APHA Color Guide - Press

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ContentsThe Genetic Equation of Paint Horses . . . . . . . . .IFCTobiano . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1Overo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1Tovero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3Breeding the Tobiano Paint . . . . . . . . . . . . . . . . . . .4Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Understanding Simple Dominance . . . . . . . . . . . . .4Using the Punnett Square . . . . . . . . . . . . . . . . . . . .4Understanding genes, simple dominance

and the Punnett Square . . . . . . . . . . . . . . . . . . . .4Breeding the Tobiano Paint . . . . . . . . . . . . . . . . . . .5Determining Tobiano Homozygosity . . . . . . . . . . . .5Breeding the Overo Paint . . . . . . . . . . . . . . . . . . . . .6Breeding the Frame Overo . . . . . . . . . . . . . . . . . . . .6Defining Minimal-White Frame Overo . . . . . . . . . .6Breeding the Splashed White Overo . . . . . . . . . . . .6Defining Minimal Splashed-White Overo . . . . . . . .6Breeding the Sabino Overo . . . . . . . . . . . . . . . . . . .7Defining Minimal-White Sabino Overo . . . . . . . . . .7Breeding the Tovero . . . . . . . . . . . . . . . . . . . . . . . . .7Coat Colors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8The Basic Rules of Coat Color Genetics . . . . . . . . . .9Overo Lethal White Syndrome . . . . . . . . . . . . . . .16Lethal Whites—Fact Versus Fiction . . . . . . . . . . . .16References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17Color 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 breedsbecause of their spotted coat patterns. Their base coatsare the same colors as those of other breeds, but super-imposed over these colors are a variety of white spottingpatterns. The three patterns recognized by APHA aretobiano, overo and tovero.

The ability to recognize these patterns and under-stand the genetics behind them is essential for PaintHorse breeders. Being knowledgeable about coat pat-terns helps breeders and owners accurately describetheir horses. Understanding the genetics that producethese patterns helps breeders increase the proportion ofspotted horses in their foal crops.

Following are descriptions of the major Paint Horsespotting patterns.

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The second generally accepted type ofspotting is overo (pronounced: oh vair´ oh).Knowing the history behind the term overomay be helpful in understanding the some-what confusing situation of having multiplepatterns with one name.

Overo is a Spanish word, originally mean-ing “like an egg.” In this case, it refers tospeckling or spotting. Long ago, in SouthAmerica, the term overo was used for all thevarious spotting patterns in horses: tobiano,overo (all three types) and also the blanketand leopard patterns typical of Appaloosas.In Argentina, the word overo is still used todescribe all the different spotting patternsother than tobiano.

In the United States, overo is usually usedto mean “Paint, but not tobiano.” This hasresulted in the lumping together of three

different spotting patterns under one name,and the result can be confusion in breedingprograms.

The term overo covers three geneticallydistinct patterns: frame overo, sabino andsplashed white.

Frame OveroThe name “frame” refers to the usual

appearance, which is of white patches cen-tered in the body and neck, and framed bycolored areas around them.

The usual frame pattern has a horizontalarrangement and does not cross the topline,as does tobiano. The overo’s head is usuallyquite extensively marked with white and theeyes are commonly blue.

The feet and legs of frame overos are usu-ally dark, although white feet and minor

The first major pattern is tobiano (pro-nounced: tow be yah´ no). The name tobianois itself unusual and has an interesting history. In Argentina, it is the habit to nameunusual colors after horses or people whoconnect the color to a specific event or indi-vidual. In the case of the tobiano horse, thatevent was the rescue of Buenos Aires byBrazilian General Tobias during a militaryaction that took place in the 1800s. Many ofthe troops with Tobias were mounted ontobiano spotted horses from Brazil.

This color pattern had occurred only rarelyin Argentina before this event (and waslumped in with all the other spotting patternsas overo), but became firmly associated withTobias and his troops afterwards, ending uptaking his distinctive name.

The tobiano pattern occurs in manybreeds worldwide. It is common in ponybreeds, some draft breeds and evenoccurs in some of the warmblood breeds.In some breeds, tobiano spotting disquali-fies a horse for inclusion in the registry—this in spite of the fact that the trait mayhave been present in some of the founda-tion horses from which the breed sprang.

The characteristics of tobianoA tobiano’s feet and varying portions of

its legs are usually white, the head usuallyhas no more white than normally found ona non-spotted horse, and the spots usual-ly cross the topline somewhere betweenthe ears and tail.

Tobiano spots are typically crisply delineat-ed from the colored areas and have a vertical

arrangement. A tobiano’s eyes are usually dark.

These horses can vary from quite dark, with only small amounts of white, to quite white, with littleremaining color. The darker individuals some-times have so little white spotting that theymay be confused with nonspotted horses.

Minimally spotted tobianos are interest-ing because they are essentially tobianosthat did not get spots. These horses willproduce just like a spotted horse, however,and that is the reason the pattern may“mysteriously” appear in a breeding pro-gram for solid horses.

A clue to identifying these “nonspottedtobianos” is that they tend to have a largeamount of white on the lower legs but littlewhite on the head. This combination is oth-erwise rare because it is usually the casethat non-spotted horses with a great dealof white on the head have a large amountof white on the feet, and vice versa.

In the middle portion of the range oftobiano spotting there is no problem tellingtobianos from other Paint patterns. They arequite distinctive. At the whitest extreme,many tobianos are all white except for a col-ored head. This pattern is sometimes called“Moroccan,” although the connection to thecountry of Morocco or its horses is tenuousat best.

Other details of the tobiano pattern includethe fact that on many of these horses, theborder between the white and colored areasconsists of pigmented skin overlaid by whitehairs. The result is usually a bluish cast to

the border, almost like a halo or a shadow.Another peculiarity of some tobianos is thepresence of “ink spots” in the white patch-es. These spots are small and generallyround in shape.

APHA Coat Color Genetics Guide • 1

Tobiano

Overo

Typical Tobiano Patterns

Typical Overo Patterns

Tobiano

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white leg marks are as common on frameoveros as they are on nonspotted horses.The white areas on frame overos are usual-ly crisply and cleanly delineated from thecolored areas, although some have a halo orshadow of pigmented skin under white hairdirectly at the boundary.

The frame overo pattern occurs in a lim-ited range of horse breeds. It seems toappear only in breeds that have Spanishancestry, including the Paint Horse.

The genetics of frame overo has onlyrecently been documented. Frame overobehaves as a dominant gene. It is commonto mate frame overo horses to nonspottedhorses, and about half of the resulting foalsare spotted.

On many occasions, though, there arerecords of frame overos being produced bytwo nonspotted parents. This is typical of arecessive gene, and it is not logical to haveboth a recessive and a dominant controlover the same pattern.

Some of these horses are genetically frameovero, but have failed to get a body spot. Theyare essentially very dark frame overos—sodark that the spots are all gone from the body.They still have the gene, however, and can stillproduce frame overo-spotted offspring.

At the whiter extreme, frame overo is thepattern most closely associated with OveroLethal White Syndrome (see page 16).

Recent characterization of the generesponsible for lethal white foal syndromehas confirmed that foals with two doses ofthe lethal white gene are white and die soonafter birth from gut innervation abnormali-ties. Horses with only one dose survive.

This documentation is important forPaint Horse breeders. With DNA tests nowavailable to identify the lethal white gene, itis possible to test breeding horses. Those

with the gene can bemated to horses with-

out it, resulting infoals that are about

half carriers and half-non-carrier foals, but avoiding completely

the production of lethal whites.

Sabino OveroIn literal Spanish, sabino (pronounced:

sah bee´ no) means pale or speckled. InEurope, and increasingly in the UnitedStates, sabino is used to describe a uniqueand interesting pattern of white spotting inhorses.

Sabino horses usually have four white feetand white legs. The white usually extendsup the legs in ragged patches, and thenextends onto the horse’s body from the belly.The head is usually fairly white and the eyesare commonly blue.

Many sabino horses have partially blue,partially brown eyes. Flecks, patches androan areas are common on sabinos, in con-trast to the frame overos, which are usuallymore crisply marked.

Sabino occurs in a large num-ber of breeds worldwide,including Paints, Thorough-breds and Clydesdales. The pat-tern is commonly the cause ofspotted foals that appear inbreeds that frown on them, suchas the British pony breeds andthe Quarter Horse.

The sabino pattern is also agreat imitator, and some of thesehorses are nearly perfect mimicsof tobiano or frame overo. Whenthe sabino pattern is minimally expressed, the horse usual-ly has four white socksand a blaze. Usuallythere is some betrayalof the fact that theseare not the usualwhite marks on horses,due to some ragged edge or long, narrow extension up the leg.

Some sabinos also have odd white patch-es on the knee or hock, removed from themain portion of the lower white mark. Afew sabinos do have a dark foot or two,although most have four white feet.Minimally marked sabinos are easily con-fused with truly nonspotted horses.

In the middle range of expression, sabinohorses are fairly distinctive and are usuallydifficult to confuse with other patterns.

