Coquat Ranch

If you are looking to purchase your first American Paint Horse Association (APHA) or Pinto Horse Association (PtHA) horse or just want to read up on some coat color material, I hope this page is of help to you.  I have included information on coat color and coat patterns and a small amount of information on coat genetics.

Coat color genetics is very interesting, but remember, you don't ride color!  Although, some knowledge of pattern genetics is necessary when breeding paints to avoid situations like the production of a Lethal White Overo (LWO/OLWS) which is discussed towards the bottom of the page.

Horses can be broadly classified into two base pigments:  Black and Red.

→Horses with a black base pigment mostly have black points.  Examples of these coat colors include black, brown, bay, blue roan, buckskin, grullo, and perlino.  The allele (E) represents the black factor and is dominant.  Therefore, horses that have black points can be represented by (EE) or (Ee).

Examples of horses with a black base pigment include Black Jack, Rio, Star, and Snowball.

Buckskin                                             Bay

→Horses with a red base pigment have red points.  Examples of these coat colors include sorrel (or chestnut), red roan, red dun, palomino, and cremello.  The allele (e) represents the red factor and is recessive.  Therefore, horses that have red points can be represented by only (ee).

Examples of horses with a red base pigment include Max, Diamond, Faith, and Roxie.

Sorrel                                            Palomino                                        Sorrel

»Horses homozygous for the black gene, like Black Jack, are represented by (EE) and will always pass one (E) to offspring.  In other words, they will never have red-based offspring.

»Horses homozygous for the red gene, like Roxie, are represented by (ee) and will always pass one (e) to offspring.  Skip's offspring can be (ee), red, or (Ee), black, depending on the stud.  This recessive allele, (e), can be overridden by the dominant allele, (E), if mated to a horse carrying a (E):  (EE) or (Ee).

• (EE) - black base pigment
• (Ee) - black base pigment
• (ee) - red base pigment

→These possibilities can be expressed in the form of a simple Punnett Square:

All crosses produce horses with black points.

Furthermore, the two base coats can be affected by dilutions and modifiers like Gray (G).  Gray is a dominant gene, which means all coats modified by gray (G) will lose pigmentation and eventually turn white in 5 to 10 years.  Homozygous (GG) horses will show more rapid graying and larger distribution of gray than heterozygous (Gg) horses, but both will "gray out". (g) is the absence of gray.  (gg) horses will not gray out.

• (GG) - homozygous dominant gray
• (Gg) - heterozygous gray
• (gg) - absence of gray

Badger is a great example of a gray horse.

Both gray horses and paint horses with pink pigmented skin, have a tendency to develop skin cancer around or after about 10-years-old.  A common area subject to skin cancer is the vulvar area or anal area under the horse's tail.  A lot of paints especially toveros and tobianos will have pink pigmented skin in this area.  Many gray horses will have pink skin, but a lot will have dark pigmented skin with a few lighter pigmented patches.

Painted horses can be broadly classifieds into 3 basic color patterns:  Tobiano, Overo, and Tovero.

→Tobianos usually have distinct characteristics:

• Dark coloring on flanks
• White legs
• Coloring and spots are distinct and smooth having a crisp edge
• Chest is colored and looks like a shield
• Markings on head resemble that of a solid horse
• Two-toned tail
• White will cross over the back

Examples of the tobiano pattern can be seen on Black Jack (TT), Snowball, and Ember.

Sorrel Tobiano                                                                Bay Tobiano                                Black Tobiano

The tobiano trait is dominant and is represented by (T).

→Overos usually have distinct characteristics:

• At least one of four legs will be dark
• White is scattered and splashy
• Markings on head include bald-faced, apron-faced, or bonnet-faced
• Solid colored tail
• White will not cross over back between withers and tail

Examples of the overo pattern can be seen on Max , Missy, and Faith.

Palomino Overo                                           Sorrel Overo

»The overo pattern actually consists of 3 separate patterns, which will be discussed further in the genetics section.

→Toveros, as the name implies, are a mixture between the two other patterns:

• Ears are colored and make a pattern that looks like a hat
• One or both eyes are blue
• Dark coloring around the mouth
• Coloring on the chest that may extend up the neck
• Flank coloring
• Coloring at the base of the tail

Black Tovero

If you want to breed for a unique pattern or try to avoid a particular outcome, you need to understand pattern genetics.

»The tobiano pattern is dominant (T) while non-tobiano is recessive (t).  This means that if (T) is present in a foal, (TT) or (Tt), the foal's pattern will be tobiano.  If a cross yields a (tt) foal, the foal is absent of the tobiano trait and pattern.  An example of a (tt) horse is Star.

• (TT) - tobiano
• (Tt) - tobiano
• (tt) - absence of tobiano

Most tobianos are heterozygous (Tt), but some, like Black Jack, are homozygous dominant (TT) and will produce painted offspring 100% of the time.  Testing for these genes will be covered further down the page.  (tt) is said to be homozygous recessive and describes no expression of the tobiano gene or pattern.

Black Jack (TT) x (TT) Mare             Black Jack (TT) x (Tt) Mare               Black Jack (TT) x (tt) Skip

                                                  
100% Chance of Tobiano Foal

Heterozygous Stud (Tt) x (Tt) Heterozygous Mare

75% Chance of Tobiano Foal

Heterozygous Stud (Tt) x (tt) Skip            Homozygous Recessive Stud (tt) x (tt) Skip
                                                
50% Chance of Tobiano Foal                                    0% Chance of Tobiano Foal

»The term overo describes 3 genetically distinct color patterns, but has been lumped together in 1 description through habit and convenience.

The 3 overo color patterns include the frame overo, the splashed white overo, and the sabino pattern.

