by Neil D’Cruze
Single mutation keeps racehorses in the money
[Via Ars Technica]
When Darwin was building the case for his Origin of Species, he frequently relied on breeding of domestic animals as an example. If people could create so many varieties by selectively breeding naturally occurring variations, just imagine what natural selection could do over deep time, he argued. Now, researchers have identified a single mutation that changes the way horses can manage their gait, or the timing and pattern of their leg movements. Although the mutation shows up in a number of breeds, it’s present in a very high number of harness-racing trotters—where its presence was linked to increased winnings.
Horses are noted for having a variety of very distinct gaits, ranging from ambling and trotting, up to a gallop. Each of these comes with distinct rhythm of leg movements, placement of footfalls, and patterns of fore- and hind-limb motions. As horses have been bred for everything from heavy lifting to showing off in flashy parades, different gaits have become predominant in specific breeds. The new work, published in Nature, simply scans the genome for genetic differences associated with the use of a specific gait, called tölt, that is common in Icelandic horses, which have been isolated from their European ancestors for centuries.
The genome scan ended up indicating that, rather than being a complex trait, the ability to use this gait was associated with a single, well-defined area of the genome. And, when they sequenced this area of the genome, they found an equally well-defined change: a single DNA base that lops the end of the protein produced by a gene called DMRT3.
The mutation adds a stop codon, removing the last couple of hundred amino acids from the end of the protein.The protein makes a trasncription factor, responsible for controlling the production of many, many proteins.
So one change can have a large effect on many other genes. IN this case, it appears to be involved with nerve transmission affecting left-right limb movement.
And, because horses have been breed for such a long time, we can look to see where this mutation has popped up. Turns out it is very common in horses requiring high speed at a specific gait, such as trotting. All American trotters have two copies of this mutation.
When testing horses with the mutation versus those without, the researchers were able to demonstrate that those horse with the mutated transcription factor were able to maintain their trot at a higher speed for longer. And it is not found at all in horses whose breeding is not determined by gait (a p(A) vale of 1 means all the horses had the gene on both chromosomal copies, 0 means they had no copies and 0.5 means that it is found on onlu 1 copy.,:
Here is an example of an Icelandic horse and the tölt: