Dun (eeaaCCDn+Dnnd) Mated of the broadest ranges of colors and mark- and tail, where the gene action to Homozygous Bay (EEAACCDnndDnnd) ings. For APHA purposes, horses with a dun darkens the center of the hair Dun coat are categorized as either dun or red dun. and leaves the edges lighter. eaCDn+ eaCDnnd Dun is the result of the dominant dun Dark-colored horses such as Bay nd + nd nd EACDnnd EeAaCCDn Dn EeAaCCDn Dn gene (Dn+) working on a bay base coat. The black, bay and chestnut may have dun bay nd + nd nd effect is to lighten the body to a tan or gold- a back stripe without a lightened EACDnnd EeAaCCDn Dn EeAaCCDn Dn en yellow color. A red dun occurs when the body color. Similarly, foals are dun bay Dn+ gene expresses itself on a chestnut or sometimes born with a lineback sorrel coat. Red duns have a light red, that disappears when they shed. However, probably not related to the dun gene (Dn+). orangish or sometimes apricot coat color. scientists believe these back stripes are not Following the rules of similar dominance, All duns, regardless of body color, have one caused by the dun gene. These back stripes the recessive dun gene (Dnnd) does not affect thing in common—primitive markings. There are referred to as “counter-shading”. the outcome of a horse’s color. Scientists still are basically four types of primitive markings: Dark edging on the ear is another com- do not know if the dun gene acts alone, or if zebra stripes, dorsal stripe (lineback), withers mon dun characteristic, but because this there are other genes that work to create the stripe and cobwebbing. Zebra stripes are bars characteristic is common in other colors, it is many different dun characteristics. on the side of the hocks and above or below the knees. A dorsal stripe is a dark stripe down Primitive Markings the back. A withers stripe is a stripe across the withers, and cobwebbing is expressed by con- centric darker rings on the forehead. Not all duns express each of these traits, but some do. They can have any combination of these markings. Researchers believe the dun gene lightens the body, leaving the horse’s dark points unaf- Leg Barring: Shoulder/Traverse Stripes: Dorsal Stripe: fected and leaving the head darker than the Horizontal stripes of Neck and shoulder Darker band of color run- body. The mane and tail are also often darker. varying widths appearing shadowing appearing as ning along the backbone The lineback is the most common dun across the hocks, gaskins, dark areas through the from the withers to/into the feature. The darker color of the lineback forearms or knees. neck or withers. base of the tail.

Grullo Horses Grullo is one of the rarest expressions of cremello gene (CCcr) will result in a paler Scientists believe that when CCcr x Dn+ the dun gene because it results from the grullo. On a bay base coat, the primitive occurs, the gene that has the most extreme action of the dun gene on a black base marks may remain but the body becomes expression of the base coat color is the one coat. It was once believed that grullos more yellow, like a buckskin. On a sorrel that is dominantly expressed. For instance, resulted from crossing palominos with black coat, the primitive marks may be lost alto- a chestnut coat would be lightened to horses, but genetic research has since gether and the body becomes the color of palomino because palomino is a more proved that theory incorrect. a palomino. For this reason, the colors of extreme change than is red dun. The grullo coat varies from beige to bluish- some horses may gray to slate blue. They usually have dark or have been incorrect- black heads and black points, mane and tail. ly registered, which As the dun gene acts through similar could explain why dominance (see page 14), grullo is created breeders once by a single copy of the Dn+ gene. However, believed a palomino homozygous duns (Dn+Dn+) do exist and could produce a will pass on a dominant dun gene to each grullo. In actuality, the of their offspring, resulting in 100 percent palomino was a duns and grullos. palomino- Another interesting result colored dun without the dorsal stripe. of the dun gene occurs when a horse also carries Heterozygous Black (EeaaCCDnndDnnd) Mated the dominant form of the to Heterozygous Red Dun (eeaaCCDn+Dnnd) cremello (Ccr) gene, which Black creates cremellos, perlinos, EaCDnnd eaCDnnd palominos and buckskins. Red + nd + nd eaCDn+ eEaaCCDn Dn eeaaCCDn Dn A black horse that receives Dun grullo red dun nd nd nd nd the Dn+ gene and is eaCDnnd eEaaCCDn Dn eeaaCCDn Dn also heterozygous for the black sorrel

