Tuesday, August 5, 2008

Color Genetics

Other than reining, cutting and cowhorse bloodlines, one of my favorite horse topics to study is color genetics. I am astounded at how often people mistake the color of their own horses. Some have even paid a premium for what they thought was a blue roan (that is actually a gray) or bought a "palomino" that is actually a sorrel with flaxen mane and tail. I will admit to being stumped a time or two myself. It doesn't help that the definition of a color can vary from one breed association to the next or that at times you need to use genetic testing to determine the true color. When I began my quest to better understand color genetic I found that some websites provided to much scientific information or made things overly complicated while others got their facts wrong. I would like to explore color genetics in today's entry to see if I can get the basics across in a simple and easy to understand format. I wont delve to far into the science of color or the rare genes and combinations but instead will try to change the way you see a horses color by understanding the basics of how they come to be.

To start:

1: It is important to understand that all horses are essentially either black or red underneath whatever color they appear! Bay, buckskin, palomino and grulla, are all black or red horses with extra genes that change how they appear. Even gray horses are black or red underneath. I like to think of a horses color as a layers of paint that always start with a primer of red or black. Some do not get any additional colors genes (layers of paint) added. Red horses are simply that. Red.

Red- these include all shades or chestnut, sorrel, liver, cherry, sooty, etc. These horses do not have any black on their bodies (some dark chestnuts can appear to have black manes and tails but they are really a deep dark chestnut).

Other horses are simply Black: A true black horse has no brown on his body unless his usually black coat has been damaged by the sun. He always has a black muzzle and flank. Many dark bay horses are mistaken as being black.

2:- For the sake of simplicity, we need to consider Bay as a base color even though technically, Bay is dilution gene effecting a black horse. It is easier to understand the other color genes that change a base color if you consider Bay a base.

Bay- It causes the body of the horse to lighten to varies shades of brown while leaving the points (feet, mane and tail) black. From horses with only brown muzzles or flanks all the way to a light russet or blood bay, as long as there is brown somewhere on the body and the points remain black, a horse is considered bay.

Now that we understand the three base colors we can explore the other genes that create the beautiful array of colors we find in horses today.

3: One of the most common genes that effect the color of horses is the Creme gene. It is a dilution gene which means that it lightens the coat color. When you apply the Creme gene to base coat of:

Red- you get a Palomino. This causes the mane and tail to become white and generally for the body to lighten to a deep to light honey color. If the base color of red was a deep chestnut, sometime this will result in a chocolate palomino (mane and tail white while the body is a milk chocolate color).

Bay- you get a Buckskin. This causes the body to lighten from sooty brown to a light or dark honey color but the points (mane, tail and legs) remain black. Distinguishing a Bay from a Buckskin can be so difficult as to require genetic testing. While some are obvious with a honey colored body and black points, other can be a deeper brown color to appear almost bay.

Black- you get a Smokey Black. This can cause the black coat to lighten while the points generally remain black. Smokey Blacks are generally hard to recognize and again are often mistaken for bays without genetic testing.

The Creme gene is unique in that when it appears in its homozygous form (a horse that received a creme gene from both parents and therefor carries two) it physically presents itself as a different color than in it heterozygous form (single gene.) When two creme genes are present on a:

Red- it creates a Cremello. These horses are a soft creme color and have two blue eyes, no dark patches and pink skin.

Bay- it creates a Perlino. Perlinos also have creme colored coat, two blue eyes, no dark patches and pink skin. Generally they have slightly less creamy coat color and almost have a bluish sheen. Genetic testing is generally required to distinguish between a perlino and cremello.

Black- it also creates a Perlino but has no Bay gene.

What is unique about cremellos and Perlinos is that they must pass on one creme gene to any foal they produce. A cremello/perlino will therefor always produce a buckskin, palomino or smokey black when bred to a Red, Bay, or Black horse. If a cremello/perlino is bred to a horse that already carries a creme gene (buckskin, palomino or smokey black) there is a good chance that both parents may pass on their creme gene, resulting in a cremello/perlino foal. If two cremello/perlinos are bred together the resulting foal will always be a cremello/perlino. For this reason cremello/perlinos are often desired breeding stock because they will always produce the more desired buckskin/palomino or smokey black colors. It is possible for a cremello/perlino to also carry the dun, roan or paint genes but they always appear creme in color.

It is always important to remember that a horse can have more than one color gene on top of his base color of Red, Black or Bay.

4: Another common dilution gene is the Dun gene. Dun also lightens the body color but also ads what is called Dun Factor.

Dun Factor are markings such as a dorsal stripe (dark stripe that runs down the back from wither the tail), Shoulder Barring (a dark shading that runs over the wither), Zebra Striping (darker lines or stripes that appear on the upper legs), Face Mask (darker shading on face that may have a cobweb pattern), Guard Hairs (silvery hairs on the top of the mane and tail) and Dark Tips to the ears. A Dun will have one, some or all of the above markings.

When you apply the Dun gene to:

Red- you get a Red Dun. Red duns do not have any black points on their body and any of the Dun Factor they present appears in a deep red color. Their bodies can be any shade of red but generally appears as a lighter honey red body with dark red mane, tail and legs.

Bay- you get a Dun. Dun can range from a light honey, to a rich chocolate but the points always remaining black and the Dun Factor always presents as black.

The horse pictured at right shows an unusual amount and prominence of Dun Factor but this example functions well in demonstrating where each is located. Usually duns have a thinner dorsal stripe and much lighter barring at the shoulder.

