Buckpasser in the X

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stancaris
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Buckpasser in the X

Postby stancaris » Mon May 20, 2013 3:57 pm

Here is an interesting bit of data to support sex linked inheritence patterns.

Over the last 3 years 25% of the top 20 Broodmare sires (North American gross earnings of daughters progeny) carried Buckpasser in the X passing position.

However, in the general population there seems to be only around 10% thoroughbreds with Buckpasser in the X. Why is there such a big difference when one compares the frequency of thoroughbreds with Buckpasser in the X from the general population with that of stallions with Buckpasser n the X among the best 20 broodmare sires? It seems likely that X linked inheritence dictates or contributes to that success of Buckpasser as a great broodmare sire.

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Re: Buckpasser in the X

Postby Pan Zareta » Mon May 20, 2013 9:42 pm

stancaris wrote: It seems likely that X linked inheritence dictates or contributes to that success of Buckpasser as a great broodmare sire.

Facts indicate otherwise.

For more objective, genome-based, information about the relative importance of the equine X chromosome v. various other equine chromosomes see the first post on page 4 of 'The Mares in Great Sires' thread.

Buckpasser was a well-bred, elite, performer and undoubtedly passed many desirable traits along to his offspring. His contemporary influence is far disproportionate to his little more than 10 years in the stud and relatively small books. But those books were largely filled by the creme de la creme of broodmares active 1968-1978 and it's bordering on the ridiculous to imagine that Buckpasser's X chromosome alone might "dictate" or even be the primary contributing factor to his success as a broodmare sire.

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Postby xfactor fan » Mon May 20, 2013 11:32 pm

This is something that I put quite a bit of time into. I looks like there is a section of the X chromosome that mostly affects the forehand conformation, poll, withers heartgirth. Couldn't say anything about heart size, or function.

So if Buckpasser for example had conformation that lent it self to racing success, then it would be passed down via his daughters.

There are lots of similar forehand conformations out there, so to see the effect, start with a non-typical phenotype. Buckpasser had the "greyhound" type conformation, Deep heart girth, relatively long skinny neck, that was more tubular than wedgeshaped, and set into the chest relatively high.

If you go to the sporthorse data base, look at the racing photo of Buckpasser, then at his sire Menow, then at the Broodmare sire Bulldog. Pay particular attention to the shape of the withers. Going back another generation, look at Spearmint, then back to Thunderbolt. There's no picture of Skylark in the database.

What I found, and this is after looking at a whole lot of pedigrees, is that for the most part stallions don't pass on their forehand to their sons, (they very well may pass on the hind quarters) About half of the time the forehand is pretty clearly coming from the broodmare sire, and the rest of the time it comes from farther back on the damside.

Weekend Surprise was interesting as three of her broodmare sires had the same type of conformation. This may have contributed to her success as a broodmare--she had only the one type of forehand to contribute to her sons.

The trick in breeding racehorses may be to get all pieces to fit into a balanced individual. Sprinter type both fore and aft, or stayer but not sprinter/stayer in the same horse.

This of course is only one part of the equation--and doesn't take into consideration muscle type, cardio fitness, metabolic rates, and all the other factors that go into making a great racehorse.

If there is an X linkage, or some type of pseudo X linkage, then the numbers should work out this way in terms of forehand conformation
Sons don't look like their sires.
Half the time sons will resemble their Broodmare Sire
A quarter of the time they will resemble the Second Damsire
And the rest of the time they will resemble a more distant damsire.

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bordering on the ridiculous

Postby stancaris » Tue May 21, 2013 3:49 am

Pan Zareta: I went back and read that thread you refer to and Brogers said, "there is something going on with the X chromosome in relation to superior runners. Without a doubt. He just goes on to say its not the large heart because researchers have not found any genes (variants) located on the X that are related to heart development.

So, Brogers agrees that the X chromosome is a contributor to the development of superior runners.

Furthermore, Brogers reports that there are some variants on the X chromosome that are associated with elite runners but they are not variants in any way related to heart function or size.

I think it borders on the ridiculous to say that the X chromosome of a broodmare sire is definitely not a contributing factor to the success of that broodmare sire.

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Re: bordering on the ridiculous

Postby Pan Zareta » Tue May 21, 2013 7:26 am

stancaris wrote:Pan Zareta: I went back and read that thread you refer to and Brogers said, "there is something going on with the X chromosome in relation to superior runners. Without a doubt. He just goes on to say its not the large heart because researchers have not found any genes (variants) located on the X that are related to heart development.

So, Brogers agrees that the X chromosome is a contributor to the development of superior runners.

Furthermore, Brogers reports that there are some variants on the X chromosome that are associated with elite runners but they are not variants in any way related to heart function or size.

Brogers also said "[w]e have identified 37 SNP variants across 19 sites on the genome that separate out elite performance from non elite. The variant that reached statistical significance (P value) on the X chromosome is one of these 37 SNP's........The problem is that when you rank them for relevance, the SNP on the X chromosome is not in the top 10 as far as importance is concerned. There are significantly more important SNP's in terms of performance, that are located on other chromosomes. You are over-rating the variant on the X Chromosome." (some emphasis supplied)

stancaris wrote:I think it borders on the ridiculous to say that the X chromosome of a broodmare sire is definitely not a contributing factor to the success of that broodmare sire.

