The evolutionary history of the DMRT3 ‘Gait keeper’ haplotype.

This research article discusses a study aimed at determining the evolutionary history of the DMRT3 ‘Gait keeper’ mutation in horses, which is known to influence alternate gaits and performance in harness racing. The study utilized sequences from a variety of horse breeds to identify sequence polymorphisms associated with the mutation, concluding that the mutation likely occurred just before or after domestication and then spread globally due to selection on locomotion traits.

Study Purpose and Aim

• This study seeks to determine the origin of the DMRT3:Ser301STOP mutation, often colloquially called the ‘Gait keeper’ mutation, in horses. This mutation is associated with unique gait patterns and improved performance in harness racing.
• The aim of the study is to ascertain when and where this mutation first appeared, to identify any other potential cause-and-effect mutations, and to calculate the coalescence time for present-day haplotypes carrying this mutation.

Methodology

• The researchers used sequences from 89 horses across 26 breeds. The purpose was to identify ‘Single Nucleotide Polymorphisms’ (SNPs) in the DMRT3 gene – these are variations at a single position in a DNA sequence – that are in strong linkage disequilibrium with the Gaits keeper mutation. Linkage disequilibrium refers to a situation where the combination of alleles (variations of a gene) observed at two different locations in the genome occurs more or less often than would be expected by random chance.
• They then genotyped these 102 SNPs in an additional 382 horses (from 72 breeds) and identified 14 unique haplotypes. A haplotype is a set of DNA variations, or polymorphisms, that tend to be inherited together.

Findings and Conclusions

• The study concludes that the DMRT3:Ser301STOP mutation is, without doubt, causal as no other sequence polymorphisms have shown such a strong association with traits related to horse locomotion.
• The researchers found that the sequence diversity among mutation-carrying chromosomes was low, indicating that they must have diverged from a common ancestral sequence within the last 10,000 years.
• Therefore, it was concluded that the mutation likely occurred just before horse domestication or sometime after, and then spread throughout the global horse population due to selection pressure on locomotion traits. This suggests that the gait pattern associated with this mutation was beneficial and favored in breeding programs, leading to its widespread adoption in various horse breeds.