From The Horse Gazette Acrhives

Equine Color Genetics
- By Prism

Definitions of Terms and Genetic Chart
Updated: 9/25/20

Dear Prism,
Hi! I am a breeder of Shetland ponies and I work with the silver gene frequently. Silver bay is the result of the silver gene acting on the bay; it lightens the mane and tail to varying degrees of flaxen; the black points of bay turn mouse-gray and the body stays red. Most of these are misidentified as sorrels and chestnuts. Many silver-bays were produced by breeding bay hackneys into the silver dapple Shetland stock (also known as silver black or chocolate silver). It is also interesting to note that red masks the silver gene so it can pop out of a red parent. Hope this helps your question about silvers. Jackie

Dear Jackie,
Thank you so much for this explanation of the Silver Dapple genetics. I'll be the first to say I know very little about the effects of this gene on coat colors. Your knowledge is appreciated and it answers several questions readers have had on the Silver gene. Prism

More on the Silver Gene

Dear Prism,
Ok, I have a Sorrel mare that is out of sorrels (as far as I remember) I bred her to a breeding stock paint black/bay stud 3 times. I got a tri-colored, a sorrel solid, and what looks to be red roan paint. Ok, he is light, light red with white hairs through out. I would say he is a roan but his legs on the back are white stockings. His front legs are the same as his body. So what is he? His head is the same as his body but with a bald white face. Also I bred this same mare (that obviously has 2 red genes) to a homozygous (true) black/white. He has 4 foals on the ground and they are all black and white or bay and white. The last colt was out of a really light red and white mare and is black and white. What are the chances of my foal being dark (black, bay, copper) and white foal. My mare is due soon and I'm just curious.

I also have one other question on a mare that I own. She is a liver chestnut and is said to be a pass through mare. Her only baby was pretty much hair-for-hair just like her father (a paint). Is there such a thing and what are the chances of that happening again. Laura

Dear Laura,
Your mare, being sorrel, does carry 2 red genes and if bred to a sorrel will produce only sorrels.

The bay colt she had from being bred to a bay stud is the result of the foal getting the black gene from the sire.

The roanylooking colt may be exhibiting effects of the Sabino pattern. First rule of roans is: A roan foal must have a roan parent. Many paints are called roan; when they have Sabino characteristics. Remember a roan will have a solid head, legs and mane/tail (no white hair) with the body being a 50/50 mixture of white and colored hairs.

On breeding the sorrel mare to a homozygous black/white;is the stallion homozygous for the black coloration? Four foals is not a large enough produce record to make a safe assumption as to the color. If the foal inherits a black gene from the sire; it will be black, brown, or bay. Since the stallion is black/white, we know he doesn't carry the Agouti (Bay) gene. So for you to get a bay from this cross, the mare would have to give the foal the Agouti gene. The Agouti gene is only hidden on red horses as it only affects black color. If the stallion is truly homozygous for the black gene then all of his offspring will be black, brown, or bay and he will never sire a "red" foal. If he is not homozygous for black, then you will have a 50% chance of the resulting foal inheriting the black color.

On the "pass thru mare." I have never heard of that. There are those mares which are not a predominate breeder and simply don't stamp their foals. But essentially, you have a 50% chance of the foal inheriting more characteristics from the stallion than the mare. There has bee no scientific research to explore this possibility in equine breeding. Prism

Updated: 7/12/20

Dear Prism,
If I have a buckskin mare and want to breed her what color stud do I breed to get a buckskin foal. Susan - submitted via

Dear Susan,
Let's define "Buckskin" first. Buckskin is a bay horse with one copy of the Dilute/Cream gene. And a bay horse is a black horse with Agouti (limits the black color to the mane/tail/legs). Being buckskin we know your mare is black-based, carries at least one copy of the Agouti gene and carries one copy of the Dilute/Cream gene. We don't know the status of her Black and Agouti genes (one copy of each or two copies of them). Since we don't know her Black or Agouti status you could get the following if you breed her to a Bay stallion - Sorrel, Palomino, Black, Smokey Black (a black that carries the Dilute gene), Bay or Buckskin. T here are a whole lot of unknowns in your question. Not knowing her status, I'd breed her to a bay stallion and hope she passes the dilute gene to a bay foal. If you breed her to buckskin you could get the approximate following percentages; 25% Bay, 50% Buckskin and 25% Perlino. - Prism