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The Difference Between Roan, Roan Gray and White Roans are often confused with gray horses dominant E (black) gene, is apt to produce Three of the most easily confused because both are characterized by having a high percentage of black and bay roans. If colors are roan, gray and white. white in their hair coats. However, the differ- a horse’s roan gene is linked to the recessive Though all result from white being ence between the action of the roan gene and e (sorrel) gene of a heterozygous (Ee) indi- added to the horse’s base coat, each the gray gene is evident once you understand vidual, the horse should produce only red has a unique way in which it occurs. the specific effect each has on a horse’s coat. roans when bred to sorrel mates. The roan gene (RnRn) covers specific The action of the RnRn gene places a certain Homozygous roans are extremely rare. parts of the body with a light coating of amount of white hairs in the body coat. Though it was once believed that the white hairs that are evenly mixed within Sometimes, the roan pattern is uneven and is RnRnRnRn combination was lethal, the exis- the base coat. The gray gene (G) begins displayed in a paler fashion on areas such as tence of a few homozygous roans disproves as a light sprinkle of white over the entire the hindquarters, the heart girth, the barrel and this theory. coat. Each year, more white hairs are the dock of the tail. Unlike the gray horse, a It is important to keep in mind that the added to the coat until it is completely roan’s head, mane, tail and lower legs usually genetic codes controlling the roan gene are gray or white. The white gene (W) com- remain solid or darker than the rest of its body. extremely complicated, so this is only a basic pletely covers the body with an even, A roan foal’s color may be evident at birth, or discussion of the coat color. Without a doubt, white coat before the foal is born. may reveal itself after it sheds its foal coat. A there is an exception to every rule and a hid- By becoming familiar with the spe- roan horse does not grow more white hair as it den factor that cannot be seen on the surface. cific characteristics unique to each ages. Instead, a roan coat may appear lighter color, a breeder can reliably identify in the spring and darker in the winter months. Blue Roan one from the other. Because these The roan gene is dominant. It is believed Blue roan is the common term for the three genes add white to the basic coat to be linked to other genes that determine the RnRn gene acting on black. White hairs are color of the horse, the horse’s other horse’s color, which complicates determining dispersed over the body, giving a blue gene combinations of E, A, Ccr, Dnnd, the inheritance of the gene because these appearance to the horse. The head, legs, Ch, etc., still determine the color that is linked genes are usually passed along as a mane and tail are very dark. being covered by the coating of white. unit. The roan gene is closely associated with the E gene, which determines a red or black Red Roan base color, and the TO (tobiano) gene. Thus, The base coat of a red roan is sorrel or Blue Roan (EeRn+RnRn) Mated to roans have a higher percentage of offspring chestnut. Red roans have a uniform mixture Sorrel (eeRn+Rn+) that are the same color as the roan parent. of white with red hair on a large portion of Blue Roan For example, red roans, which have a sor- the body, but are usually darker on the head + Rn E Rn eRn rel base coat, bred to sorrels, produce 50 and lower legs. The mane and tail may be + + + Rn Sorrel + eERn Rn eeRn Rn percent sorrels and 50 percent red roans. A red, flaxen or white. eRn black red roan + + + Rn blue roan, whose roan gene is linked to its Red roans with white legs and a blaze face eRn+ eERn Rn eeRn Rn black red roan are often referred to as strawberry roan, a term APHA does not officially recognize. Horses with strawberry roan markings Blue Roan have shown a tendency toward producing Bay Roan excessive white by Quarter Horse standards. It may be possible to influence the occurrence of excessive white by carefully screen- ing the mates for strawberry roans. Chestnut horses with stockings and blazes increase the chance that the white markings will spread. Solid-legged and solid-faced mates may help to keep the color to a minimum. Researchers have also discussed the possibility that some of the strawberry roan markings are an expression of the sabino overo pattern gene. Red Roan Bay Roan The bay roan, which has a bay base coat, is often called a red roan. APHA distinguish- es between roans with bay base coats and those with sorrel or chestnut. The category of bay roan was added to the registration form, separating the two basic coat colors. Only sorrels and chestnuts with the roan gene are now registered as red roans.