→The frame overo usually has white patches centered in the body and neck with coloring around them.  An example of this can be seen on Max, Faith, and Missy (Missy is a minimal white).  The frame overo pattern acts as a dominant gene (nO).  Commonly, a frame overo mated to a solid horse will produce 50% painted (nO) offspring.  Some frame overos can be almost solid, lacking in spots, and will produce painted offspring 50% of the time.  Frame overos can also produce lethal white foals (OO).  By mating two frame overos, (nO) x (nO), there is a 25% likelihood a foal can receive both copies of the (O) gene.  If a foal receives two copies of the (O) gene, the foal is born white and will die of neural related gut abnormalities.  Blood typing and DNA testing can eliminate the possibility of lethal whites by providing the opportunity for responsible breeding plans.

    Max (nO) x (nn) Mare                                         Max (nO) x (nO) Missy                                                          
50% Chance of Frame Overo Foal                              50% Chance of Frame Overo Foal
                                                                            25% Chance of Lethal White Foal

Since the frame overo pattern (nO) does exhibit dominance, it is helpful in the production of the overo pattern in offspring.  The frame overo pattern is very desirable.  Breeding between (nO) and (nn) horses is 100% safe.  The only reason you need to be worried about lethal whites is if one horse you are breeding is (nO) and the other horse hasn't been tested.  In that case, testing the other horse by simple genetic testing can determine if the cross may produce a lethal white.  Production of lethal whites is 100% avoidable.

• (nO) - frame overo carrier
• (nn) - non frame overo carrier

→The sabino pattern describes horses with flecks, patches, and roan areas.  These horses usually have blue or partially blue eyes, four white feet and legs, a mostly white head, and a speckled coat.  A lot of deviance of these general guidelines occurs.  Sabinos can be pretty white and survive unlike lethal whites and are not currently associated with lethal whites.

→Splashed white is the least common coat pattern.  Genetic study of the splashed white is even newer than that of the frame overo.  Some evidence of deafness seems to be linked to splashed white horses.  No homozygous splashed whites have been documented and genetic defects have yet to be linked to this scarcity.  Splashed white horses often look like they've been dipped in white paint.

You may choose to have many different DNA tests performed on your horse.  DNA testing is simple and cost effective.  Several tests include Red/Black Factor (EE or ee), Tobiano Homozygosity (TT), Lethal White Overo (LWO/OLWS), Hyperkalemic Periodic Paralysis (HYPP), and Hereditary Equine Regional Dermal Asthenia (HERDA).  In most cases, testing is $25 to $40 a test and requires only a sample of the horse's mane or tail including the hair roots.

HYPP

• H/H - homozygous dominant HYPP affected horse showing severe symptoms
• N/H - heterozygous HYPP carrier showing minimal symptoms
• N/N - homozygous recessive normal horse with normal genes

HERDA

• N/N - homozygous dominant normal horse with normal genes
• N/H - heterozygous HERDA carrier with no symptoms
• H/H - homozygous recessive HERDA affected horse showing symptoms

You can visit sites like Pet DNA Services of AZ and Animal Genetics Inc. or shop around for less expensive testing.

If you are thinking about breeding your mare to a (nO) frame overo, you should have your mare tested for the (O) gene.  Just because she is an overo does not mean that she will be a carrier, but you must remember that even solid horses can be carriers for the gene.  Even though mating (nO) with (nO) only has a 25% of producing a lethal white, anything more than O% should be enough to sway that decision.  You should never mate two carriers together.

Why not?  Well, what is a lethal white?  A lethal white foal is a foal whose intestinal system has not developed proper neural pathways.  The foal will be born almost pure white and will die at about 72 hours after its first meal has not been properly digested.

In saying that, it is not a horrible thing to have a carrier.  It can be a positive thing as the offspring will be 50% overo and most likely painted.  If the dam or sire is (nO), that does not mean that the offspring will be (nO) even if they are painted especially since tobianos can be (nO).  Frame overo is a desirable coat pattern especially in riding horses, show horses, and event horses because it is flashy.  Careful breeding will create beautiful horses and will avoid lethal whites.

Another important thing to remember is that sometimes your tobiano mare or stallion may be a carrier.  Not all (nO) horses are frame overos, much less overos at all.  They can be tobianos, and rarely, solid AQHA quarter horses, mini horses, and even thoroughbreds.  The overo gene is independent and devoid of the tobiano gene.  The tobiano gene may show in your tobiano horse while the overo, (nO), remains hidden phenotypically, or visually.

The two different traits, Tobiano and Overo, may appear on either different loci on the same chromosome or on two different chromosomes:

 ♂  ♀       or        ♂  ♂    ♀  ♀
      

So, the offspring could end up with (E) and (O).  If you tested the horse for the tobiano allele, this might deter you from testing for (O).  Tobiano horses and solid horses can still be (nO) and therefore potentially produce lethal whites and should be tested for the LWO trait if breeding with a (nO) stud or mare.

• (TTnO) - homozygous tobiano with frame overo gene
• (TtnO) - heterozygous tobiano with frame overo gene
• (ttnO) - tobiano absent with frame overo gene
• (ttnn) - tobiano absent with frame overo gene absent
• (TTnn) - homozygous tobiano with frame overo gene absent
• (Ttnn) - heterozygous tobiano with frame overo gene absent

I hope this has helped to either better inform you or to clear up a few things that may have been a little fuzzy.  As more research is done on coat color and coat pattern genetics, I am sure things will get much more complicated.  What? ...Did you think it would get any easier?

The American Paint Horse Association has some great information on their website in the form of PDF files and can provide you with some great brochure information as well.

In addition, genetic testing web sites have very accurate information.