Black- you get a Grulla (sometimes written as Grullo or Grullya) This color is another that is commonly misunderstood. The black body turns anywhere from a light silver to a mousy gray, or dark blue. It is a striking color and often sought after by breeders. The points must remain black. A dark face and little white is considered desirable. The body can appear a browny color in which case genetic testing is required to determine if the horse has a bay gene (and is therefor dun) or if the horse is genetically black (and therefor a grulla).

The dun gene may also appear in a homozygous form (a horse with two genes of the same kind) but in Duns, there is no physical different between a homozygous or heterozygous (caring one gene) duns.

5: It is possible and not uncommon for a horse to have both a Creme gene and the Dun gene. When you apply both to:

Red- you get a Dunalino. The body is lightened to a striking yellow honey, almost pink color and the mane and tail become white. The horse presents Dun factor in a darker shade of honey. Personally, this is my favorite color.

Bay- you get a Dunskin. Generally a horse with both the creme and dun gene will present as what is called a buttermilk dun. The body is lightened to the color of buttermilk while the points and Dun Factor always remain black. It is possible for a horse to be a darker dun color and also carry the creme gene.

Black- I cant find a name for the Dun + Creme gene on a black horse but it does generally present as a softer smokey colored grulla or silver grullo.

Six: Gray- generally horses that are gray become progressively "white" over age. Some go "white" earlier than others. Gray horses can range from a soft rose color gray (horses with a red base) to a dark charcoal color (black). They often are born with a fairy solid Red, Bay or Black coat with white hairs flecked throughout. As they age the gray flecking becomes progressively more dominant. Gray is an extremely dominant gene and so most gray horses will produce gray foals. A gray horse can have any variety of other color dilutions but Gray is always the most dominant and will eventually turn the horse gray.

7: Roans- roans are most commonly confused as grays or vise versa. The distinguishing difference between a Gray and a Roan is that Roan horses do not have white flecking on their their points (mane, tail, and legs) and the face is always solid in color (white markings are allowed such as blaze, strip etc. but solid is preferred.) The white flecking can range in density to create a coat that is almost silver in color to one that is fairly dark with a moderate amout of white hairs (so long as they are distributed evenly.) Where the skin in scared, the white hairs do not grow back in and so Roan horses often show dark marks over their body in the color of their base coat. When you apply a Roan gene to:

Red- you get a Red Roan. The faces, legs and tails remain a solid red color while a consistent degree of white hair fleck the entire body of the horse (as shown at right).

Bay- you get a Bay Roan. Most people do not recognize the difference between a true Blue Roan and a Bay Roan. A Bay roan has dark legs and black mane and tail but usually have a brownish hue to their coat and their solid faces show brown. (shown at left)

Black- you get a Blue Roan. Blue Roans are striking horses with a bluish tone to their coat. Their faces and points are always solid black. The bodies appear a silver blue.

There are many different genes that will effect the appearance of a horses color. Some include champagne, silver, pearl, robicano, flaxen, and all the various blanket patters of Appaloosas'). And many, many more! The rule of a base of Red, Black or bay still always applies.

I will only go into Paint Horses briefly. Paint horses(horses with patches of white on them) can be very difficult to classify but the general rules still apply. The horse always has a base coat color that is Red, Black or Bay with any number of Dun, Creme, Roan, etc. coats on top PLUS a gene that causes white patches that cover varying amounts of the body. I will pull this info from the governing body of Paint horses, the American Paint Horse Association.

Tobiano- the dark color (or non-white) usually covers one or both flanks. Generally all four legs are white, below the hocks or knees. Generally the dark color appears as ovals or round patters on the chest. The head is always solid with a normal face marking (stripe, blaze, star). A tobiano can appear as predominant dark or white. The tail is generally two colors.

Overo- the white will not usually cross over the back of the horse between the withers and tail. Generally one or all four of the legs are dark. Generally the white is irregular and is rather scattered or splashy. Head markings are distinctive with either bald face (large white blaze), apron faced (white extends around muzzle) or bonnet faced.

Tovero- Dark around ears, may extend down forehead and over eyes. One or both eyes blue. Dark around mouth that may extend upward. Dark on chest, may extend up neck. Dark patch on flank. Dark patch at base of tail. The rest of the body is white or may have small spots of dark.

I hope that this brief (I guess that is a matter of opinion) outline of horse color genetics will help you approuch the subject with a better understanding in the future. What is your favorite color?


  1. I'm glad that you like studying color patterns in horses, cause I HATE it. It is one thing about horses that I hate to study and learn. I don't know why but it just drives me crazy. Sure I know the basics of color and such, but any further questions I know who to direct them to.

  2. lol, it is funny how different people can be even when they share a common interest! I am a sucker for a colored horse! My favorite is a dunalino. I also love blue roans and grullas. Okay, so I love'em all. I want to put together a chart that shows what chances you have of producing a certain color when you breed two horse.

  3. Interesting post...

    I'm interested in colour a bit, but not an expert by any stretch.

    You did a good job of explaining the differences.

  4. Where I get lost is when the letters are added in for all the modifiers etc. With Arabian horses only being the basic colors anyway, I don't really need to know all that stuff anyway. I imagine I would know it, if I needed to though. LOL

  5. I have been searching for a long time trying to find genetic colouring in simple terms that I can actually understand, you have done a fantstic job, thankyou!!!