Most have white extending from the bellyand have roan and flecked areas in additionto white areas. However, a few will be near-ly entirely roan without patches of white.These could be confused with true roanhorses, although the facial and leg whiteusually gives these away, and they do nothave dark heads typical of true roans.

Another extreme is the sabino that ispatched, but not roaned. Sabino horses caneasily be confused with frame overos, espe-cially if they have one or two dark feet. Mostpatched sabinos have smaller, more raggedpatches than is typical of frame overos. Insome cases, it is impossible to distinguishbetween horses that are truly sabinos andthe frame overos that also happen to havewhite markings on their feet in addition tothe frame overo pattern.

The whitest of the sabinos are nearly orentirely white. Some retain color only on theears and others are white all over. One ofthe whiter ranges of expression includescolor on the ears, chest and tail base. Theseare the Medicine Hat Paints that were prized

2 • APHA Coat Color Genetics Guide

Frame Overo

Splashed White

Sabino


While each of the Paint patterns—tobiano, frame overo, sabino and splashed white—can mark a horse on its own, many horses sportcombinations of these. When these patterns combine, the result is a horse with a pattern that can sometimes be difficult to classify.

When a mating between a tobiano and anovero produces an offspring that exhibitscharacteristics of both patterns, APHA recog-nizes the resulting pattern as tovero (pro-nounced: tow vair´ oh). (It should also benoted that, while considerably rarer, a crossbetween a tobiano and a solid can also pro-duce a tovero.)

In this instance, the combined patterns pickup the white from each of their individual com-ponents. They are then genetically mixed tocreate a combination pattern on the horse’scoat. For instance, a horse with a frame overosire might inherit a white framed area on eachof its sides. If the horse had a tobiano dam, itmight inherit a white, blanket-like pattern thatcovers its entire back. The result might looksomething like the tovero shown on this page,which is mostly white.

Many of the combinations are called toverobecause most are tobiano plus one of theother patterns.

Although the word tovero has been a partof APHA’s vocabulary from the onset of theregistry, it remains to this day somewhat of anambiguous term.

Just as there are extremes within thetobiano and overo coat patterns—from most-ly dark to mostly white—so are there extremeswithin the tovero pattern.

At one end of the spectrum—the mostly darkone—are those toveros that closely resembletobianos except for their face markings, whichshow an overo influence. At the opposite end—the mostly white one—are those toveros whoseonly dark pigmentation might appear aroundthe ears, eyes or chestnuts.

In between those two extremes is the horsethat can be termed the “typical” tovero, dis-tinguished by the four basic coat characteris-tics shown below. Typical toveros have:1. Dark pigmentation around the ears, which

may expand to cover the forehead and/oreyes.

2. One or both eyes blue.3. Dark pigmentation around the mouth,

which may extend up the sides of the faceand form spots.

4. Chest spot(s) varying in size. These mayalso extend up the neck.

5. Flank spot(s) varying in size. These areoften accompanied by smaller spots thatextend forward across the barrel and upover the loin.

6. Spots, varying in size, at the base of the tail.Identifying the tovero pattern is not an easy

task. During the Association’s early years,some toveros were mistakenly classified astobianos or overos. In defense of the peoplewho misclassified those animals, two pointsmust be made. First of all, during the registry’sinfancy, the pattern was much rarer than it isnow. There simply weren’t enough toverosbeing registered to establish a workable pro-file of what their physical characteristics were.

Second, it had not yet been firmly estab-lished how these horses would breed—whatpatterns they would produce that would proveor disprove their classification.

More than 40 years of Association growthhas alleviated both of these conditions, andthe APHA Registration Department now hasthe situation well in hand.

Tovero

Typical Tovero Patterns


by the Native American tribes ofthe Great Plains. Most sabinos thatare largely white are very speckledand roaned, and some can be con-fused with Appaloosas.

Some sabinos are quite whiteand survive, which points to thisbeing entirely different from theovero that results in lethal whitefoals when homozygous. Sabino,by itself, is not associated withlethal white foals.

Splashed White OveroSplashed white is the least com-

mon of the spotting patterns,although it is increasing in frequen-cy as breeders use more splashedwhite horses in their breeding pro-grams.

The pattern usually makes thehorse look as though it has beendipped in white paint. The legs areusually white, as are the bottomportions of the body. The head isalso usually white and the eyes arefrequently blue.

The edges of the white are typi-cally crisp and clean, with no roan-ing. Some splashed whites havedark toplines, but on some thewhite crosses the topline.

Recent genetic evidence suggeststhat the splashed white pattern iscaused by a dominant gene,because splashed white foals haveresulted from splashed white tonon-splashed white matings.

Some people have observed thatmany splashed white horses aredeaf. This is not much of a problemif the trainer realizes the limitationsof the horse in question and modi-fies the training program to meetthe horse’s special needs. Many ofthese horses go on to lead normaland productive lives.

Because no homozygoussplashed white horses have everbeen documented, researchers sus-pect that this is another gene thatcannot exist in homozygous form.If this is true, the loss of hearingprobably occurs early in gestationrather than at term. Because of this,the best strategy for producingsplashed white horses is to matethem to horses without thesplashed white pattern.

Tovero



Before you begin breeding for color, thereare a few basic genetic concepts you shouldunderstand. Though genetics can seemdaunting at first, by understanding genesand simple dominance, and knowing how touse the Punnett Square, any horse ownercan plan their color breeding program withconfidence.

GenesGenes are the basic units of inheritance.

Genes are linked to form a chromosomesimilar to the way pearls are threadedtogether to make a strand. Each particularspecies has a specific number of chromo-somes (64 for the horse), and each chro-mosome has a duplicate mate.

Each gene on the chromosome has amate, or allele, in exactly the same place, orloci, on each of the chromosome’s matchedpair. Basically, each pair of genes codes fora specific job. A pair of genes can controlsomething as obvious as whether or not acow will have horns, or it may be as subtleas coding for a specific portion of a bimole-cular molecule, or controlling the function ofother genes.

During the cell division in which one celldivides into either two egg or two spermcells, only one member of each chromo-some pair goes into each new cell. Thisprovides every sperm and egg with onlyone copy of each gene. Upon fertilization,every chromosome, and therefore everygene, is reunited with its correspondingmate to create a unique individual.

In coat color genetics, one of the goals isto identify the possible genes in the parents

and predict the probability of coat colors intheir offspring. To help keep track of thegenes whose function is thought to havebeen identified, geneticists assign a letterof the alphabet to the pair.

Understanding Simple DominanceGene interactions can be complex and

confusing. Fortunately, some genes adhereto a relationship based upon simple domi-nance. Within this framework, there are twobasic expressions of the same gene—onedominant, one recessive. The recessiveform of the gene is submissive to the dom-inant form. The recessive gene is expressedonly when both copies of the gene are in therecessive form.

Capital letters usually indicate dominantgenes. Lowercase letters indicate recessivegenes. This system is complicated by theuse of superscripts. For example, the dom-inant form of the gene creating palomino isCCcr. The recessive is referred to as C.

Regardless of the letters used, eachindividual obtains one copy of the genefrom each parent. In the system of simpledominance, this pairing occurs in one ofthree ways:

Homozygous dominant—In this instance,both alleles are in the dominant form, asindicated by a capital letter, for example,AA. The color determination is under thecontrol of the dominant gene, and all off-spring created from this individual can onlyreceive a copy of the dominant gene.

Homozygous recessive—Here, bothcopies of the allele are in the recessiveform, for example, aa. The color determi-

nation is under the control of the recessivegene, and in many cases this means thereis no expression.

For example, the recessive form of thegene for roan (Rn+), palomino (C), gray (g),tobiano (to) and dun (Dnnd) allow the bodycoat to be expressed by the dominant gene.

Foals with a homozygous recessive par-ent will receive one copy of this parent’srecessive gene.

Heterozygous—One member of the pairis dominant, while the other is recessive, forexample, Aa. The dominant form is in con-trol of the expression. Offspring have a 50-50 chance of inheriting either the dominantor the recessive gene.

Using the Punnett SquareA Punnett Square is a simple way to pre-

dict the possible genetic combinations fromthe mating of two individuals. To use this tool,first draw a square. Across the top, list thegene combination of the stallion. Down theleft side, list the gene combination of themare. Then, bring one value from each parentinto the corresponding box within the square.

Each box represents a 25 percentchance of a specific gene combination. Inthe example above, foals from this crosshave a 50 percent chance of getting the Aacombination and a 50 percent chance ofgetting the aa combination.

Stallion (aa) Mated to Mare (Aa)Stallion

a aA Aa Aaa aa aa

Mare

Understanding genes, simple dominance and the Punnett Square


The tobiano pattern is under the controlof the dominant gene TO. The most com-mon genotype for the tobiano is the het-erozygous TOto. Fifty percent of the foalsproduced from a heterozygous tobianoshould have the tobiano pattern.

Fortunately, the homozygous tobianoTOTO exists. Having two copies of thetobiano gene does not increase the amountof white on the horse, but individuals carry-ing this rare genotype can often be identi-fied by small dark hairs scattered in clustersin the white areas of the coat. Not allhomozygous tobianos have these “ink spots”or “paw prints,” nor do these markingsoccur only in homozygous horses. However,there is a strong association between thispattern and the TOTO individual.

