The genome of the domestic horse (Equus caballus) was sequenced by an international time of researchers lead by scientists at the Broad Institute of MIT and Harvard. The three-year project uncovered a genome that is comprised of roughly 2.7 billion "letters" or nucleotides. That makes it smaller than the cow and human genomes, but slightly larger than the genome of the domestic dog.
The genome analysis was carried out on the DNA from an adult female thoroughbred named Twilight. More than just a biological catalogue, this research could lead to real benefits for equine and human health. It should also be beneficial to horse breeding as scientists will possess the tools to look for the genetics of specific phenotypic traits.
The researchers found that horses share much of their DNA with humans and noted that horses suffer from more than 90 hereditary diseases that are similar to those in humans. These include inflammatory diseases and muscle disorders. The horse is a good model for human diseases, but this won't be a one-way street. Identifying the genetic culprits that cause illnesses in horses can deepen scientists' understanding of the pathogenesis of these conditions in both organisms as well as finding out how human and equine bodies respond to them.
As part of this huge endeavour the scientists also studied the DNA of a number of other horse breeds including Andalusian, Arabian, Hanoverian, Icelandic Horse and Norwegian fjord horse. They were surveying the amount and degree of genetic variation within breeds and across them. The end result of this was a catalogue of more than 1 million single nucleotide polymorphisms or SNPs (pronounced "snips"). SNPs are DNA sequence variations that occur when a single nucleotide in a sequence is altered.
So why is this SNP catalogue useful?
Single nucleotide polymorphisms are useful for finding the genetic basis of disease. They don't cause disease but they are useful indicators. A single nucleotide base change in a gene sequence can be enough to alter a protein product to make disease development more likely.
And in this domestic horse genome mapping research the scientists used the SNP catalogue to look for the candidate mutation that causes Leopard Complex. This is a condition in which horse coats have mottled patches of white and sometimes coloured spots. Horses with this trait can suffer from a form of night blindness that also affects humans. The research was able to narrow the list of genetic suspecs down to 42 SNPs, including two candidate genes residing near a gene involved in pigmentation.
The domestic horse genome will be freely available to the scientific community in the hope that it will speed up research into uncovering the genetic causes of diseases that afflict humans and horse. From this, better diagnostic tests could be developed as well as therapeutics to improve equine health and human health.