Horse genome reveals evolutionary surprises

The Human Genome Project was just the beginning. Since its start in 1990, several other Genome Projects have gotten under way, including the Horse Genome Project, which kicked off in 1995.

Now, after 14 years of endeavour, the first complete genome of a domestic horse has been published today in the journal Science.

The international team of researchers, led by Professor Claire Wade, Chair of Animal Genetics and Computational Biology at The University of Sydney, found that the horse genome is larger than the dog genome but smaller than the human and cow genomes. However, the size of the genome is not necessarily linked to complexity, as demonstrated by the relatively large coral genome.

In comparing the horse and human chromosomes, the researchers discovered that 17 out of 32 - or 53 per cent of - horse chromosome pairs are composed of material from a single human chromosome, while only 29 per cent of dog chromosomes are composed of material from a single human chromosome.

This indicates that fewer chromosome rearrangements separate humans from horses than separate humans from dogs. The researchers also found that horses are more closely related to humans than to cows in evolutionary terms.

The researchers were also surprised to find on horse chromosome 11 the existence of an evolutionarily new centromere. Centromeres are key structural features of chromosomes that are necessary for the movement of chromosomes when cells divide, a function that ensures normal distribution of all genetic material to each daughter cell. The functional but evolutionarily immature centromere in the horse may provide a model to study factors responsible for how centromeres function.

The horse genome also reveals interesting clues as to the recent evolutionary past of the horse, particularly after it was domesticated by humans.

“Horses have their own special population history with important implications for how we map genetic traits in horses. They do not appear to have undergone a tight domestication bottleneck and the presence of many female ancestors in domestic horse history is evidence of this. It looks as though we basically domesticated all of the ancestral horses,” Professor Wade said.

It was also found that the Mongolian horse, which was believed to be an ancestor of the domestic horse, is just another horse breed, even though it possesses an extra chromosome.

It is hoped the horse genome might shed light on some of the 90+ diseases and hereditary conditions shared by horses and humans, including infertility, inflammatory diseases and muscle disorders.

“Better tests for genetic diseases such as disorders of the muscle, therapies for respiratory disease and allergic diseases of the horse are already being made possible through our increased understanding of equine biology,” said Professor Wade. The horse genome should also aid in horse breeding, which is a multi-billion dollar industry worldwide.

The genome was sequenced by an international team of researchers at the genome-sequencing center of The Broad Institute of MIT and Harvard.