Homozygous tobianos are beneficial tobreeding programs due to their ability toproduce tobiano offspring. Statistically,every foal produced from the mating shouldreceive one copy of the dominant tobianogene TO, thus creating a tobiano.

Occasionally, a homozygous tobianomating produces a solid-looking horse.This horse carries the tobiano gene but hasonly limited white markings. These horsesare often referred to as minimal-whitetobianos.

For these horses, the tendency of thetobiano to have a dark head and white legsholds true. The head may be completely darkor have very little white on it. However, thelegs will show the specific characteristics.

According to the late Dr. Ann Bowling inher book Horse Genetics, minimal-whitetobianos have dark spots or streaks in thewhite markings extending up from the coro-net. Also, the white extending over thehocks ends as a horizontal line.

As of this time, there has not been a caseof a minimal-white tobiano that has failedto have white leg markings.

Even though these horses are registeredby APHA as solid Paints, they are, in fact,tobianos and do pass on the dominanttobiano gene 50 percent of the time.

Homozygous tobianos result from themating of two tobiano parents. Accordingto the predictions of the Punnett Square,one out of every four foals produced by twoheterozygous tobiano parents should be ahomozygous tobiano.

Some Paint Horse breeders disagree withthe Punnett Square projections, maintain-ing that the TOTO gene combination isharder to obtain. They also believe that a

homozygous tobiano ismore likely to be pro-duced if both tobiano par-ents come from tobianoparents.

Currently, there is not a laboratory test to identify thetobiano gene. Homozygoustobianos are identified on thebasis of other genetic evidence.

To qualify as a homozygoustobiano, a horse must be theresult of a breeding of twotobiano parents. The horse should have a characteristic tobiano pattern,including ink spots, and a pedigree andbreeding record that indicates homozygosi-ty for the tobiano pattern.

According to the Punnett Square, ahomozgyous tobiano stallion mated to aheterozygous tobiano mare should produce50 percent homozygous foals and 50 per-cent heterozygous foals. No offspringshould be solid.

Determining Tobiano HomozygosityBreeding a homozygous tobiano should

produce all tobiano foals, with the excep-tion of a rare minimal-white. A horse thatproduces five tobianos out of five solidmates is thought to have a 97 percentchance of being homozygous. Seventobianos from seven solid partners increas-es the odds to 99 percent. Ten tobiano off-spring from 10 solid mates increases theodds to 99.9 percent.

In addition, genetic marker analysis isused to try to identify homozygous tobianos.This analysis is similar to playing the gameClue. Certain facts are given, and then by theprocess of elimination one tries to determinewhich parent or parents supplied thetobiano gene. Remember, the horse musthave been produced from the mating of twotobianos. Tovero parents do qualify.

The tobiano gene is linked to a gene unitcomprised of the E gene (see page 12), theRn gene (see page 17), and two other genes,ALB and GC, that code for blood proteins.These four genes lie so close together on thesame chromosome that they are usually

passed on as a unit to the next generation,making their presence an important clue todetermining a tobiano’s homozygosity.

This fact creates the opportunity to tracemovement of the tobiano gene.

The ALB blood protein comes in twoforms—A or B—while F and S are the sym-bols given to the two forms of the GC gene.A major clue to determining tobianohomozygosity is that 90 percent of thetime, the tobiano gene is associated withthe B form of the AL gene and S form of theGC gene.

The blood test that is currently used inthe search for the homozygous tobianodetermines which form of the AL and GCgenes a particular horse has.

And don’t forget that the expression of theE provides a color trace for the tobianogene, as well. This means that the tobianogene lies close to the gene that determineswhether the base color of the horse is red orblack—e or E, respectively. The goal is todetermine which form of the E gene islinked to the TO.

(The roan gene, which is in the E Rn ALBGC unit, appears to commonly exist in therecessive form Rn+. It is extremely rare tofind a roan tobiano.)


Homozygous Stallion (TOTO) Matedto Heterozygous Mare (TOto)

StallionTO TO

TO TOTO TOTOhomozygous homozygous

to TOto TOtoheterozygous heterozygous

Mare

Breeding the Tobiano PaintTobiano



Breeding the Splashed White OveroAccording to Dr. Bowling’s work, the splashed white pattern is under the con-

trol of a dominant gene identified by the letters Spl. At this point, there has notbeen a documented mating of two splashed white overos creating a homozy-gous individual.

Defining Minimal Splashed-White Overo• A great deal of

white on the face.

• Solid bodies, perhaps with a small white spot on the belly.

• White leg markings.These horses may be registered as

Solid Paint-Bred, but in reality they are overos and will produce overos 50 percent of the time.

Breeding the Overo PaintLittle is known about the genetics that create

overo patterns. It is commonly accepted thatovero patterns are under the influence of one ormore dominant genes. It appears that each of thepatterns may be the result of a dominant gene,but it is also possible that there is only one geneand that gene modifiers change the pattern.

There is also some evidence that the genesthat produce leg and facial markings may influ-ence the amount of white on an overo. Thisappears to be true for the sabino and splashedwhite patterns.

The frame overo, like the tobiano, is thoughtto be less sensitive to these genes.

Time and research will eventually answerthese questions. For now, here is what the threeovero patterns seem to have in common.

All the overo patterns have a large range ofexpression. At one end, they appear mostlywhite. At the other end, a minimal-white overomay be hard to distinguish from a solid horse.

These minimal-white overos may be the reasonthat so many breeders think that overo appears atrandom from solid horses. It may also be the rea-soning behind the belief that it is easier to get anovero by breeding an overo to a solid that has anovero parent. These overo breeding stocks maybe minimal-white overos.

The development of a test to determine thepresence of the overo gene(s) will go a long waytoward sorting out this confusion.

The possibility of there being a homozygousovero does not look good. It is thought that thehomozygous overo is plagued by the lethalwhite syndrome. Lethal white foals die shortlyafter birth due to lack of proper developmentof their digestive systems.

There have been cases of lethal white syn-drome occurring from the mating of an overoto a solid. Because of this, the questionbecomes: Were these solid horses minimal-white overos carrying an overo gene and there-fore producing a homozygous overo foal, or isthere some other gene action associated withthe overo that occasionally produces foals withthe lethal white syndrome?

To confuse the matter further, each overopattern has the ability to produce nearly whitenormal foals. This is not to say that these foalsmay not be plagued by some of the other prob-lems associated with mostly white horses.There is some evidence that deafness mayoccur more often in nearly white horses. Andwith age, the pink skin around the eyes of awhite horse quite often develops cancer.

In spite of the similar action of the hypothe-sized overo genes, each type of overo has acharacteristic pattern.

Frame overos range from being nearly totally white to the minimal-white indi-vidual. The minimal-white frame overo characteristically has a lot of white on itsface and a solid body with minimal white leg markings.

Regardless of the expression of the frame overo pattern, these horses pro-duce overo foals 50 percent of the time. It has been hypothesized that the frameovero is under the control of a single gene, which is designated Fr.

Frame overos are known to produce lethal white foals. It is not known at thistime 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.

Defining Minimal-White Frame Overo• A great deal of white on the face.• Solid bodies.• Normal solid horse,

minimal leg markings.These horses may be registered as Solid Paint-Bred, but in reality they are overos and will produce overos 50 percent of the time.

Splashed White Overo

Breeding the Frame Overo

Frame Overo


The most interesting thing about Paintgenes is that all four seem to be capable ofcombining with each other. The pattern cre-ated through the action of the tobiano geneand any overo gene is referred to as tovero.This name does not indicate which overogene is present—just that the overo andtobiano genes are being expressed in thesame individual.

It is possible that many overo horses havemore than one overo gene creating theircolor pattern. The Medicine Hat Paint hasbeen documented as being produced bycrossing frame overos on tobianos, sabinoson frame overos and sabinos on tobianos.

From a color breeder’s point of view,intriguing statistics are derived from horsescarrying more than one copy of a Paint gene.Ignoring the homozygous tobiano that pro-duces tobiano foals 99.9 percent of the time,a horse carrying two separate Paint genesshould produce a spotted offspring 75 per-cent of the time from solid mates. A horsehaving three independent Paint genes isthought to produce a Paint foal 87.5 percentof the time. For the horse carrying four Paintgenes, the percentage of spotted foals fromsolid partners hits an amazing 94 percent.

So, if the theory is correct and each overopattern is under the control of a separategene, there is more than one way to increasethe odds of producing a spotted foal.

A Paint with one color pattern gene bredto a Paint with two Paint color genes pro-duces a spotted foal 87.5 percent of thetime. If both Paint parents have two Paintcolor-pattern genes, the odds of producinga spotted foal are greater than 99 percent.

The problem is that multiple copies of Paint genes produce more white on horses,and some pairings may create lethal whitefoals.

Breeding the Tovero


Breeding the Sabino Overo

Sabino Overo

Tovero

Defining Minimal-White Sabino Overo

• A great deal of white on the face.• Possible small roaned areas on the body,

often expressed as a narrow white strip upa leg or down the throat.

