From The Horse Gazette Acrhives

Equine Color Genetics
- By Prism

Definitions of Terms and Genetic Chart
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