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Gray Horses With horse people and non-horse people Gray horses are alike, gray is one of the most popular coat born with a col- colors. Perhaps this is because it seems to ored coat such hide conformational faults and can make a as black, bay, plain head appear beautiful. sorrel, dun, The irony is that gray is often an undesir- etc. Their foal able gene for breeders of white-patterned coat typically reflects the base coat horses because the contrasting darker color color, which the gray gene eventually gradually fades away. Because the gray (G) turns white. A gray foal can sometimes gene is dominant over all the genes dis- be determined by white rings in their hair cussed so far, it will eventually turn all other coats and around their eyes. This is often the coat colors—dun, roan, bay, black, buck- beginning of the graying process, which skin, champagne, dun, palomino, roan and varies from horse to horse. The graying sorrel—white. process may occur over several years or a However, the gray gene does not affect lifetime. The tail of a gray horse may also the white hair on the horse’s body that become whiter or remain dark. is created by Paint Horse pattern genes, In addition to its variable process, the gray such as tobiano or overo, or white that gene creates many shades and patterns, occurs as a blaze, stocking or other mark- including primitive markings, dapples (round, ing. These white markings remain visible shaded spots) and “fleabitten” coats (flecks percent of the time. Heterozygous grays even as the gray horse becomes whiter- of color dispersed throughout the body). It is produce gray foals 50 percent of the time. looking with age. still unknown which genes control the shades Unfortunately, both homozygous and het- Because gray horses do become whiter and patterns of grays and the speed of the erozygous grays are prone to melanomas with age, they are sometimes confused with graying process. Therefore, the idea that a (skin tumors). These tumors commonly the white horse. The difference is that a homozygous gray (GG) will turn white faster occur beneath a gray horse’s tail and around mature gray horse may appear white, but than a heterozygous gray (Gg) is unproven. its ears. Fortunately, though they can be has dark eyes and dark skin. A white horse What is known is that homozygous grays unsightly and disfiguring, only about 5 per- also has dark eyes but has pink skin. do exist and they produce gray offspring 100 cent of these melanomas are malignant.

White Horses In most breeds, including Paint Horses, white gene may mutate to the dominant is impossible to know what color of dark true white horses are rare. Keeping this in form, creating a white foal. The white foals foals it will produce unless you have exten- mind, it may seem unusual to learn that the that resulted from these matings went on to sive knowledge of the horse’s color pedi- white gene (W) is dominant over all other breed as if they carried the W gene. This gree.) The other 25 percent of the foals coat colors, including gray. This means that may suggest that the white allele has a high produced from a white-to-white mating are any foal receiving one dominant white gene spontaneous mutation rate. lethal. These homozygous white foals (WW) will be white. According to the Punnett Square, a white are usually resorbed during gestation. White foals are born white and have dark horse mated with a dark-colored horse will However, these homozygous white foals eyes and pink skin, which eventually distin- produce a white foal 50 percent of the time. are not genetically like foals that have Overo guish them from a gray horse. If they have a Mating two white horses results in 50 per- Lethal White Syndrome, which results from Paint Horse coat pattern, it is not identifiable cent white foals and 25 percent dark foals. an overo-to-overo mating. because the markings blend in with their hair (Before a white horse produces offspring, it coat, unlike perlinos and cremellos, which have visible patterns and blue eyes. Distinguishing Differenced Between White and APHA has included the white color on Cremello/Perlino Horses CR its registration form for some time. ApHC White (W) Cremello/Perlino (CR ) and the Jockey Club also list white as a birth color white cream to white registerable color, but it is extremely rare in eye color dark blue both breeds. skin color pink pink Even though the white gene is known to be dominant, it is still somewhat of a mys- visibility of not visible tery to scientists because two dark-colored white markings visible parents have been known to produce a genetic base coat any genetic sorrel or chestnut for cremello, white foal. To explain this, researchers have combination bay for perlino concluded that a dark-colored parent carry- color production produces 50% white horses produces 100% palomino or ing the recessive white gene (w) can pass a potential regardless of mate’s color buckskins, depending copy of this gene to their offspring. Once on genotype of mate inherited by the unborn foal, the recessive