• Normal solid horse, minimal leg markings.These horses may be registered as Solid

Paint-Bred, but in reality they are overos andwill produce overos 50 percent of the time.

The color pattern referred to as sabinoencompasses a wide range of patterns. Itis possible that more than one pattern hasbeen included in this category, but at themoment we are going to assume that thisis the varied expression of a single gene.This gene has been designated as thedominant Sb gene.

Lethal whites have occurred from themating of two sabinos, but viable whitefoals have also been documented. As withall the overo genes, the wide variation inpattern leads to a lack of predictability.

The sabino pattern is confusing geneti-cally. In many, or most, families, it appearsto be transmitted as a polygenic traitrather than as a single gene. Many horsesappear to transmit it roughly in the per-centage that they are themselves white.That is, a sabino Medicine Hat is likely toproduce a higher percentage of spottedfoals (or at least foals registerable as spot-ted) than is a minimally marked sabino.

Breeding for the sabino pattern has afew interesting quirks. In many breeds it isdesirable to have flashy white marks, butnot body spots. This includes theClydesdale, Shire, Welsh Pony, Arabianand even the Quarter Horse (for somebreeders).

Clydesdale breeders especially like thewhite marks, but most prefer a bay bodycolor. The general rule that manyClydesdale breeders use is to mate horseswith four white feet (and usually roanybodies, resulting from the sabino pattern)to horses with one dark foot. This tendsto result in the mating of horses with toomuch sabino expression to those with toolittle expression. On average, the resulting

foals come out with fairlyminimal expression. In theClydesdale, this meansfew body spots and rel-atively few roans, whichpleases most breeders and buyers of thisbreed. They still do get the occasionalMedicine Hat, though.

Some horses that lack body spots, butthat have the high white socks that creepup toward the body, are indeed sabinosand can be useful in Paint breeding pro-grams. The sabino pattern is a great pre-tender, but is also responsible for somevery attractively marked horses.

The sabino pattern is probably the mostcommon “cropout” from the QuarterHorse and Thoroughbred breeds. In manycases, an investigation of the cropout’sparents reveals horses with extensivewhite markings. In reality, these parentsare probably minimally marked sabinos,which occasionally produce foals withmore sabino expression than themselves.

A few cropouts, including nearly whiteones, have very dark parents, or even par-ents with no white marks. These parentsare clearly not sabinos, and demonstratethat there may be mechanisms that canmask the expression of the sabino pattern.

If the sabino pattern is merely an exten-sion of “normal white marks,” then thismeans that an occasional solid-coloredhorse (with no white marks) may be ableto mask both white marks and the sabinopattern. The practical consequence of thisis that such horses make poor choices foran outcross breeding program becausethey can decrease the percentage of spot-ted foals.



A good horse is a good horse, regardlessof its color. Yet, color can be a major assetwhen a horse is for sale, and it can make adifference in the amount of attention a horsegets in the show ring.

In addition to sporting various patternsof white patches—expressed as tobiano,frame overo, sabino, splashed white ortovero—every Paint Horse also has a back-ground color.

Coat patterns have many background col-ors, and controlling them genetically can becomplicated. Anyone wishing to breed forspecific background colors has an interest-ing challenge before them. The breedermust combine specific colors with specificPaint spotting patterns, which requires care-ful planning and a knowledge of genetics.

Some Paint breeders prefer darker back-ground colors, such as bay, chestnut andblack, over the lighter colors such as dun,palomino, grullo or buckskin. The reasonfor this preference is because the contrastbetween the white Paint patterns and thedarker base colors shows up better than itdoes with the lighter colors.

This rule, though, is not absolute, and thelight-colored duns, grullos, buckskins andpalominos are popular among many breed-ers. Taste in color is an individual preference.

Perhaps it is because of this variety ofpreferences that coat color genetics is one ofthe few areas of equine genetics where sci-entists have been able to develop sophisti-cated theories about how specific genesdetermine the color of a horse’s hair.

However, it is important to realize thatmuch of the theory of coat color genetics isjust that—theory. At this point in time, onlythe presence of four color genes can be con-firmed in the laboratory: the tobiano gene,the recessive form of a gene that creates ared horse, the cream gene and the agouti(bay/black).

The action of the rest of the color genes ispurely hypothetical. Because of this, theo-ries may change as more tests become avail-able to identify specific genes.

Identifying coat colors can also be confus-ing. There is a tremendous range of shadeswithin a color, and different types of colorwithout recognized names. There are alsocoat colors that appear to be identical but areunder the influence of different genes.

Breed associations have also contributedto some of the confusion. Thoroughbredsregistered by the Jockey Club are calledroans if they have a red body with whitehairs. According to their definitions, graysare dark horses that are graying. Technically,

whenever the gray gene is present, the horseis gray regardless of basic coat color. Horsesof any color (with the exception of truewhite) can gray.

The American Quarter Horse Association,trying to keep up with the current coat colortheory, has changed the description of a“buckskin.” In the past, a buckskin was anycanvas-colored horse with black points. Itcould have zebra markings and a line-backand still be a buckskin. Today, all line-backed horses with zebra markings arereferred to as duns by AQHA, unless theyare sorrel or chestnut duns. These are calledred duns. Black duns are called grullos.

APHA’s color criteria is the most descrip-tive of the three associations when it comesto roan, giving roan three basic colors: black(blue), bay and red. Starting in 2000, itbecame possible to register bay roans, whilethe term red roan designates sorrel/chestnutroans.

If all of this sounds confusing, take heart.It is possible to stack the deck in your favorwhen trying to produce a specific-coloredoffspring—if you understand the underly-ing genes that create the colors.

Coat Colors



The Basic Rules of Coat Color Genetics

While it is true that the control of color is complicat-ed, it is also true that the lighter colors are all dominantto the darker ones. This general rule is oversimplified,but it works in most cases.

Therefore, the light colors do not pop out—exceptrarely—as surprises. That is, you have to breed to alight color to get a foal of a light color. This fact hassome consequences for Paint breeders.

If the breeder prefers the darker base colors, then itis important to always select the darker colors for theirbreeding programs. This is especially true if outcross-es are sought, because the lighter colors are fairly com-mon in the Quarter Horse. They are present, but rare,in the Thoroughbred.

On the other hand, if the light base colors are desired,then it is important for the breeder to always include atleast one light-colored parent in matings in order toboost the chances of producing a light-colored foal.

The downside of using two light-colored horses in across (specifically palominos and buckskins) is theoccasional production of cream-colored horses—thecremello and perlino. These horses are nearly white,and it is difficult to see the contrast between any Paintspotting and the pale background color.

The line-backed dun colors only rarely can producea cremello foal, making them safer to mate to otherlight colors because cream foals occur in such mat-ings infrequently.

The darker colors, usually considered to include bay,chestnut and black, are easier for most breeding pro-grams. These have a peculiar interaction in that chest-nut (and sorrel) are recessive to bay and black, but actto cover them up. This means that it is impossible to telljust from looking whether a chestnut or sorrel horse hasthe genetic makeup to produce black or bay. Testing forthe Agouti gene is helpful.

Reviewing the rulesTo review, the basic rules for producing colors are:

• It usually takes at least one light-colored parent toproduce a light-colored foal.

• Chestnut and sorrel, when mated to one another, canproduce only more chestnuts and sorrels.

• Bay mated to bay, black or chestnut/sorrel can pro-duce bay, chestnut, sorrel, and, rarely, black.

• Black mated to black produces black (or, rarely,chestnut or sorrel).

• Black mated to bay will usually produce a bay, fairlycommonly produces chestnut or sorrel, and onlyrarely produces black.

• Black mated to chestnut will usually produce bay, butalso chestnut or sorrel, and, rarely, black.Color prediction is never 100 percent accurate. The

best way to maximize the chance of a specific darkcolor is to test for the Agouti gene or to mate two par-ents of that color. Any other approach drasticallydecreases the probability of achieving the desired colorin the foal.

Bay HorsesBay is the second most common horse color. Controlled by the A gene, a

bay horse has a reddish brown body with black points. The A gene createsthese black points by limiting the placement of black on the horse’s coat tothe mane, tail, legs and ears.

The two genetic loci (locations) that control the color of the bay, blackand sorrel horse are the Agouti (A) and Extension (E). The way these lociinteract creates these threebasic body colors.

Agouti controls the distri-bution of the red and blackareas on horses that can formblack pigment, i.e., blacks,bays, buckskins, etc.

The dominant A generestricts black to the points,creating a bay. The recessive Agouti gene (a) does not restrict the black, result-ing in an all-black horse. Therefore, foals with the genotype AA or Aa will bebay and those with the aa genotype will be black, providing they have thedominant Extension gene.

The Extension locus interacts with the Agouti to restrict or allow theexpression of black, but unlike the bay gene, it is the recessive form of theExtension loci that does not allow the color. As a result, a foal inheriting twocopies of the recessive black gene (ee) will be completely sorrel or chestnut,regardless of what type of Agouti alleles it carries.

