Genetic Tests For Thoroughbreds

[vineyridge]

What you want to bet the Hobby was where the CC came from?

I'd bet Barbs myself. If QH have as much Spanish Colonial horse as they are supposed to, that is definitely Barb influence.

[diomed]

What you want to bet the Hobby was where the CC came from?

I'd bet Barbs myself. If QH have as much Spanish Colonial horse as they are supposed to, that is definitely Barb influence.

Co-sign on that.

[Dave C]

As Pan Zareta has pointed out and is highlighted by Dash for Cash's close relationship to Secretariat, the racing QH is almost entirely TB. Therefore the racing QH must have recieved the 'C' allele from the TB and not another source such as the Spanish Colonial.

The question is where the TB got the allele from. Yes, I was poking a bit of fun at the Phalaris thread with the suggestion that he was responsible, but the study does not rule it out in that the stamina breeds that they sampled did not have the allele. The study does not try to answer the question of where it came from and I'm not sure that it matters since as breeders we have to work with the genes available in our horses no matter what they are or where they came from.

[vineyridge]

Ignorant question: could the alleles that have been identified come from one side only or do they come from both the sire and dam? The CC, CT, and TT combinations?

[madelyn]

vineyridge, I think each allele comes from one parent. The DNA from each side, simplistically speaking, is in a strand, and the alleles have to line up beside each other to create a complete animal. Think back to high school biology and the genetic probability tables for humans - simple things like eye color (ie two blue eyed parents cannot produce a brown eyed child).

Think, also, about the sterility of mules. The donkey and the horse are separate equine species, but the alleles line up ENOUGH to create an animal, except for the reproductive alleles, so the resulting animal is sterile and cannot reproduce (there have been some exeptions but I suspect those were mutations).

[Pan Zareta]

the stamina breeds that they sampled did not have the allele.

Yes. They did. But no C/C homozygotes were found among the 38 National Hunt horses. (National Hunt horses don't have to be TB, but that's the predominant influence. The argument could be made that they're a stamina analogue to the short-sprinting subset of TBs that we call racing QH.) Thirty-two percent of the Nat'l. Hunt samples were C/T, 68% were T/T. Of the 31 Egyptian Arabians all that's said is that >90% were T/T, ergo at least one sample had a single C allele. Breakdown on the 35 QH's, 83% (29) C/C, 14% (5) C/T, 3% (1) T/T.

It's unknown which of these alleles was first present in the species, much less within a breed or type. But we know the Thoroughbred came about b/c of 17th cent. English breeders' desire to put more 'bottom' in their stock, and they went to ME stock with a reputation for stamina to achieve that. Breeding for quarter-mile racing in North America pre-dates the establishment of the GSB by nearly a century. The point being there is plenty of circumstantial evidence of the existence of and selection for both alleles going back >~500 yrs.

Purely speculative, but I'd bet that both alleles were present in the species prior to domestication. Obviously, the horse's best defense from predation is running. C/T heterozygotes might have had an advantage in that regard, a better balance between body mass and speed for outdistancing a variety of predators.

[Pan Zareta]

vineyridge, I think each allele comes from one parent.

Correct. The SNP in question is at nucleotide position 66493737 on chromosome 18. Each parent contributes a copy of that chromosome.

[vineyridge]

I keep thinking about the new tests (over 1000 euro each) and how they will correlate to dosage.

What I really wonder is what Roberto was, since he is the most influential modern TB sire for stamina.

[Pan Zareta]

What I really wonder is what Roberto was

Obviously, the only way to know for sure would be to test him. Otherwise, look at his racing record and determine his 'best racing distance' as defined in the report. Bear in mind that he was a MGSW at 2. Compare this info w/ Figure 2 in the report. The most likely answer will be rather obvious.

[vineyridge]

My thoughts on Roberto

One would suspect that he was CT; that's the obvious answer. But if that were the case, and North American mares being what they are, you'd think that at least half of his successful get would be CC and very few TT. His reputation (and his son's reputations) for siring classic and long distance (chasers) horses would make me think that he almost had to be a TT stallion because the one thing we know for a fact is that Roberto descendants, both here and abroad, like to run long. The number of successful Roberto line sprinters is probably almost zero.

One would also suspect that North American TBs are far more homozygous for the sprint combination than European horses. And that we have almost no TT breeding stock, since we select for our kind of racing. Which would mean that over time our stock would become more and more shifted to the sprint side. I suspect that it will become more difficult to find classic distance horses because we have selected against the gene combinations that produce them.

OTOH, we will continue to run the classics, and the best of the sprinters will win. Come to think of it, that might explain the recent Breeder's Cup results for NA horses.

[Dave C]

Vineyridge, consider the hypothesis that is developing through this thread. XFF suggested that the source of the 'C' was the Hobby. PZ pointed out that the origins of the TB was in adding 'bottom' to the existing English stock (ie adding the 'T'). By implication then it is the blending of the 'C' and 'T' that is the identifying characteristic of the TB. As the breed becomes saturated with mares that are CC, stallions that are TT will rise to prominence by their ability to sire classic horses, if they are compatible with the mares in all the other myriad of genes that make up good racehorses.

[vineyridge]

As to the hobby--

IIRC, most of the mares that created the TB were also imports. Or at least Royal mares, which would imply imports. Remember that British and NA TB racing until the middle of the Nineteeth Century (and later here) were stamina events--best two of three at lengths up to 4 miles. It wasn't until at least 1830 in England and 1870 in the US that we began to select for short distance speed.

[NORTHSTAR1]

it will be interesting to see if there is a correlation between the speed/stamina indexes and the cc and tt ratings

[xfactor fan]

I suspect that anything that could run at any distance ended up contributing genetic soup that made up the TB. As for hobbies in general, there are a couple of female families that were supposed to be from Hobbie stock, and there is mtDNA in female families that is not of Middle Eastern origin, but matches mtDNA types found in "native British" breeds.

The only picture I've ever turned up of Hobbies as a breed is a line drawing, and the horses are depicted as round wide(as opposed to narrow and angular) muscular happy looking horses.

Some of this information is in the "Who's your Moma" article at the TB Heritage site.

There's also no reason the "C" gene type couldn't have come from an number of sprinting type horses. Or from horses imported by Romans for chariot racing. Until genetic testing advanced a bit more there's no way to tell for sure.

[vineyridge]

The reason I suspect Barbs carry the C is that the Godolphin Arabian is now called the Godolphin Barb. Many of the other stallions who have not survived as sirelines are described as Barbs as are many of the early mares, including the root of Family 1. That would give QHs Cs from Spanish Colonial horses as well as TBs.