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Overo Lethal White Syndrome A Lethal White is a foal of overo lineage, born all white or mostly white. The foal may seem normal at birth, but usually begins show- Lethal Whites—Fact Versus Fiction ing signs of colic within 12 hours because of a non-functioning According to researchers at the University of Minnesota, colon. Because the syndrome is always fatal, lethal white foals are there are three issues that may account for the fact that we often euthanized. do not see 25 percent of all overo-to-overo crosses pro- This condition, referred to as Overo Lethal White Syndrome ducing lethal whites: (OLWS), is always fatal, and results in both emotional and economic 1. Not all lethal white foals survive to birth. Some are loss to breeders. resorbed or aborted by the mare. 2. Not all lethal white foals that are born are reported. Occurrence of Lethal White Syndrome 3. Not all patterns that are currently classified as overo, The body of all living things is made of protein, minerals and water. such as sabino or splashed white, are lethal when The proteins comprise a large proportion of the body’s structure, and homozygous. also regulate body functions by acting as hormones and enzymes. In addition, many myths cloud the truth regarding lethal The building blocks of proteins are amino acids, and the function of white syndrome. Below, the University of Minnesota Equine the protein is dependent on the order of the amino acids. The order of Genetics Group dispels nine of the most common myths. the amino acids is determined by DNA, which codes for the composition of the body, its growth and function. 1. Myth: All overo horses are carriers of the The code for inherited conditions such as OLWS is in the DNA, and lethal allele. therefore its composition must be determined before it can be known Fact: There are many overos that do not carry how it causes disease. the lethal allele. Similar to how a protein is made of amino acids, DNA is made of bases. These bases are arranged in triplets that code for the amino 2. Myth: Twenty-five percent of foals from two overo acids. parents will be lethal whites. When the base pairs change (through mutation) and cause an amino Fact: Because there are overos that do not carry the acid substitution, the function of the protein coded is altered. The allele, the incidence of lethal white syndrome is less alteration of protein function causes genetic traits, including disease. than 25 percent in overo-to-overo matings. Causative genes are responsible for similar conditions in other 3. Myth: Registered tobianos, Solids or Paint crosses species, so research to determine the order, or sequence, of base pairs cannot carry the lethal allele. and the resulting amino acids for two “candidate genes” is crucial to Fact: There are tobianos that have overo bloodlines, understanding OLWS. and these horses can be carriers of the lethal allele. Solids and Paint crosses can carry the lethal allele. Finding the Lethal Allele Based on studies by the University of Minnesota’s Equine Genetics 4. Myth: Totally white Paints are not carriers of the Group and Portland University, it has been concluded that OLWS foals lethal allele. have two lethal alleles (L/L); their parents have one normal and one Fact: These white horses are often carriers of the lethal allele (N/L), and solid-colored horses of other breeds have two lethal allele. copies of the normal allele (N/N). 5. Myth: All totally white foals born to two overo parents This is strong evidence that the gene mutation detected is responsi- are lethal whites. ble for OLWS. To date, researchers have tested almost 1,000 horses, Fact: There are totally white Paints that are not affect- and the results are consistent. ed by the lethal white syndrome.

Proving the Lethal Theory 6. Myth: Mares cannot produce lethal foals in It appears that all overo horses are not the same, at least for this consecutive years. gene. Overos can carry either (N/N) or (N/L). Researchers have not Fact: The genetic makeup of one foal does not affect found a living adult horse that has two copies of the lethal sequence subsequent births. (L/L), and they have tested several all-white Paints. The geneticists have found carrier horses in overos, tobianos, 7. Myth: Only one parent determines if a foal will be a toveros, Solids, crop-out Quarter Horses and Pintos. The discovery of lethal white. the Lethal allele in Pintos is important in limiting the spread of this Fact: Both the sire and the dam contribute a copy of mutation, because many Pinto breeders are unfamiliar with OLWS and the lethal allele. the gene is now making its way into other breeds that are crossing onto 8. Myth: Crop-out Quarter Horses cannot carry the Pintos for color production. lethal allele. By taking the lead in the investigation of OLWS, APHA has provided Fact: A small number of crop-outs have been tested valuable information to all breeders. and found to be carriers of the lethal allele.