In his book Equine Color Genetics, Dr. Philip Sponenberg describes theAgouti and Extension loci as switches. As a way to remember the effect eachgene has on a horse’s color, one can imagine that the Extension locus deter-mines if the horse is “chestnut” or “not chestnut.” If the horse is “not chest-nut,” then the Agouti locus acts as a switch to determine if the horse is “bay”or “black.”

Understanding how the A and E genes work to create the bay color and affectthe occurrence of sorrel and black will help you to better determine how othercoat colors are created. However, there are still many subtle shades of the baycoat that cannot fully be explained by the action of the A and E genes.

Bays range in color from dark mahogany bays to blood bays to goldenbays. These bay shades are thought to be under complex, multifactor genet-ic control. Even environment and nurture can cause a variation in coat color,with well-fed horses having a deeper, richer coat than those lacking in nutri-tion. Again, Sponenberg says these variations can be viewed as switches thattrigger either a “dark,” “middle” or “light” shade.

Regardless of the many color variations, bay foals are all born with blacktips on their ears. In addition, most of have black manes and tails; however, their legs may be light at birth and later shed to black.

Heterozygous Bay (AaEE) Mated to Chestnut (Aaee)

BayAE aE

AeAAeE AaeEbay bay

ae aAeE aaeEbay black

Chestnut

Bay



Black and Brown HorsesThe black coat color is controlled by the E gene. It is the

expression of the dominant E gene. The homozygous blackhorse (EE) has a very rich, black coat that is sometimes calledjet black or coal black. Black horses have an entirely black coatand 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 orreddish hairs on the muzzle or flanks.

Black is a popular color with many breeders, but it isfairly rare. The most reliable way to produce black horsesis by mating two homozygous black horses. Breedingtwo heterozygous blacks is the second choice andbreeding a black to any other color horse that carries ablack gene is third. The reason for this is that the E geneis dominant over the e and the CCcr genes that are pres-ent in palominos. Fortunately, breeders can have theirblack or brown horse tested for the recessive e gene sothat they can determine if it is homozygous (EE) or het-erozygous (Ee).

The problem with breeding black to sorrel is that manyred horses carry the A gene, which turns the black coat to bay.According to statistics, a heterozygous black and a chestnutshould produce a black foal 50 percent of the time.

However, this is valid only if the chestnut horse (ee) does notcarry the A gene. If the chestnut parent is heterozygous for thisA gene, 50 percent of the blacks will become bays. If it ishomozygous for this gene, 100 percent of the foals will be bay.

Black foals are usually born with a blue-gray hue to their coatand will typically shed to black as weanlings or yearlings.

Mating Two Heterozygous Black Parents (Ee)

BlackE e

E EE Eeblack black

e eE eeblack sorrel

Black

Brown

Black

Chestnut

Sorrel

Chestnut and Sorrel HorsesThe chestnut horse and the sorrel horse are homozygous reces-

sive ee individuals. Though there is no distinction between the twocolors in the Jockey Club, most breed associations consider thechestnut and sorreldifferent.

Both have a red-dish body color witha reddish mane andtail, which can varyfrom dark to light toflaxen. The differ-

ence is in thedepth of the body color. Chestnuts are a darker red that issometimes close to black. Sorrels are a lighter or bright red.

For the purpose of learning to utilize color genetics, thisguide 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 palominocolor, to black chestnut. The best way to distinguish a blackchestnut from a black or brown horse is by the copper-coloredhighlights on its legs.Regardless of shade, two chestnut parents will always pro-

duce a chestnut foal, making it the easiest color to breed for. Matingof two heterozygous blacks (Ee) will produce chestnuts 25 percentof the time.

In addition, sorrel is a valuable color when trying to breed col-ors based upon the red color, like palomino, red roan and red dun.

Sorrels that have two copies of the recessive Agouti locus (aa) arevaluable to breeders raising black horses because they will not turnblack to bay. For the same reason, it will never produce a bay roanwhen bred to a blue roan. A test is available to determine the genet-ic A code of sorrel individuals.

Sorrel and chestnut foals are born with reddish coats that maylighten or darken when they shed.

Mating Heterozygous Black (Ee) Mated to Sorrel (ee)

BlackE e

e eE eeblack sorrel

e eE eeblack sorrel

Sorrel


Cremello and Perlino HorsesA horse that receives two copies (CcrCcr) of the cremello gene

has a cream-colored coat with pink skin and blue eyes. Whentwo pairs of Ccr occur in a horse with a chestnut base color, theresulting body coat color is called cremello. When two Ccr genesoccur in a horse with a bay base color, it creates a color knownas perlino.

As foals, a perlino and cremello look almost identical, bothwith pink skin, blue eyes and a washed-out coat color. Whitemarkings on the face and legs are barely visible next to the slight-ly yellow coat. Sometimes, these foals are mistakenly referred toas albinos.

Many breeders will not mate two palominos because of thechance of raising a cremello. Using the Punnett Square, you candetermine that 25 percent of the foals from a palomino-to-palomino mating will receive two copies of the CCcr gene.

Breeding palominos to buckskins, or buckskins to buckskins,results in a 25 percent chance of raising a perlino. The cremellogene creates both the buckskin and the palomino—the only dif-ference is the base color upon which it is acting. Both palominosand buckskins result from the heterozygous (CcrC) cremello genecombination. However, the buckskin’s base coat color is bay, andthe palomino’s base coat color is sorrel or chestnut.

The benefit derived from cremello and perlino breeding stockis that Paint breeders can produce palominos and buckskins 100percent of the time. A cremello bred to a sorrel will always pro-duce a palomino and a perlino bred to a bay or sorrel will alwaysproduce either a palomino or buckskin.


Champagne and Cremello GenesScientists have identified three genes that create the

coat colors palomino, buckskin and dun. Of these genes,the champagne and the dun (see page 13) gene, expressthemselves according to the rules of similar dominance.As a result, they dilute the horse’s base color only whenthe dominant expression of the gene is present. Whetherthe horse has two copies of the dominant gene or onlyone, the coat color looks the same.

Palomino/Buckskin (CcrC) Mated to Palomino/Buckskin (CcrC)

Palomino/Buckskin

Ccr C

Ccr CcrCcr CcrChomozygous dilution

dilution (cremello/perlino)

C CCcr CCdilution no dilution

Palomino/Buckskin

The Champagne GeneThe champagne (Ch) gene is not as commonly recognized

as some other genes for coat colors. The dominant form ofthe champagne gene (ChC) gives horses an iridescent glowto their coats. Their eyes are amber and their skin is pump-kin-colored or a pinkish-gray. Researchers have identifiedthe gene in the Tennessee Walking Horse, the RockyMountain Horse, the Quarter Horse and the Paint Horse.

In his book Equine Color Genetics, Sponenberg reportsthat the champagne gene dilutes a chestnut coat togolden with a flaxen mane and tail (golden cham-pagne). Its action on black turns the coat to classicchampagne, the bay coat becomes tan with a dilutemane and tail, known as amber champagne, while theaction on brown becomes sable champagne.

A champagne-dilute foal is often born dark-colored andwill lighten to champagne when it sheds for the first time.For this reason, it is likely that many champagne horseshave been registered as palomino, buckskin and sorrel.

Owners of champagne horses who want their horse’scolor recognized can contact the International Cham-pagne Horse Registry, which is the official registry forthe color. To find out more, log on to their Web site atichregistry.com.

The Cremello GeneThe cremello gene produces the palomino and buckskin

color, but unlike the other dilution genes, it follows the ruleof incomplete dominance. As a result, the gene canexpress itself in three ways, depending on the combina-tion in which it occurs.

One copy of the dominant (Ccr) gene turns the horse’scoat 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 ruleapplies to the champagne and dun genes.

Perlino

Cremello



The palomino horse is a chestnuthorse (ee) with one Ccr gene. ThePalomino Horse Breeders of America, acolor breed registry for palominos,describes the color as that of a U.S. 14karat gold coin, with variations from lightto dark. However, the body coats canvary from a smoky gray to creamy yel-low. Palominos may have manes thecolor of their bodies or they can bewhite, silver or mixed with sorrel. Theirskin is usually gray, black, brown or mot-tled, without underlying pink skin orspots except on the face or legs.

A palomino foal’s true color may notbe evident at birth. Some will have yel-lowish bodies and white manes andtails, making them easy to identify. Butsome are born with a sorrel coloring.These foals tend to have an orange orpink tint to their coats, and their manesand tails may be slightly red. As wean-lings or yearlings, these foals will shedtheir sorrel coat for their true palominocolor.

Fortunately, a breeder in doubt hasone sign on which they can rely. Thecolor of the foal’s eyelashes provides agood clue to the foal’s eventual coatcolor. Palominos born with sorrel coatsusually have light, golden eyelashes.

For breeders who cannot utilizecremellos or perlinos in their breedingprograms, crossing a sorrel with apalomino has the best odds of produc-ing a palomino—a 50 percent chance.

