What is a fitting anniversary gift for an international team of geneticists and a Thoroughbred mare called Twilight, who sacrificed a small sample of DNA to have all of her chromosomes sequenced in their entirety five years ago? Why, a second fully sequenced equine genome, of course.

A Texas A&M University research team led by Scott Dindot, PhD, an assistant professor in the Department of Veterinary Pathobiology, recently finished sequencing, or “mapping,” the genome of an 18-year-old Quarter Horse mare called Sugar.

Further, Dindot and colleagues compared Sugar’s genomic map to Twilight’s and found more than 3 million differences, called genetic variants. Many of these differences were present in genes involved in sensory perception, signal transduction (inside and between cells), and immunity.

“We also found that the mare had a different number of copies of some genes relative to Twilight, which has never been reported in horses before,” Dindot relayed. “We recently completed another study looking at these copy number variants (CNVs) to help determine what the differences in copy numbers between different horse breeds mean. For example, CNVs cause many diseases in humans, and we suspect that the same might be true in horses, but more research is needed