Genetics in Overo Lethal White Syndrome 9. Myth: You can reliably tell the carrier status of a Paint In the past few years, Lethal White Syndrome has been heavily exam- by their color pattern. ined from a genetic standpoint. In 1997, APHA approved a grant to the Fact: This is false.

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University of Minnesota to support a research References study aimed at locating the gene responsible Bowling, Dr. Ann T., Veterinary Genetics Laboratory, University of for OLWS and developing a test to determine California-Davis School of Veterinary Medicine. Interview by Kim the disease. Guenther. Led by Dr. James Mickelson, Dr. Stephanie Bowling, Dr. Ann T., “Dominant Inheritance of Overo Spotting in Paint Valberg and Dr. Elizabeth Santschi, the Horses,” The Journal of Heredity Volume 85, No. 3 (May/June 1994). research has now identified the gene that is Duffield, Dr. Debbie, and Dr. Peg Goldie, Spotted Horse Research associated with OLWS and is likely responsi- Group of Portland State University, Oregon. Interview by Kim ble for the condition. Guenther. Researchers are still working to more com- Evans, J. Warren, Anthony Borton, Harold Hintz, and L. Dale Van pletely describe the inheritance of overo and, Vleck. The Horse. Second edition. New York: W. H. Freeman and more than ever, it is clear that overo horses Company. are at risk of carrying the OLWS gene. Fio, Lauri, “The New Genetics of Overo,” The Horse Report Volume 12, Fortunately, horse breeders can now test No. 2 (October 1994). their stock for the presence of this gene and Guenther, Kim, “Predicting Color,” Parts 1-3, Paint Horse Journal use this information to assist in making mat- Volume 29, No. 1 (January 1995): 48-54; No. 2 (February 1995): ing decisions. This test allows breeders to 48-54; No. 3 (March 1995); 82-87. positively identify horses that are carriers of Holmes, Frank, “A Lighter Shade of Red,” Paint Horse Journal Volume the gene and to find new pedigree sources 32, No. 12 (December 1998): 72-80. for their color breeding programs. Holmes, Frank, “The Mystery of Tovero,” Paint Horse Journal Volume 31, No. 12 (December 1997): 130-139. Testing for Lethal White McCall, Dr. Jim and Lynda, “The ABCs of Coat Color Genetics,” Parts 1- The diagnostic test for the overo gene 4, Paint Horse Journal Volume 33, No. 12 (December 1999): 82-85; uses a process known as ASPCR (allele spe- Volume 34, No. 1 (January 2000): 92-95; Volume 34, No. 3 cific Polymerase Chain Reaction). The test (February 2000): 76-79; Volume 34, No. 4 (March 2000): 78-83. can be performed from either blood or hair Ramsbottom, Ann, “Understanding Tobiano Genetic Markers,” Paint samples with roots (hair preferred). The test Horse Journal Volume 24, No. 1 (January 1990): 54-55. identifies a specific mutation site in the Sponenberg, Dr. D. Philip, “A Sabino Case in Point,” Paint Horse Journal DNA sequence that has been shown to be Volume 32, No. 12 (December 1998): 81-83. associated with Lethal White overo foals. Sponenberg, Dr. D. Philip, “The Genetic Equation,” Parts 1-8, Paint Researchers know of no other mutations Horse Journal Volume 28, No. 1 (January 1994): 12; No. 2 (February that are associated with Lethal White overo 1994): 12; No. 3 (March 1994): 12; No. 4 (April 1994): 12; No. 5 horses. However, owners requesting the (May 1994): 12; No. 6 (June 1994): 12; No. 7 (July 1994): 12; No. 8 diagnostic test should be certain to under- (August 1994): 12, 50. stand that there is the rare possibility that Sponenberg, Dr. D. Phillip, and Bonnie V. Beaver. Horse Color. College two NN horses could have a Lethal White Station: Texas A&M University Press, 1983. foal, due to the sire and dam having in com- Vrotsos, Paul D. R.V.T., and Elizabeth M. Santschi D.V.M., “Stalking the mon a mutation at a site other than the one Lethal White Syndrome,” Paint Horse Journal Volume 32, No. 7 (July detected by this test. 1998): 500-502. Walker, Dawn, “Lethal Whites: A Light at the End of the Tunnel,” Paint Performing the Test Horse Journal Volume 31, No. 2 (February 1997): 114-119. The test for the lethal form of the gene associated with OLWS is available from two If you would like to learn more about equine color genetics, universities. some suggested readings are: All tests require hair samples be pulled Equine Color Genetics by Dr. D. Phillip Sponenberg. Published by Iowa from the mane or tail with the roots intact. State University Press in 1996. To order a copy, call (800) 862-6657. The number of hairs required ranges from Horse Genetics by Dr. Ann T. Bowling. Published by Oxford University 15-30. Hair samples can be sent in a regular Press in 1996. To order a copy, call (800) 445-9714. envelope. All samples must be clearly identified with the horses’ registered name, number and other required information. A copy of the registration papers should be enclosed with the sample whenever possible. Test results will be mailed to the owner or veterinarian, whomever is specified on the form. Results will not be given by phone. Arrangements for testing can be made through APHA. Contact Field Services for forms and instructions.

