Last Updated on January 21, 2022
Horses are one of the most exquisite-looking animals. Whether they are dapple gray, strawberry roan, or anything in between, their beautiful coats catch our attention. Every horse color genetics work to create a beautiful coat.
When breeding horses, it is important to understand color genetics. Color genetics allows us to comprehend what coat colors a horse can produce and what abnormalities it may have.
There is much for us to understand when it comes to horse color genetics. Certain desirable coat colors are caused by mutations that can cause negative side effects for the horse. There are even breed and color organizations that have restrictions based on coat colors and patterns.
Horse Color Genetics: Understanding Coat Colors
There are three basic coat colors for horses: bay, black, and chestnut. These coat colors are determined by the interaction of two genes. Every other color is a variation or lack of those basic colors.
There are several different coat combinations that can be produced by genes and their alleles. Understanding horse color genetics can be tricky, but learning them can help you comprehend your horse’s genetics better.
There is a duplicate set of genes in every cell, one from each parent of the horse. Alleles are the alternative form of a gene. If a horse has two copies of the identical allele for its gene, then the horse is homozygous. If there is one dominant and one recessive allele, then the horse is heterozygous.
Every basic coat color of a horse is either W, G, A, or E genes.
Gray horses are born either GG or Gg. Gray is produced by a dominant gene, so every gray horse must have at least one parent that is gray. Unlike horses with the W gene, G horses are born with pigmentation. If a horse is born with a G allele, they aren’t born gray, but their hair will turn gray as they age.
A horse with the W gene lacks pigmentation in the skin and hair, therefore making the hair white. Horses with this gene are not common and have pink and either brown or blue eyes. Horses that are albino have the W gene.
Gene E and A
The Extension gene (E) is what allows black pigmentation and the gene Aougti (A) determines where the black is on the horse’s coat. These genes are what make up bay coats. All horses that are bay or black have at least one copy of the E allele. Allele e is the alternative to E and produces a black pigment in the skin instead of the hair.
In a horse that has the genotype E/E or E/e, the A gene is the determining factor for a horse to be bay. The pigmentation produced by e allele is what causes red hair to appear.
If a black horse is homozygous E/E, it will always produce offspring with a black base to its coat. Horses that have E/e can produce offspring with either red or black base to its coat. Chestnut is a recessive trait, so all horses that are chestnut are homozygous e/e.
Gene C, along with allele Ccr, creates pigment dilution in a horse’s coat. Horses that are CC have full pigmentation. Horses that have CCcr have black pigmentation and red pigment that has changed into yellow. Gene C and Ccr are the contributing factors that create buckskins, palominos, and cremellos.
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Gene D is very similar to Ccr, as it produces a similar dilution in a horse’s coat. D dilutes both red and black coats, however, it does not dilute pigments at the points. The D gene is what allows horses to develop dorsal strips, shoulder strips, and leg barring. The gene D is not found in many breeds of horses; however, D can be found in some American breeds such as the Quarter horse.
Horse Color Genetics: Gene TO
Despite the many different spotting patterns found in horses, tobiano is the only pattern known to have a distinct gene. The tobiano coat color is defined by a pattern of white hair with pink skin. Tobiano’s typically have dark heads (minus facial markings), white legs, and white generally on the neck and back.
The LP pattern is the spotting pattern found in Appaloosa’s coats and is an incomplete dominant trait. Scientists have not yet discovered what causes the Appaloosa’s patterns, but it has been traced to a mutation. However, it is known that Appaloosa’s can face mutations in their genes and develop eye issues which can lead to a lack of night vision.
Dilutions in genes make the coat lighter in appearance. The cream dilution creates the palomino, cremello, buckskin, perlino, and certain smoky coat colors. Other dilutions include champagne, dun, pearl, silver, and dun.
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Horse Color Genetics: Other Colors
Colors such as sabino, splashed white, and overo are forms of spotting patterns. A horse that has a mixture of white and dark hairs are roans. Brindle is a rare coat that can either be inherited or non-inherited.
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Certain unique coat colors that look beautiful unfortunately can produce some unwanted side effects. Though brindle coats are rare, certain forms of the brindle coat cause male horses to die as an embryo. Homozygous overoes are born all white with blue eyes and sadly suffer deadly intestinal complications; and silver can result in equine multiple congenital ocular anomalies (MCOA), which causes developmental abnormalities within the eye.
Horse Color Genetics: Learning More
Horse genetics are complex and there is much to understand about them. Researchers are still learning more about different genes found in horses and what abnormalities may come along with certain colors.
If you want to know about your horses’ genetics and what color offspring they can produce, there are tests available to discover their genetic makeup. Not only are horse coat colors beautiful, but they tell us a lot about horses.
Feel free to comment any questions you may have, as horse color genetics is a complex subject.
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Michael Dehaan is a passionate horse owner, horse rider, and lover of all things equine. He has been around horses since he was a child, and has grown to become an expert in the field. He has owned and ridden a variety of horses of different breeds, and has trained many to compete in shows and competitions. He is an experienced horseman, having worked with and competed many horses, including his own. He is an active member of the equestrian community, participating in events and teaching riding lessons.