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Kuhaylan Heify
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Dear Dr. Deb.. I ran across a study of inbreeding in Germany of a closed herd of arabs. The study showed a ,' mean herd homozygosity,' of 52.33%.. Does anything over 50% mean that a given individual is more than a direct daughter or son of a given parent? Also, if 36 horses bred over a period of 35 years each carry over 52 percent of the same genes is a breeder not in effect breeding all brothers and sisters with each other- thus doing direct incestuous breeding. So it would appear that rotating outcrosses of breeding groups within a breed or crossbreeding would be the way to go..
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Bruce Peek

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Yes, Bruce, that is what is going on. And yes, outcrossing at periodic intervals is absolutely necessary to prevent 'genetic load,' i.e. the buildup or rise in frequency in the population of very deleterious alleles. Such things as hydrocephalus, twisted snout syndrome, problems with nondevelopment of pelage, and a wide array of metabolic problems are what I mean.

Did you read the Quarter Horse articles in the horse breeding series in EQUUS Magazine? Those were in last year's issues and there the topic is discussed very thoroughly, particularly with reference to the Kleberg/King Ranch QH breeding program. You don't have to be interested in QH's to read this -- the principles discussed there apply everywhere, to all mammals and certainly to all breeds of horses -- Cheers -- Dr. Deb

Kuhaylan Heify
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Yes Dr. Deb I have your Equus quarter horse series as it is a handy reference guide. Also I ran across a couple of PBS videos on line in which domestication is discussed which mention that the Botai people are thought to have been the first ones to domesticate horses and that the Pzrezalsky( sp) were the first horses to be tamed and then after the Botais disappeared, reverted to wild status in central asia. Also they say that the horse genome essentially collapsed at about the time of domestication
and that the Y chromosome once came in a bunch of variants but was thought to have dwindled down to just one which resulted in researchers thinking that there is now only one Y chromosome spread species wide. However other studies abstracts I have looked at emphatically state that they can tell the difference nowadays between Iberian Ys, Thoroughbred Ys, and Arab Ys. The studies also state that they were able to determine that there has been recent outcrossing in track racing Arabs to Thoroughbreds, because they found the Byerly Turk Y in samples of several Arab Track
racers.
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Bruce Peek

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Bruce, this is all very interesting, but what was your actual question?

Kuhaylan Heify
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ok, Is it really true that there is only one Y chromosome? And or, has enough genomic decoding been done so that scientists can really tell the difference between Iberian, Thoroughbred, and Arab Ys?.. As I understand it most Warmblood breeds have Thoroughbred Ys. Do you know if that is the case, or if the Warmbloods have remnant native ,' Mossback y chromosomes?
The one Y chromosome theory would dovetail with the idea that there has been a massive collapse in genetic diversity among horses as a species and that the single extant Y lent itself to trainability..Also is it true that the first people to domesticate horses the Botai disappeared without a trace, save for a couple percent genetic contribution to neighboring peoples. If so why did they disappear what was the cause, Could it have been plague? It is known that sucessor peoples did suffer from plague so maybe pasturella pestis wiped out the Botais as they were an early people and might not have had time to work out folkways needed to minimise contact with ground dwelling rodents thought to be the vector species for plague..
Finally should breeders make multi generational efforts to as radically as possible outcross what ever breeds they have to reshuffle their genetic cards?
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Bruce Peek

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Bruce, you are asking me to criticize literature which has already been professionally vetted. The process of publishing scientific results involves a review process which is called "jurying", and all professional journals are not merely edited, but also juried. For example, I and my colleague Bob Timm at K.U. currently have a paper submitted to the professional journal "Archaeofauna" which is at the moment -- as the first step in the publishing process -- out for review by a "blind" panel of three reviewers chosen by the editor. It is "blind" because the authors do not get to know who the reviewers who constitute the "jury" are. They are selected by the editor because he knows them to be highly qualified peers working in the same area of expertise.

So what you are asking me to do is verify what has already been verified. If you read about the Botai people in a newspaper or in a popular magazine like "Psychology Today" or "Smithsonian", you were reading an article prepared by a reporter who had read the original report published in a professional, juried journal. For the content not to be true, then, either the reporter got his facts wrong, or else the original jury was wrong.

But neither you nor I are in any position to criticize the jury, are we. So I take the reports about the Botai people to be true and accurate, until I see a report in a juried journal which presents contrary arguments.

I am in possession of the original, juried and professionally published reports concerning the Botai. However, I am not at all familiar with what you are saying about 'Y' chromosomes, so I have to ask you to provide me with either .pdf copies of the professional literature -- or else the popular newspaper or magazine article that you read. It is normal for the reporter to cite the professional reports that he read in order to prepare his piece and those citations will appear either in the text of the popular article, or compiled at the end. I say this for your benefit, because if you're interested to that degree, you can then search Google Scholar to see whether you can obtain the original, professionally juried reports. But I repeat, you will have to send me either .pdf's of the relevant articles or else at least provide me with the citations so that I can get them myself.

As to plague and all that, Bruce, that's pure speculation on your part and I am, again, in no position to comment. -- Dr. Deb




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