A palomino mated with a black horsemay produce a palomino or a black foal,depending on which black gene combi-nation it receives. The black gene (E)masks the expression of the Ccr gene.This is why a black horse crossed on apalomino is the third-best way to pro-duce a black foal. Also, a heterozygousblack (Ee) horse with a palomino parentcan produce a palomino if it passes on arecessive e and a Ccr. If that horse’smate also has the recessive e gene, the

resulting foal can receive an eeCcrCcombination, making it a palomino.

A variety of coat colors can resultwhen breeding a palomino to a het-erozygous bay. These foals have a 25percent chance of becoming buckskin,palomino, bay or sorrel.

Of course, the Punnett Square only esti-mates gene action, because there areother factors that change breeding per-centages. Its predictions work over a largepopulation, but any horse can deviate.

Palomino Horses

Palomino (eeaaCcrC) Mated toHeterzygous Bay (EeAaCC)

PalominoeaCcr eaC

EAC EeAaCCcr EeAaCCbuckskin bay

eaC eeaaCCcr eeaaCCpalomino sorrel

Bay

Buckskin HorsesBuckskins are canvas-colored with black tips

on their ears and black legs, like bays. Their bodycolor ranges from purple to sand to cream.

Buckskin is produced by the dominant cremel-lo gene (Ccr) acting on a bay base color.

Buckskin foals are fairly easy to identifyat birth. Born with light bodies and blackear tips, their legs may be dark but usu-ally appear light and then shed to dark.

Markings can be tricky to detect on a buckskin Paintwhen the Paint gene colors the legs white. Hoof colorcan sometimes be helpful, as a buckskin Paint shouldhave dark hooves.

For breeders who cannot utilize cremellos or perli-nos in their breeding programs, crossing a bay with abuckskin is the second-best way of producing the

color, with a 50 percent chance.A 50 percent chance can

also be obtained by breeding a palomino to a bay that is homozygous for the blackgene and the bay gene (EEAA).This cross also produces 50percent bays.

Palomino (eeaaCcrC) Mated to Homozygous Bay (EEAACC)

PalominoeaCcr eaC



Bay


The coat color categorized as dun has oneof the broadest ranges of colors and mark-ings. For APHA purposes, horses with a duncoat are categorized as either dun or red dun.

Dun is the result of the dominant dungene (Dn+) working on a bay base coat. Theeffect is to lighten the body to a tan or gold-en yellow color. A red dun occurs when theDn+ gene expresses itself on a chestnut orsorrel coat. Red duns have a light red,orangish or sometimes apricot coat color.

All duns, regardless of body color, have onething in common—primitive markings. Thereare basically four types of primitive markings:zebra stripes, dorsal stripe (lineback), withersstripe and cobwebbing. Zebra stripes are barson the side of the hocks and above or belowthe knees. A dorsal stripe is a dark stripe downthe back. A withers stripe is a stripe across thewithers, 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 combina-tion of these markings.

Researchers believe the dun gene lightensthe body, leaving the horse’s dark points unaf-fected and leaving the head darker than thebody. The mane and tail are also often darker.

The lineback is the most common dunfeature. The darker color of the lineback

often continues into the maneand tail, where the gene actiondarkens the center of the hairand leaves the edges lighter.

Dark-colored horses such asblack, bay and chestnut may havea back stripe without a lightenedbody color. Similarly, foals aresometimes born with a linebackthat disappears when they shed. However,scientists believe these back stripes are notcaused by the dun gene. These back stripesare referred to as “counter-shading”.

Dark edging on the ear is another com-mon dun characteristic, but because thischaracteristic is common in other colors, it is

probably not related to the dun gene (Dn+).Following the rules of similar dominance,

the recessive dun gene (Dnnd) does not affectthe outcome of a horse’s color. Scientists stilldo not know if the dun gene acts alone, or ifthere are other genes that work to create themany different dun characteristics.

Dun Horses


Heterozygous Dun (eeaaCCDn+Dnnd) Mated to Homozygous Bay (EEAACCDnndDnnd)

DuneaCDn+ eaCDnnd

EACDnnd EeAaCCDnndDn+ EeAaCCDnndDnnd

dun bay

EACDnnd EeAaCCDnndDn+ EeAaCCDnndDnnd

dun bay

Bay

Primitive Markings

Leg Barring: Horizontal stripes of varying widths appearingacross the hocks, gaskins,forearms or knees.

Dorsal Stripe: Darker band of color run-ning along the backbonefrom the withers to/into thebase of the tail.

Shoulder/Traverse Stripes: Neck and shoulder shadowing appearing asdark areas through theneck or withers.

Grullo HorsesGrullo is one of the rarest expressions of

the dun gene because it results from theaction of the dun gene on a black basecoat. It was once believed that grullosresulted from crossing palominos with blackhorses, but genetic research has sinceproved that theory incorrect.

The grullo coat varies from beige to bluish-gray to slate blue. They usually have dark orblack heads and black points, mane and tail.

As the dun gene acts through similardominance (see page 14), grullo is createdby a single copy of the Dn+ gene. However,homozygous duns (Dn+Dn+) do exist andwill pass on a dominant dun gene to eachof their offspring, resulting in 100 percentduns and grullos.

Another interesting resultof the dun gene occurswhen a horse also carriesthe dominant form of thecremello (Ccr) gene, whichcreates cremellos, perlinos,palominos and buckskins.A black horse that receivesthe Dn+ gene and is also heterozygous for the

cremello gene (CCcr) will result in a palergrullo. On a bay base coat, the primitivemarks may remain but the body becomesmore yellow, like a buckskin. On a sorrelcoat, the primitive marks may be lost alto-gether and the body becomes the color ofa palomino. For this reason, the colors ofsome horses mayhave been incorrect-ly registered, whichcould explain whybreeders oncebelieved a palominocould produce a grullo. In actuality, thepalomino was ap a l o m i n o -colored dun without the dorsal stripe.

Scientists believe that when CCcr x Dn+occurs, the gene that has the most extremeexpression of the base coat color is the onethat is dominantly expressed. For instance,a chestnut coat would be lightened topalomino because palomino is a moreextreme change than is red dun.

Heterozygous Black (EeaaCCDnndDnnd) Matedto Heterozygous Red Dun (eeaaCCDn+Dnnd)

BlackEaCDnnd eaCDnnd

eaCDn+ eEaaCCDn+Dnnd eeaaCCDn+Dnnd

grullo red dun

eaCDnnd eEaaCCDnndDnnd eeaaCCDnndDnnd

black sorrel

RedDun



The Difference Between Roan,Gray and White

Three of the most easily confusedcolors are roan, gray and white.Though all result from white beingadded to the horse’s base coat, eachhas a unique way in which it occurs.

The roan gene (RnRn) covers specificparts of the body with a light coating ofwhite hairs that are evenly mixed withinthe base coat. The gray gene (G) beginsas a light sprinkle of white over the entirecoat. Each year, more white hairs areadded to the coat until it is completelygray or white. The white gene (W) com-pletely covers the body with an even,white coat before the foal is born.

By becoming familiar with the spe-cific characteristics unique to eachcolor, a breeder can reliably identifyone from the other. Because thesethree genes add white to the basic coatcolor of the horse, the horse’s othergene combinations of E, A, Ccr, Dnnd,Ch, etc., still determine the color that isbeing covered by the coating of white.

Roans are often confused with gray horsesbecause both are characterized by havingwhite in their hair coats. However, the differ-ence between the action of the roan gene andthe gray gene is evident once you understandthe specific effect each has on a horse’s coat.

The action of the RnRn gene places a certainamount of white hairs in the body coat.Sometimes, the roan pattern is uneven and isdisplayed in a paler fashion on areas such asthe hindquarters, the heart girth, the barrel andthe dock of the tail. Unlike the gray horse, aroan’s head, mane, tail and lower legs usuallyremain solid or darker than the rest of its body.

A roan foal’s color may be evident at birth, ormay reveal itself after it sheds its foal coat. Aroan horse does not grow more white hair as itages. Instead, a roan coat may appear lighterin the spring and darker in the winter months.

The roan gene is dominant. It is believedto be linked to other genes that determine thehorse’s color, which complicates determiningthe inheritance of the gene because theselinked genes are usually passed along as aunit. The roan gene is closely associated withthe E gene, which determines a red or blackbase color, and the TO (tobiano) gene. Thus,roans have a higher percentage of offspringthat are the same color as the roan parent.

For example, red roans, which have a sor-rel base coat, bred to sorrels, produce 50percent sorrels and 50 percent red roans. Ablue roan, whose roan gene is linked to its

dominant E (black) gene, is apt to producea high percentage of black and bay roans. Ifa horse’s roan gene is linked to the recessivee (sorrel) gene of a heterozygous (Ee) indi-vidual, the horse should produce only redroans when bred to sorrel mates.

Homozygous roans are extremely rare.Though it was once believed that theRnRnRnRn combination was lethal, the exis-tence of a few homozygous roans disprovesthis theory.

It is important to keep in mind that thegenetic codes controlling the roan gene areextremely complicated, so this is only a basicdiscussion of the coat color. Without a doubt,there is an exception to every rule and a hid-den factor that cannot be seen on the surface.