No one has said that. Please be more careful when you paraphrase the remarks of others.
Last edited by Pan Zareta on Tue May 21, 2013 8:07 am, edited 2 times in total.

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Postby DDT » Tue May 21, 2013 7:29 am

Stan

I count only 2 out of the top 20 broodmare sires that have Buckpasser as a broodmare sire, A.P. Indy and Danehill have Buckpasser as 2nd generation broodmare sire, therefore you cannot give them equal weight, so your 25% figure is actually 10%. As with any list ranking stallions by progeny earnings number of dams and number of runners plays a big part in the rankings, as does one or two high earning runners. Buckpasser sired only 313 foals and if half of them were daughters it makes his accomplishments as a broodmare sire rank up there with the best of the breed, whether his X chromosome is something special or not. As to Brogers' comments on the subject, he is one of the founders of True Nicks, therefore his opinions carry a lot of vested interest and should be considered as a little one sided.

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Postby Pan Zareta » Tue May 21, 2013 9:37 am

xfactor fan wrote:This is something that I put quite a bit of time into. I looks like there is a section of the X chromosome that mostly affects the forehand conformation, poll, withers heartgirth.


You make an excellent point about the need for conformational balance in a racehorse and interesting observations about forehand inheritance. I can think of many examples of sons whose forehand far more closely resemble a damsire's than the sire's. Can't say that this appears to me to be universally true, but I did try to look at some of the shdb photos. Never could pull up a photo there of Buckpasser's sire Tom Fool. Access to their photo bank is much easier for registered users. In the last couple of years I've tried 3x to register but never received the promised confirmatory email.

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borders on the ridiculous

Postby stancaris » Tue May 21, 2013 12:48 pm

Pan Zareta: In your post above on May 20, 2013 you said, "it borders on the ridiculous to imagine that Buckpasser's X chromosome alone might dictate or even be the primary contributing factor to his success as a broodmare sire."

What exactly is your take on this matter? Is the X chromosome a contributing factor to the success of a broodmare sire or is it no more important than any other chromosome?

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Re: borders on the ridiculous

Postby Pan Zareta » Tue May 21, 2013 4:14 pm

Stan, re-read your original post which states:
"It seems likely that X linked inheritence dictates or contributes to that success of Buckpasser as a great broodmare sire."

I gave you my take on that which you seem to have interpreted as "the X chromosome of a broodmare sire is definitely not a contributing factor to the success of that broodmare sire" even though I never made any such statement. I disputed your notion that the X chromosome "dictates" (meaning: exercise total command over) Buckpasser's success as a broodmare sire, and added that it is not even a primary (meaning: of chief importance) factor in that regard, with supporting reference to genome-based information.

Now you ask
What exactly is your take on this matter? Is the X chromosome a contributing factor to the success of a broodmare sire or is it no more important than any other chromosome?
reframing your topic as an open question rather than the declarative form in which it was first presented and addressed, and eliminating indefensible speculation that the X chromosome might "dictate" Buckpasser's success as broodmare sire.

I might ask what exactly is your take on influence of the X chromosome in regard to Buckpasser's success as a broodmare sire but the answer is pretty obvious, you're determined to overstate it.

Broodmare sire success is defined in terms of daughters' progeny earnings. Elite performers earn more. Per the information presented in 'The Mares in Great Sires' thread, there are at least 10 SNP variants on other chromosomes more relevant to elite performance than the single statistically significant variant on the X. (That information is based upon data compiled by a single company but be advised that owners and/or affiliates of other TB genetic consulting services have reported the same findings in regard to the X chromosome.)

This indicates that the X chromosome is at most a minor (meaning: of lesser importance) contributing factor to broodmare sire success and precludes the possibilities that the X "dictates" or is a primary contributing factor to broodmare sire success. The X is definitely far less important in that regard than some of the autosomes, but probably more important than others.

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Postby xfactor fan » Tue May 21, 2013 5:48 pm

See if this link to Tom Fool works.

http://www.sporthorse-data.com/d?showpi ... 1312704275

The general rule is the sires don't pass their conformation on. However if the breeder is a "type to type" sort, then the effect is masked. Or if the mare even if she doesn't look like the sire, may carry an X that throws the same type.

I actually started looking at conformation of horse crosses. Horse x Donkey, Donkey x Horse, Zebra crosses. Easy to pick out conformation. In each case the forehand conformation seems (at least to my eye) to follow the X.

Next time you run across a colt with the same conformation as the sire, check out the first couple of damsires and see if there is a match there too.

If this is what is going on, it explains a whole lot about why TB breeding is such a hit or miss proposition. A foal may have the best genes in the world, but if the package doesn't work together, they aren't going to be able to run.

And this may also be what the "Rasmussen Factor" is picking up. Inbreeding to the female side of the family, to increase the chance that the X that matches the rest of the package shows up.

