It's All in the Genes: Horse Traits and Heritability

It's All in the Genes: Horse Traits and Heritability

Chestnut horses might be genetically wired to be more sensitive to environmental stimuli.

Photo: iStock

Scientists are continuing to uncover which genes are responsible for certain traits in horses

What are you drawn to in a horse? A flashy coat color? A puppy dog personality? Smooth-as-molasses gaits? Well, your dream horse didn’t come by these traits by happenstance. Many characteristics such as coat color, height, athletic ability, and behavioral tendencies are genetic in nature. And researchers are using “genomics,” the study of gene heritability, structure, and function, to determine which characteristics are connected to which genes. 

Before getting into the fun stuff, let’s break down the terminology. The genome includes all DNA that goes into an individual from sperm pairing with an egg. Every cell contains DNA in the form of chromosome pairs—except for gametes, or sex cells, which just have one chromosome. 

Each strand of chromosomal DNA is made up of organic molecules called nucleotides (guanine, cytosine, adenine, and thymine). Their sequence leads to differences in the traits the individual displays—for example, coat colors. 

Differences in the genomic DNA sequence between individual horses are called single nucleotide polymorphisms (SNPs, or “snips”). If SNPs are located near each other on a chromosome, they will likely be inherited together; this proximity enables researchers to investigate specific regions of the genome that vary in frequency between horses.

Samantha Brooks, PhD, assistant professor and founder of the University of Florida’s Brooks Equine Genetics Lab, in Gainesville, says SNPs aren’t the only reason for genome variation. Much of it is also due to sequence rearrangements or changes. “Genes that have flipped or duplicated may be responsible for variation in phenotype (observable characteristics),” she says. 

For instance, a sequence change is responsible for tobiano color (white hair on a base coat color) in pinto horses, says Brooks. While most rearrangements are benign, some are fatal, such as the overo lethal white gene responsible for a disease that suppresses intestinal activity. 

Let’s look at some of the harmless (and even desirable!) genetic variations that create horses’ unique characteristics.

Is there a genetic link between chestnuts and excitability? Are spooky horses genetically wired to spook? Is there a speed gene? This article continues in the June 2017 issue of The Horse: Your Guide To Equine Health Care. Subscribe now and get an immediate download of this issue to continue reading.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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