Blue RoanBlue roan is the common term for the

RnRn gene acting on black. White hairs aredispersed over the body, giving a blueappearance to the horse. The head, legs,mane and tail are very dark.

Red RoanThe base coat of a red roan is sorrel or

chestnut. Red roans have a uniform mixtureof white with red hair on a large portion ofthe body, but are usually darker on the headand lower legs. The mane and tail may bered, flaxen or white.

Red roans with white legs and a blaze faceare often referred to as strawberry roan, aterm APHA does not officially recognize.

Horses with strawberry roan markingshave shown a tendency toward producingexcessive white by Quarter Horse standards.It may be possible to influence the occur-rence of excessive white by carefully screen-ing the mates for strawberry roans. Chestnuthorses with stockings and blazes increase thechance that the white markings will spread.Solid-legged and solid-faced mates may helpto keep the color to a minimum.

Researchers have also discussed the possi-bility that some of the strawberry roanmarkings are an expression of the sabinoovero pattern gene.

Bay RoanThe bay roan, which has a bay base coat,

is often called a red roan. APHA distinguish-es between roans with bay base coats andthose with sorrel or chestnut. The categoryof bay roan was added to the registrationform, separating the two basic coat colors.Only sorrels and chestnuts with the roangene are now registered as red roans.

Blue Roan (EeRn+RnRn) Mated to Sorrel (eeRn+Rn+)

Blue RoanE Rn+ eRnRn

eRn+ eERn+Rn+ eeRn+RnRn

black red roan

eRn+ eERn+Rn+ eeRn+RnRn

black red roan

Sorrel

Roan

Blue Roan

Red Roan

Bay Roan


In most breeds, including Paint Horses,true white horses are rare. Keeping this inmind, it may seem unusual to learn that thewhite gene (W) is dominant over all othercoat colors, including gray. This means thatany foal receiving one dominant white genewill be white.

White foals are born white and have darkeyes and pink skin, which eventually distin-guish them from a gray horse. If they have aPaint Horse coat pattern, it is not identifiablebecause the markings blend in with their haircoat, unlike perlinos and cremellos, whichhave visible patterns and blue eyes.

APHA has included the white color on its registration form for some time. ApHC and the Jockey Club also list white as a registerable color, but it is extremely rare inboth breeds.

Even though the white gene is known tobe dominant, it is still somewhat of a mys-tery to scientists because two dark-coloredparents have been known to produce awhite foal. To explain this, researchers haveconcluded that a dark-colored parent carry-ing the recessive white gene (w) can pass acopy of this gene to their offspring. Onceinherited by the unborn foal, the recessive

white gene may mutate to the dominantform, creating a white foal. The white foalsthat resulted from these matings went on tobreed as if they carried the W gene. Thismay suggest that the white allele has a highspontaneous mutation rate.

According to the Punnett Square, a whitehorse mated with a dark-colored horse willproduce a white foal 50 percent of the time.Mating two white horses results in 50 per-cent white foals and 25 percent dark foals.(Before a white horse produces offspring, it

is impossible to know what color of darkfoals it will produce unless you have exten-sive knowledge of the horse’s color pedi-gree.) The other 25 percent of the foalsproduced from a white-to-white mating arelethal. These homozygous white foals (WW)are usually resorbed during gestation.

However, these homozygous white foalsare not genetically like foals that have OveroLethal White Syndrome, which results froman overo-to-overo mating.

White Horses


Gray HorsesWith horse people and non-horse people

alike, gray is one of the most popular coatcolors. Perhaps this is because it seems tohide conformational faults and can make aplain head appear beautiful.

The irony is that gray is often an undesir-able gene for breeders of white-patternedhorses because the contrasting darker colorgradually fades away. Because the gray (G)gene is dominant over all the genes dis-cussed so far, it will eventually turn all othercoat colors—dun, roan, bay, black, buck-skin, champagne, dun, palomino, roan andsorrel—white.

However, the gray gene does not affectthe white hair on the horse’s body that is created by Paint Horse pattern genes,such as tobiano or overo, or white thatoccurs as a blaze, stocking or other mark-ing. These white markings remain visibleeven as the gray horse becomes whiter-looking with age.

Because gray horses do become whiterwith age, they are sometimes confused withthe white horse. The difference is that amature gray horse may appear white, buthas dark eyes and dark skin. A white horsealso has dark eyes but has pink skin.

Gray horses areborn with a col-ored coat suchas black, bay,sorrel, dun,etc. Their foalcoat typically reflects the base coatcolor, which the gray gene eventuallyturns white. A gray foal can sometimesbe determined by white rings in their hair coats and around their eyes. This is often thebeginning of the graying process, whichvaries from horse to horse. The grayingprocess may occur over several years or alifetime. The tail of a gray horse may alsobecome whiter or remain dark.

In addition to its variable process, the graygene creates many shades and patterns,including primitive markings, dapples (round,shaded spots) and “fleabitten” coats (flecksof color dispersed throughout the body). It isstill unknown which genes control the shadesand patterns of grays and the speed of thegraying process. Therefore, the idea that ahomozygous gray (GG) will turn white fasterthan a heterozygous gray (Gg) is unproven.

What is known is that homozygous graysdo exist and they produce gray offspring 100

percent of the time. Heterozygous graysproduce gray foals 50 percent of the time.

Unfortunately, both homozygous and het-erozygous grays are prone to melanomas(skin tumors). These tumors commonlyoccur beneath a gray horse’s tail and aroundits ears. Fortunately, though they can beunsightly and disfiguring, only about 5 per-cent of these melanomas are malignant.

Distinguishing Differenced Between White and Cremello/Perlino Horses

White (W) Cremello/Perlino (CRCR)birth color white cream to white

eye color dark blue

skin color pink pink

visibility of not visiblewhite markings visible

genetic base coat any genetic sorrel or chestnut for cremello,combination bay for perlino

color production produces 50% white horses produces 100% palomino or potential regardless of mate’s color buckskins, depending

on genotype of mate



A Lethal White is a foal of overo lineage, born all white or mostlywhite. The foal may seem normal at birth, but usually begins show-ing signs of colic within 12 hours because of a non-functioningcolon. Because the syndrome is always fatal, lethal white foals areoften euthanized.

This condition, referred to as Overo Lethal White Syndrome(OLWS), is always fatal, and results in both emotional and economicloss to breeders.

Occurrence of Lethal White SyndromeThe body of all living things is made of protein, minerals and water.

The proteins comprise a large proportion of the body’s structure, andalso regulate body functions by acting as hormones and enzymes.

The building blocks of proteins are amino acids, and the function ofthe protein is dependent on the order of the amino acids. The order ofthe amino acids is determined by DNA, which codes for the compo-sition of the body, its growth and function.

The code for inherited conditions such as OLWS is in the DNA, andtherefore its composition must be determined before it can be knownhow it causes disease.

Similar to how a protein is made of amino acids, DNA is made ofbases. These bases are arranged in triplets that code for the aminoacids.

When the base pairs change (through mutation) and cause an aminoacid substitution, the function of the protein coded is altered. Thealteration of protein function causes genetic traits, including disease.

Causative genes are responsible for similar conditions in otherspecies, so research to determine the order, or sequence, of base pairsand the resulting amino acids for two “candidate genes” is crucial tounderstanding OLWS.

Finding the Lethal AlleleBased on studies by the University of Minnesota’s Equine Genetics

Group and Portland University, it has been concluded that OLWS foalshave two lethal alleles (L/L); their parents have one normal and onelethal allele (N/L), and solid-colored horses of other breeds have twocopies of the normal allele (N/N).

This is strong evidence that the gene mutation detected is responsi-ble for OLWS. To date, researchers have tested almost 1,000 horses,and the results are consistent.

Proving the Lethal TheoryIt appears that all overo horses are not the same, at least for this

gene. Overos can carry either (N/N) or (N/L). Researchers have notfound a living adult horse that has two copies of the lethal sequence(L/L), and they have tested several all-white Paints.

The geneticists have found carrier horses in overos, tobianos,toveros, Solids, crop-out Quarter Horses and Pintos. The discovery ofthe Lethal allele in Pintos is important in limiting the spread of thismutation, because many Pinto breeders are unfamiliar with OLWS andthe gene is now making its way into other breeds that are crossing ontoPintos for color production.

By taking the lead in the investigation of OLWS, APHA has providedvaluable information to all breeders.

Genetics in Overo Lethal White SyndromeIn the past few years, Lethal White Syndrome has been heavily exam-

ined from a genetic standpoint. In 1997, APHA approved a grant to the

Lethal Whites—Fact Versus FictionAccording to researchers at the University of Minnesota,

there are three issues that may account for the fact that wedo not see 25 percent of all overo-to-overo crosses pro-ducing lethal whites:1. Not all lethal white foals survive to birth. Some are

resorbed or aborted by the mare.2. Not all lethal white foals that are born are reported.3. Not all patterns that are currently classified as overo,

such as sabino or splashed white, are lethal whenhomozygous.

In addition, many myths cloud the truth regarding lethalwhite syndrome. Below, the University of Minnesota EquineGenetics Group dispels nine of the most common myths.