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less important

Postby stancaris » Tue May 21, 2013 6:24 pm

Pan Zareta: You stated above that there are 10 SNP variants on other chromosomes more relevant to elite performance than the single variant on the X that is statistically significant.

Is it so simple that based on the above genomic studies that you can conclude that the role of the X chromosome is nothing more than a minor influence at best?

The process of genetics is much more complicated than that. Lets just agree to disagree.

DDT: Your reference to 2 of the top 20 broodmare sires having Buckpasser as a broodmare sire is not what I stated in the beginning of this thread.

Reread my first post and you will see that I said that 25% of the top 20 Broodmare sires for the last 3 years have Buckpasser in the X passing position. I never said that they had Buckpasser as their broodmare sire.

Danehill has Buckpasser as his second damsire, Unbridled has Buckpasser further back but still in the X passing position etc.

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Postby aethervox » Tue May 21, 2013 11:59 pm

xfactor fan wrote:This is something that I put quite a bit of time into. I looks like there is a section of the X chromosome that mostly affects the forehand conformation, poll, withers heartgirth. Couldn't say anything about heart size, or function.


I will go a step further and say that the entire skeleton is inherited from the dam. In her most recent book, Marianna Haun states that one of the factors that made Secretariat great was that he had five lumbar vertebra instead of six, which he inherited from the Darley Arabian through St. Simon. This gave him a longer stride. According to Haun, Eclipse has 6 lumbar vertebra, while St. Simon, Hyperion, Lexington, Phar Lap and Hanover all have 5 lumbar vertebra.

After I read this, I did some research, and discovered an article in The Journal of Heredity by H. K. Bush-Brown titled Heredity in Horses: Why the Arab Horse Has Shown Such Conspicuous Ability for Endurance in the Recent Long Distance Tests (available on Google). In the article, the author says that when breeding an Arab to a non-Arab, one only gets the five lumbar vertebra when the Arab is the dam. The author also says that while all Arabians have 1 less vertebra than other horses, some of them have one less thoracic vertebra instead of one less lumbar vertebra. He also points out that when a donkey (5 lumbar vertebra) is bred to a horse (6 lumbar vertebra), it's only when the dam is a donkey that the foal has five lumbar vertebra. He and other authors have said that the 5 lumbar vertebra is a recessive condition.

I think it's a recessive, X-linked condition, which fits the facts given in Bush-Brown's article, especially the case where a trotter's skeleton appeared with 5 lumbar vertebra, despite having no Arab ancestors in 7 generations.

I suspect that the sire has much more to do with the musculature of the foal than the dam. A good example is the "Fair Play" front end that was inherited by Man o'War; another would be the 'Bold Ruler' hindquarters, with an extra band of muscle, as described by Bull Hancock in Bill Nack's book about Secretariat.

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Postby xfactor fan » Wed May 22, 2013 1:24 am

HI Aethervox

You might want to do a bit more research on number of vertebrae. My understanding is that there is a large amount of variation in horses in general, even within even tight gene pools. Some arabs and mustangs have fewer vertebrae, some have more. Ditto with mustangs.

And just a tip, verify anything Haun states. She's a writer, and relatively weak in her understanding of science.

I think the hind end is under control of the regular autosomal patterns. Take a look at the hind end on a number of Northern Dancer sons. They all seem to have the same kind of rump. Which seems to be a very good engine for racing. Which of course may be one of the reasons for the dominance of the ND line.

The dam seems to regulate size. This whole looking into conformation started when an old time rodeo announcer started talking about horse breeding. He claimed that if you breed a TB Stallion to a Draft mare, you get a small draft horse. The reverse cross, Draft stallion X TB mare, produces a heavy TB type.

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Re: less important

Postby Pan Zareta » Wed May 22, 2013 8:12 am

stancaris wrote:Pan Zareta: You stated above that there are 10 SNP variants on other chromosomes more relevant to elite performance than the single variant on the X that is statistically significant.

Is it so simple that based on the above genomic studies that you can conclude that the role of the X chromosome is nothing more than a minor influence at best?

The process of genetics is much more complicated than that. Lets just agree to disagree.

It isn't a matter of conflicting opinions, Stan. It's a matter of fact that genome-based evidence from multiple sources indicates that other chromosomes are far more relevant to elite performance than the X.

Please note in regard to the X SNP variant discussed in the 'Mares in Great Sires' thread that there may be more than 10 more relevant SNPs elsewhere. All we were told was that the X variant is not in the top 10 of 37 SNP variants across 19 sites on the genome that separate out elite performance from non-elite.

And by academic background I'm well acquainted with just how complicated "the process of genetics" is, and in some cases is not.

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Postby Pan Zareta » Wed May 22, 2013 8:20 am

xfactor fan wrote:The dam seems to regulate size. This whole looking into conformation started when an old time rodeo announcer started talking about horse breeding. He claimed that if you breed a TB Stallion to a Draft mare, you get a small draft horse. The reverse cross, Draft stallion X TB mare, produces a heavy TB type.


If dam regulates size, wouldn't TB stallion + draft mare = large TB type and Draft stallion + TB mare = small draft type?