Dear Prism,
We are going to breed our chestnut w/flaxen mane and tail to a gray stallion. What will the offspring color be? Thank you! Briana, submitted via

Dear Briana,
That will depend on the stallions "Birth" or "Base" color. All gray horses are born a different color and turn gray with age and right now we don't know what the stallion brings to the breeding pool. All Chestnut/Sorrel horses are homozygous for the red gene and will always pass a red gene to foals. So any color besides "Red" will be up to the stallion. If he was born Bay or Black then you could get almost any color for the foal. If he was born Chestnut or Sorrel then the only color you will get would be "Red". The only firm, given fact in breeding horses is "If you breed a "red" horse to a "red" horse you will get a "red" horse." - Prism

Updated: 3/23/20

Dear Prism,
I have a dark bay or (brown as it says on her papers) QH mare. If I breed her to a cremello stallion what possible color foal could she have? I know once when her previous owners had her they bred her to a palomino stallion and she had a beautiful sorrel with silver (not flaxen) mane and tail, blaze face and four white stockings. Tks, Mike

Knowing that your mare produced a sorrel lets us know she is hetrozygous for black (carries 1 black gene (she's a dark bay/brown) and 1 red gene. We know that a Cremello is homozygous for the red gene as Cremello is a sorrel with 2 dilute genes. We also know the Cremello is homozygous for the Dilute/Cream gene. So breeding to a Cremello guarantees one of three colors; Smokey Black (a black that carries 1 dilute gene), a Palomino (red base/sorrel with 1 dilute gene) or a Buckskin (Bay with 1 dilute gene. Only three colors possible when breeding to a Double-dilute. - Prism

Dear Prism,
I have a sorrel mare with a cream gene. If I breed her to a grullo, what are the color combinations I could get? Thanks, John B

I'm a little confused - are you sure the mare carries a cream gene? If she did she would be a Palomino and not a sorrel. Grullo is a Black with the Dun genetics. To answer your question, I'm going with the phenotype you gave me; Sorrel. Breeding a Sorrel to a Grullo could result in the following foal colors; Sorrel, Red Dun, Bay, Classic Dun, Black or Grullo. - Prism

Updated: 3/18/20

Dear Prism,
Hello. I have an AQHA filly that was born red dun with all of the dun factor characteristics (red leg barring, dorsal stripe, red mane and tail). Now, as she is shedding her baby fuzz, she is black underneath. She has three white stockings, and so far I cannot see any black coming through near her coronet band on her solid colored leg. However, every place else on her body where there is a nick or scrape, she looks very black. Where she is shedding out around her eyes and muzzle, she is almost black. The sire was a dun with black points, and the mother was a brown/black out of a black sire and sorrel mare. Any ideas? Thanks for your insight. – Submitted by Melissa K. Miller via

Dear Melissa,
Congratulations! You have a “Surprise Package”. One of the reasons I love foals so much as one rarely knows what they’re getting until the yearling coat shed off. Since both parents are black based they obviously carry a red-gene each (the filly was born Red Dun). Without pictures I really can’t take a learned guess but I’m going to say you’ll end up with a shade of red, won’t comment on the “Dun Factors” as many foals are born with what looks like Dun factors but are in fact Counter shading. I will say if she was going to be black based, the solid leg would be showing black color. - Prism

Dear Prism,
What colour stallion should I breed to a black mare to get a dun or grullo foal? I think that the mare may be heterozygous for black as her body fades to dark dun in summer (including dark golden flanks, and she has red lights in her mane and tail, although her points remain black. Also is it true that the agouti gene is dominant, so if a horse has received it from only one parent, it will affect the colour, but it will not necessarily be passed on to the offspring? Submitted by Tracy via

Dear Tracy,
You would need to breed to a Dun stallion to introduce the Dun genetics/markings into the mix. You would still have a 50% chance of the resulting foal being a dun. As far as the black status of the mare - easy way to know is to have her tested. Pull mane hairs and send to a lab for the 'Red Factor Test'. The test will let you know if she carries the red gene or not. As far as the Agouti? Agouti only affects the black color so many red horses carry agouti but you would never know without testing. And yes, Agouti is a dominant gene and just one copy will give you a Bay horse instead of a Black horse. As with all genetics - when one copy of a gene is present there will be a 50% chance of that parent passing along to the offspring. - Prism

Dear Prism,
I have a filly whose dam is palomino and sire is black/bay. The filly is a very light sorrel with lighter legs belly and chest. I have seen pictures of foals this color that are advertised as palomino. How do I know if my filly will turn palomino or stay sorrel? Submitted by Bridget via

