Tuesdays with Tony

Equine Genetics

Boy, did I get schooled on Thursday when Dr. Brooks came to speak at our Genetics Seminar! I always considered myself a pretty smart cat, but I may have been knocked off my pedestal by that presentation. The information Dr. Brooks shared with us was not only mind boggling, but also fascinating. I’ll do my best to re-cap, but really, you should sign up for her online class at UF to hear it straight from the horse’s mouth (pun intended).

Science and stuff: The Basics

Every species has its own genome. That’s basically a map of genes, which are made up of DNA, that determines everything about an individual (hair color, height, weight, conformation, intelligence, athletic ability, personality, etc.) Alleles are different forms of a gene that are responsible for heritable traits. Horses (and humans) inherit one allele from their mother and one allele from their father for each trait.

Let’s look at eye color as an example. At one site on a gene (or locus) there are 2 different alleles for eye color, we’ll call them B and b. B confers brown eye color, while b confers blue eye color. B is dominant over b. If the sire and the dam both have brown eyes with genotype Bb, their offspring will theoretically be 25% BB, 50% Bb, and 25% bb. Since B is dominant, the foal will have a 75% chance of having brown eyes, and a 25% chance of having blue eyes. In reality, it is not quite this simple, as there are multiple genes that affect eye color. Also, I’m not a cat geneticist.

Genetics of coat color

Horse coat color is multifactorial (determined by several different genes) but we do have the knowledge to predict the possible coat colors we could get based on the genotypes of both parents. About 5,000 years ago, all horses were Black or Bay. How boring, right? But then a spontaneous mutation in a gene named KIT occurred, which resulted in cool white spotting patterns. Humans, being attracted to new and unique things, thought this was pretty neat so we kept it. That is, our ancestors collected the mutant white-spotted horses and bred them, resulting in more white patterned horses. This is how Sabino, Roan, and Tobiano coat patterns all came about.

The next question I asked Dr. Brooks was ‘OK, so how did Dr. Lacher get a Chestnut foal out of 2 Bay parents?’ I know Bay (Black allele “E”) is dominant and Chestnut (Red allele “e”) is recessive. She explained that just like in our eye color example above, the possibilities for a foal of two Ee parents would be 25% EE, 50% Ee, and 25% ee. Since E is dominant, the foal will have a 75% chance of being Bay and a 25% chance of being Chestnut. Now that makes a lot of sense!

Even with all of our current knowledge, and despite knowing the genotype and phenotype of both parents, it is still impossible to predict coat color 100%. That’s because spontaneous mutations, like the ones that occur on the KIT gene, can occur at any time. Coat color genetics will certainly keep you on your toes!

Genetics of disease

Learning how to identify diseases—and thus how to prevent and treat them— is the focus of most current research in equine genetics. Ever since it was discovered that HYPP was a heritable genetic disease found in Quarter Horses descended from the stallion Impressive, it has been a focus of the AQHA and its members to eliminate this disease from the population. Knowing the genetic mechanisms of other diseases can help us to selectively breed them out of horses as well. Similarly, knowing which genes are affected in a certain disease can help in developing treatments targeted at the specific proteins or pathways affected by those genes.

Did you know that there are dozens of tests available for equine genetic diseases? Did you know that most equine genetic testing only requires a sample of hair from your horse’s mane or tail? Did you know that your breed registry may offer discounts on genetic testing for its members? Well, now you do! You’re welcome.

Amongst her many research projects, Dr. Brooks is doing a study on Anhidrosis (non-sweaters) with some interesting early results. If you own a non-sweater, please consider enrolling your horse in her study. You could be a part of the first effective treatment for Anhidrosis! Call our clinic for more information on this.

That’s the extent of what I recall from Dr. Brooks’ brilliant and informative seminar, but this is only a fraction of the information she presented. In case you missed it, head on over to my YouTube channel where you can re-play the live video. Also, check out my next See-Tony event, the Deworming Seminar to be held here on March 8th at 6:30 pm!

Until next week,


Tuesdays with Tony is the official blog of Tony the Office Cat at Springhill Equine Veterinary Clinic in Newberry, Florida. For more information, please call us at (352) 472-1620, visit our website at SpringhillEquine.com, or follow us on Facebook!

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