Genetic diversity of modern horses

Some very distinctive groupings of modern breeds emerge in this survey of modern horse breed genetic variation, and some of these groups have clear geographical associations.

Horses are very mobile, and can also be traded; much of their existing variation may also be the result of artificial breeding which might have included both selection for particular desirable traits as well as mixing different populations.

Now that there is a fairly clear picture of modern variation, it will be useful to explore how this has emerged over time. It'll be interesting to see how ancient horses fit into the modern picture: will they prove ancestral to those living in the same regions, or is there a process of continuous renewal, with multiple episodes of turnover, as good breeds emerge somewhere across the geographical range of the animal, and quickly replace less advantageous ones?

PLoS ONE 8(1): e54997. doi:10.1371/journal.pone.0054997

Genetic Diversity in the Modern Horse Illustrated from Genome-Wide SNP Data

Jessica L. Petersen et al.

Horses were domesticated from the Eurasian steppes 5,000–6,000 years ago. Since then, the use of horses for transportation, warfare, and agriculture, as well as selection for desired traits and fitness, has resulted in diverse populations distributed across the world, many of which have become or are in the process of becoming formally organized into closed, breeding populations (breeds). This report describes the use of a genome-wide set of autosomal SNPs and 814 horses from 36 breeds to provide the first detailed description of equine breed diversity. FST calculations, parsimony, and distance analysis demonstrated relationships among the breeds that largely reflect geographic origins and known breed histories. Low levels of population divergence were observed between breeds that are relatively early on in the process of breed development, and between those with high levels of within-breed diversity, whether due to large population size, ongoing outcrossing, or large within-breed phenotypic diversity. Populations with low within-breed diversity included those which have experienced population bottlenecks, have been under intense selective pressure, or are closed populations with long breed histories. These results provide new insights into the relationships among and the diversity within breeds of horses. In addition these results will facilitate future genome-wide association studies and investigations into genomic targets of selection.

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