Humans are believed to have domesticated the horse around 5,500 years ago. And the effects of domestication--including some deleterious ones--can be seen in the genomes of modern-day horses, according to a new study.

"We provide the most extensive list of gene candidates that have been favored by humans following the domestication of horses," study co-author Dr. Beth Shapiro, head of the Paleogenomics Lab at the University of California, Santa Cruz, said in a written statement. "This list is fascinating as it includes a number of genes involved in the development of muscle and bones. This probably reveals the genes that helped [in] utilizing horses for transportation."

For the study, researchers examined DNA taken from 29 horse bones unearthed in Siberia that date back 16,000 to 43,000 years, Reuters reported. Then the researchers compared that DNA to DNA from five breeds of modern domesticated horse.

The analysis identified 125 separate genes that are believed to have played a key role in the domestication process.

For instance, "we identify genes controlling animal behavior and the response to fear," study co-author Dr. Ludovic Orlando, associate professor in the Center for GeoGenetics at the University of Copenhagen in Denmark, said in the statement. "These genes could have been the key for turning wild animals into more docile domesticated forms."

But the analysis suggested that domestication also can result in certain health problems, including "genetic diseases and health risks related with metabolism, development, behavior and immune systems," study co-author Dr. Dan Chang, a postdoctoral researcher at the University of California, Santa Cruz, told The Huffington Post. "Famous examples are the lethal white syndrome, grey horse melanoma, and lavender foal syndrome that are associated with selective breeding for beautiful coat colors. We did not list specific disease-causing mutations in our paper--instead, we detected a general pattern that domestication leads to increased levels of inbreeding and accumulation of excessive deleterious mutations in modern horses."