Thursday, June 27, 2013

Genetic Basis of Gait in Icelandic Horse--Part 2

It is  interesting to discuss the gaits the horse displays in the field versus what they can do under saddle. 
For example, I almost never see Blessi tolting in the field; he trots everywhere but he can do a nice pleasure tolt under saddle.

As the Andersson et al study states, "31% of the four-gaited horses were homozygous A/A" so about 1/3 of the so-called 4-gaited horses in the study carried a homozygous A/A for the DMRT3 nonsense mutation so were gentically 5-gaited. If this weren't true, there would be a much higher percentage of
3-gaited Icelandics being bred.

Assuming that AA represents 5-gaited horses, CA represents 4-gaited horses, and CC 3-gaited, the percentages of expected offspring are as follows (my interpretation was confirmed by a recent article in Equus Magazine):

AA (5-gaited) crossed with AA (5-gaited) = 100 % 5-gaited. Since only AA horses have a flying pace, this is how I can interpolate that Blessi is 5-gaited.

AA (5-gaited) crossed with CA (4-gaited) = AC, AA, AC, AA, CA, CA, AA, AA or 50 % 5-gaited and 50% 4-gaited

CA (4-gaited) crossed with CA (4-gaited) = AA, AC, CA, CC, AA, AC, AC, AC OR 25% 5-gaited, 50% 4-gaited, 25% CC 3-gaited

CC (non-gaited) crossed with CA (4-gaited) = CC, CA, CC, CA  or 50 %4-gaited and 50% not gaited

So since responsible breeders are eliminating the 3-gaited horses from the breeding pool and knowledgeable breeders keep breeding back to 5-gaiters, the percentage of 3-gaited horses is kept low.

Caution: In my 9th grade science class, the teacher introduced genetics by talking about blue eyes (bb) and brown eyes (Bb or BB). He told us that 2-blued eyed parents could not have a brown-eyed child. I raised my hands and shared that my parents both had blue eyes (really green) and my sister had brown eyes (actually hazel). The teacher sputtered and went on to explain that eye color is actually determined by multiple genes and the text book was simplifying the matter. Of course, I took the text book home and told my sister she was adopted.

Also this study adds additional credibility to BLUP, which predicts which characteristics will be passed on to offspring. For example, Blessi's BLUP predicts that, assuming he was still a stallion, he would pass on the ability to pace, which I never understand since he was a "4-gaited" horse. Now that I know a bit more about the genetics, I can understand why BLUP would make this prediction.

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