Dear Bridget,
Easiest way it to have her tested for the Dilute/Cream gene. The filly had a 50% chance of inheriting the dilute/cream gene from her mother. Another way would be to look at the mane/tail of the filly - if she is a Palomino the mane/tail should be an extreme flaxen or white color. I've seen many different horses of different breeds advertised as Palomino when there was no way they could be - I'd test her to know for sure. - Prism

Dear Prism,
I have a Grullo Stallion and I'm not sure if he is heterozygous for the black gene or not, since I have not had him tested just yet. What color mare would I have to breed him to in order to get another grullo? Just the same, what are some other possibilities for his breeding with other colors? Submitted by Krista Rougeux via

Dear Krista,
Well, Grullo is Dun on a black base with no Agouti present. Since you don't know his red status we will assume that he carries a red gene as well. Your best bet to get a Grullo foal would be to breed him to Grulla mare. The mare would also be Dun on a black base with no Agouti (which limits black to the points). This should also minimize chances of a red foal as well. If your stallion is homozygous for black you will never have a red foal regardless of the mares he is bred to. So your color possibilities for foals out of your stallion would be Sorrel/Chestnut, Red Dun, Black, Grullo, Bay, Bay Dun, I'd have him tested so you know exactly what you are dealing with in the breeding shed. - Prism

Dear Prism,
I have a chestnut mare that I'm breeding to a buckskin Appaloosa that throws 100% color/characteristics. What color possibilities are most likely? - Karen, submitted via

Dear Karen,
Well the base color of the upcoming foal could be a Sorrel/Chestnut, Bay or Black. If the stallion passes his dilute/cream gene the foal could be Palomino, Buckskin or Smokey Black. It also sounds like the foal would be marked like an Appaloosa. - Prism

Dear Prism,
I have a sorrel mare that is a twin. Her twin is a red roan gelding. I breed her to a gray stud that was born brown. What colors are possible? - Tammy, submitted via

Dear Tammy,
We know that sorrel is homozygous for red and recent research in France has acknowledged that “Brown” is a form of Black. That means your foal could be Sorrel, Black, Brown or Bay and there would be a 50% chance of the stallion passing along his gray gene. - Prism

Dear Prism,
Do you know what foal colors to expect if I breed a buckskin mare to a bay stallion. The stallions parents were both Grullo. Also, Is having a mare for breeding HYPP/NN a horrible thing or should I stay away from the impressive lines. Thanks, Lazy M Ranch, submitted via

Dear Lazy M Ranch,
There are a number of variables at play here – if both horses are heterozygous for the black gene (carries one copy) then the foal could be red-based (Sorrel). If one parent is homozygous for the black gene you can rule out red so you’d get a Bay or black. Factor in the dilute/cream gene from the mare and you could get a Palomino, Buckskin or Smokey black. We know the stallion did not inherit the dun gene from either of his parents or he would be a Dun and not a Bay.

And the second part of your question will open a whole can of worms. So what I’m going to say is my opinion and my opinion only.
Impressive bred horses are not a bad thing. They are some of the most athletic horses I’ve ever been around and most of them are flat out beautiful to look at. Impressive is actually one of my favorite bloodlines.

HYPP is the “Bad” thing, not the Impressive bloodlines. I think it is a shame that folks will throw out the baby with the bathwater and declare a whole “family” of horses as bad because of a genetic defect in a few.

HYPP is the genetic defect and it is not a disease. It prevents sodium (potassium) from passing through the muscle membranes and creates an overload of Potassium in the horse’s body. Too much Potassium causes paralysis of muscles and leads to possible death of the horse. There is no cure for a genetic defect and the best owners can do is treat the symptoms. Horses can not “catch” HYPP they have to be born with it. If breeders would stop (as in QUIT) breeding HYPP positive animals the entire species (equid) could be rid of HYPP in one generation.

But most importantly a horse that is HYPP N/N does not have HYPP, will never catch HYPP and will never have offspring which are HYPP positive unless you breed to a HYPP positive horse (and then the HYPP will come from the Positive horse and never from the HYPP N/N horse).
If you like the Impressive bred mare and she brings everything you want to your breeding program then breed her. But don’t be hesitant about breeding an Impressive bred horse which is HYPP N/N because that mare will never pass HYPP to her offspring – she doesn’t carry it. - Prism