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COLOR DESCRIPTIONS

BLACK GRULLO Entire coat, including muzzle, flanks and A form of dun with body color smoky or legs, are black; color may fade when exposed mouse-colored (not a mixture of black and to the sun; could have rusty tinge during cer- white hairs, but each hair mouse-colored; tain times of the year; early foals may be an mane and tail black; has black primitive overall mousy gray, then shed to black. markings.

BROWN DUN Body color brown or black, with light areas Diluted body color of yellowish or gold; at muzzle, eyes, flank and inside upper legs; mane and tail are black or brown; has black mane and tail usually black. or brown primitive markings.

CHESTNUT BAY Body color dark red or brownish red; range Body color reddish brown, with variations from very light to liver chestnut; liver chest- ranging from dark blood bay to light bay and nut can be distinguished from black or usually distinguished by black mane and tail, brown only by the bronze or copper high- ear tips, lower legs. lights on the legs; mane and tail usually dark red or brownish red, but may be flaxen.

BUCKSKIN SORREL Body color yellowish or gold, mane and tail Body color reddish or copper-red; mane and black; black on lower legs; lacks primitive tail usually same color as body, but may be markings. flaxen or very dark brown.

BLUE ROAN PALOMINO The overall intermingling of white hairs with Diluted body color varying from rich gold a black body color; head, lower legs, mane to pale yellow; mane and tail generally pale and tail are usually solid or darker; does not or off-white but may be same color as body get progressively whiter with age. (with nonblack points).

BAY ROAN CREMELLO The overall intermingling of white hairs with Double dilute of chestnut/sorrel resulting in bay body color; head, lower legs, mane and body color, mane and tail of cream or off- tail are usually solid or darker; does not get white with pale, pinkish skin; the coat has progressively whiter with age. enough yellow hue to allow white markings to be visible; eyes are blue or amber. GRAY Dominant over all other color genes; born RED ROAN any color with white hair progressively turn- The overall intermingling of white hairs with ing the coat whiter as the horse ages; dark chestnut/ sorrel body color; head, lower legs, skin; normally grays first around eyes and mane and tail are usually sorrel or dark red; behind ears. does not get progressively whiter with age. PERLINO Double dilute of bay/brown resulting in body RED DUN color of cream or off-white; lower legs, mane A form of dun with body color yellowish or and tail light rust or chocolate shade; skin is flesh-colored; mane and tail are red or red- pinkish or grey; eyes are blue or amber; the dish; has red or reddish primitive markings. coat has enough yellow hue to allow white markings to be visible.

American Paint Horse Association Post Office Box 961023 • Fort Worth, Texas 76161 (817) 834-APHA (2742) • FAX (817) 834-3152 • apha.com