Black Genetics for Dummies

CAUTION - there are MANY "black" Andalusians that have not been tested to verify if they are truly black (E_aa)... use caution when breeding or buying!!!! We warned YOU! Verify the color using UC-Davis dna-results. 

by Donna DeYoung.

Please brush up on your Mendelian genetics and learn how to derive a Punnett Square! This is the minimal knowledge needed to be able to truly understand equine color genetics.

Here is a good article on the Punnet Square

Here is a Punnet Square calculator!

Mendel’s Law of Segregation

Easy to read article on Genetics

Still can’t figure it out? Here is an online color predictor for horses

Horse Color Genetics for Dummies

So, to start with … there are two basic coat colors of horses. A horse is either red or black. Period. That’s it. Easy!

Red pigment vs. black pigment. Red is chestnut or sorrel. Black is black.

If a horse is to have a base red color, he will be “ee” and has two recessive alleles. 

If a horse is to have a black base color, he will be Ee or EE and have at least one copy of the dominant allele E (also known as extension). The presence of E makes all his pigment look black instead of red. Big difference. 

A horse’s genotype is what is on the inside, in his genes. A horse’s phenotype is what you see, what color he appears on the outside. Some colors are caused by “hidden” or recessive alleles. Such as when a black horse carries a copy of little e for red. Breed two of these apparently looking black horses Ee x Ee together, and out could pop a chestnut horse ee. That is how genotype works. Note that with Friesian horses, almost all Friesians are EE, so that’s why you never see a chestnut Friesian. Not enough, if any, carry the little e. Because it takes two horses both carrying the little e to make a chestnut. Also note that there are A LOT of chestnut (sorrel) quarter horses. That’s because 100% of the time when you cross a chestnut with a chestnut (ee x ee), you get a chestnut. Regardless of whether they have the agouti gene (discussed below) because agouti does not affect chestnut. 

Now enter the Agouti gene. Agouti is a dominant allele and it reacts with black pigment only. It causes the black that is normally spread all over the horse (a solid black) to restrict itself to the points of the horse (ears, muzzle, tail, mane, legs). Thus the result is a BAY horse! A bay is a black horse with at least one copy of A. 

So, what is a black bay? There are other modifiers such as smutty or sooty that add black hairs BACK into the body of a basically bay horse. But that horse still genotypes as E_A_. In other words, it is a bay (that looks like a black). 

So what is a grey horse? A grey horse could start out as a red or black horse. But because it inherited even one copy of the grey modifier, the hairs will slowly grey out over time. Such a horse would be considered to be a “base” color, either red or black (or bay or buckskin, etc). But is a grey. 

There are only two black genotypes: 

EEaa – “double homozygous” black. This horse can never have a chestnut offspring and when bred to black will always produce black.

Eeaa – “homozygous black”. This horse is basically black, but also carries little e for chestnut. Possible this horse could produce a chestnut. 

There are several bay genotypes: 

EEAa – can never produce chestnut, sometimes can produce black

EeAa – can produce chestnut or black when bred to the right horse

EEAA – can never produce chestnut or black no matter what bred to. Will produce bay 

There are several chestnut genotypes:

eeAa – horse can produce chestnut or black, and sometimes bay (if other parent is not chestnut, contributes E)

eeAA – horse can produce chestnut but never black, and sometimes bay (if other parent is not chestnut, contributes E)

eeaa – horse can produce chestnut or black, and sometimes bay (if other parent is not chestnut, contributes E) 

A grey horse is either Gg or GG and can be any of the above genotypes in combination  

GgEEaa – horse is basically black and can produce grey or black

GGEEaa – horse is basically black but can only produce grey


Skyhorse Ranch - Andalusian horse breeder in Texas with Andalusian horses for sale. Breeders of PRE Pura Raza Espanola horses with cartas from Spain. Selling black, grey, and bay Andalusians. Recommend Andalusian stallions at stud. Pictures, history, facts, and info. Spanish Andalusian horse farm. Bloodlines from Spain in the USA.

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