1. Myth: All overo horses are carriers of the lethal allele.Fact: There are many overos that do not carry the lethal allele.

2. Myth: Twenty-five percent of foals from two overo parents will be lethal whites.Fact: Because there are overos that do not carry theallele, the incidence of lethal white syndrome is lessthan 25 percent in overo-to-overo matings.

3. Myth: Registered tobianos, Solids or Paint crossescannot carry the lethal allele.Fact: There are tobianos that have overo bloodlines,and these horses can be carriers of the lethal allele.Solids and Paint crosses can carry the lethal allele.

4. Myth: Totally white Paints are not carriers of the lethal allele.Fact: These white horses are often carriers of the lethal allele.

5. Myth: All totally white foals born to two overo parentsare lethal whites.Fact: There are totally white Paints that are not affect-ed by the lethal white syndrome.

6. Myth: Mares cannot produce lethal foals in consecutive years.Fact: The genetic makeup of one foal does not affectsubsequent births.

7. Myth: Only one parent determines if a foal will be alethal white.Fact: Both the sire and the dam contribute a copy ofthe lethal allele.

8. Myth: Crop-out Quarter Horses cannot carry the lethal allele.Fact: A small number of crop-outs have been testedand found to be carriers of the lethal allele.

9. Myth: You can reliably tell the carrier status of a Paintby their color pattern.Fact: This is false.

Overo Lethal White Syndrome



ReferencesBowling, Dr. Ann T., Veterinary Genetics Laboratory, University of

California-Davis School of Veterinary Medicine. Interview by KimGuenther.

Bowling, Dr. Ann T., “Dominant Inheritance of Overo Spotting in PaintHorses,” The Journal of Heredity Volume 85, No. 3 (May/June 1994).

Duffield, Dr. Debbie, and Dr. Peg Goldie, Spotted Horse ResearchGroup of Portland State University, Oregon. Interview by KimGuenther.

Evans, J. Warren, Anthony Borton, Harold Hintz, and L. Dale VanVleck. The Horse. Second edition. New York: W. H. Freeman andCompany.

Fio, Lauri, “The New Genetics of Overo,” The Horse Report Volume 12,No. 2 (October 1994).

Guenther, Kim, “Predicting Color,” Parts 1-3, Paint Horse JournalVolume 29, No. 1 (January 1995): 48-54; No. 2 (February 1995):48-54; No. 3 (March 1995); 82-87.

Holmes, Frank, “A Lighter Shade of Red,” Paint Horse Journal Volume32, No. 12 (December 1998): 72-80.

Holmes, Frank, “The Mystery of Tovero,” Paint Horse Journal Volume31, No. 12 (December 1997): 130-139.

McCall, Dr. Jim and Lynda, “The ABCs of Coat Color Genetics,” Parts 1-4, Paint Horse Journal Volume 33, No. 12 (December 1999): 82-85;Volume 34, No. 1 (January 2000): 92-95; Volume 34, No. 3(February 2000): 76-79; Volume 34, No. 4 (March 2000): 78-83.

Ramsbottom, Ann, “Understanding Tobiano Genetic Markers,” PaintHorse Journal Volume 24, No. 1 (January 1990): 54-55.

Sponenberg, Dr. D. Philip, “A Sabino Case in Point,” Paint Horse JournalVolume 32, No. 12 (December 1998): 81-83.

Sponenberg, Dr. D. Philip, “The Genetic Equation,” Parts 1-8, PaintHorse Journal Volume 28, No. 1 (January 1994): 12; No. 2 (February1994): 12; No. 3 (March 1994): 12; No. 4 (April 1994): 12; No. 5(May 1994): 12; No. 6 (June 1994): 12; No. 7 (July 1994): 12; No. 8(August 1994): 12, 50.

Sponenberg, Dr. D. Phillip, and Bonnie V. Beaver. Horse Color. CollegeStation: Texas A&M University Press, 1983.

Vrotsos, Paul D. R.V.T., and Elizabeth M. Santschi D.V.M., “Stalking theLethal White Syndrome,” Paint Horse Journal Volume 32, No. 7 (July1998): 500-502.

Walker, Dawn, “Lethal Whites: A Light at the End of the Tunnel,” PaintHorse Journal Volume 31, No. 2 (February 1997): 114-119.

If you would like to learn more about equine color genetics,some suggested readings are:Equine Color Genetics by Dr. D. Phillip Sponenberg. Published by Iowa

State University Press in 1996. To order a copy, call (800) 862-6657.Horse Genetics by Dr. Ann T. Bowling. Published by Oxford University

Press in 1996. To order a copy, call (800) 445-9714.

University of Minnesota to support a researchstudy aimed at locating the gene responsiblefor OLWS and developing a test to determinethe disease.

Led by Dr. James Mickelson, Dr. StephanieValberg and Dr. Elizabeth Santschi, theresearch has now identified the gene that isassociated with OLWS and is likely responsi-ble for the condition.

Researchers are still working to more com-pletely describe the inheritance of overo and,more than ever, it is clear that overo horsesare at risk of carrying the OLWS gene.

Fortunately, horse breeders can now testtheir stock for the presence of this gene anduse this information to assist in making mat-ing decisions. This test allows breeders topositively identify horses that are carriers ofthe gene and to find new pedigree sourcesfor their color breeding programs.

Testing for Lethal WhiteThe diagnostic test for the overo gene

uses a process known as ASPCR (allele spe-cific Polymerase Chain Reaction). The testcan be performed from either blood or hairsamples with roots (hair preferred). The testidentifies a specific mutation site in theDNA sequence that has been shown to beassociated with Lethal White overo foals.Researchers know of no other mutationsthat are associated with Lethal White overohorses. However, owners requesting thediagnostic test should be certain to under-stand that there is the rare possibility thattwo NN horses could have a Lethal Whitefoal, due to the sire and dam having in com-mon a mutation at a site other than the onedetected by this test.

Performing the TestThe test for the lethal form of the gene

associated with OLWS is available from twouniversities.

All tests require hair samples be pulledfrom the mane or tail with the roots intact.The number of hairs required ranges from15-30. Hair samples can be sent in a regularenvelope. All samples must be clearly iden-tified with the horses’ registered name, num-ber and other required information. A copyof the registration papers should be enclosedwith the sample whenever possible.

Test results will be mailed to the owner orveterinarian, whomever is specified on theform. Results will not be given by phone.

Arrangements for testing can be madethrough APHA. Contact Field Services forforms and instructions.


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

BLACKEntire coat, including muzzle, flanks andlegs, are black; color may fade when exposedto the sun; could have rusty tinge during cer-tain times of the year; early foals may be anoverall mousy gray, then shed to black.

BROWNBody color brown or black, with light areasat muzzle, eyes, flank and inside upper legs;mane and tail usually black.

BAYBody color reddish brown, with variationsranging from dark blood bay to light bay andusually distinguished by black mane and tail, ear tips, lower legs.

BUCKSKINBody color yellowish or gold, mane and tailblack; black on lower legs; lacks primitivemarkings.

BLUE ROANThe overall intermingling of white hairs witha black body color; head, lower legs, maneand tail are usually solid or darker; does notget progressively whiter with age.

BAY ROANThe overall intermingling of white hairs withbay body color; head, lower legs, mane andtail are usually solid or darker; does not getprogressively whiter with age.

GRAYDominant over all other color genes; bornany color with white hair progressively turn-ing the coat whiter as the horse ages; darkskin; normally grays first around eyes andbehind ears.

PERLINODouble dilute of bay/brown resulting in bodycolor of cream or off-white; lower legs, maneand tail light rust or chocolate shade; skin ispinkish or grey; eyes are blue or amber; thecoat has enough yellow hue to allow whitemarkings to be visible.

GRULLOA form of dun with body color smoky ormouse-colored (not a mixture of black andwhite hairs, but each hair mouse-colored;mane and tail black; has black primitivemarkings.

DUNDiluted body color of yellowish or gold;mane and tail are black or brown; has blackor brown primitive markings.

CHESTNUTBody color dark red or brownish red; rangefrom very light to liver chestnut; liver chest-nut can be distinguished from black orbrown only by the bronze or copper high-lights on the legs; mane and tail usually darkred or brownish red, but may be flaxen.

SORRELBody color reddish or copper-red; mane andtail usually same color as body, but may beflaxen or very dark brown.

PALOMINODiluted body color varying from rich goldto pale yellow; mane and tail generally paleor off-white but may be same color as body(with nonblack points).

CREMELLODouble dilute of chestnut/sorrel resulting inbody color, mane and tail of cream or off-white with pale, pinkish skin; the coat hasenough yellow hue to allow white markingsto be visible; eyes are blue or amber.

RED ROANThe overall intermingling of white hairs withchestnut/ sorrel body color; head, lower legs,mane and tail are usually sorrel or dark red;does not get progressively whiter with age.

RED DUNA form of dun with body color yellowish orflesh-colored; mane and tail are red or red-dish; has red or reddish primitive markings.

COLOR DESCRIPTIONS


APHA Color Guide - Press

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