Byerley Turk sire line

[Beard of Stars]

Beard of Stars

Any pedigree expert that thinks that genes originating from the Byerley Turk other than those carried on the Y chromosome have some how managed to survive 25 bouts of recombination and the fact that only 50% of a sire's genetic makeup is forwarded onward with each mating is absurd to say the least.

DDT

Hi, nice to meet you. I'm a newbie on the board but a long time user of the site.

I'm making efforts to understand more about genetics but often find the things that are said here flying right by me. I read what can, usually online, and am picking up some of the ideas and vocab.

If I can extrapolate from your above statement you are saying that whether or not the Byerley Turk line continues through its male descendants is unimportant as his heirs are not so genetically different from the rest of the thoroughbred population after hundreds of years of genetic pairings. Is that about right?

[DDT]

Beard of Stars

No, what I am saying is that it is absurd to think that any viable BT genes, except for those carried on the Y would be present in recent generations, the genetic content of every horse is different except in the case of identical twins, the point I am trying to make is that all of his male and female descendents are genetically different and that over time his influence fades out until it is not a factor.

DDT

[xfactor fan]

Welcome,


You pretty much got it.

What we're talking about is genetic reconbination. Which happens in paired chromsomes. The sex chromosomes Y and X only undergo recombination when two X's are present. When there is an X and a Y, both replicate themselves. In practical terms, this means that a sire passes on the exact Y that he got from his sire to all his colts. And all his daughters will have the same X, which is a combination of the two X's that his dam passed on.

So two stallions that are full brothers will pass on identical Y's, but will have a different combination of their dam's X.

In visual terms, if the dam had one Blue X, and one Red X, each time brother will have a recombined X that is a different shade of purple.

Research is finding that the equine Y is pretty much identical in all breeds of horses. it is also the smallest chromosome and carries information that tips the sex of the embryo from female to male, but not much else.

[aethervox]

Research is finding that the equine Y is pretty much identical in all breeds of horses. it is also the smallest chromosome and carries information that tips the sex of the embryo from female to male, but not much else.

There is one area of the horse Y gene that differs from other mammals that have been researched. This article: http://www.ncbi.nlm.nih.gov/pubmed/18544933/ says that horses have a 200kb region in the pseudoautosomal region [PAR] (the area that is shared by X and Y chromosomes) that is duplicated in the male specific region of the Y chromosome [MSY]. Since the PAR does undergo recombination, I wonder how similarities or differences in the two regions would affect the individual horse. It also means that a male horse could have more functional genes (if the area is a gene) compared to a mare due to X-chromosome inactivation.

I would also like to point out that while the Y chromosome has been mapped in horses, not all of the genes have been documented. There's a pretty good idea of what the genes do, because of similarities between horse, mouse and man, but there are always differences, and a difference in one base-pair can make a huge difference in the protein produced by a gene.

[DDT]

aethervox

While this could be true, the Y has not been found to carry any genes going to performance, and certainly the success of fillies and mares, who do not have a Y, tends to prove this fact. While the Y does give a slight advantage in size and strength development associated with the sex bias in most mammals, it has not been proved to provide any additional advantage to horses. I suggest that under no circumstance could the Y chromosome in male horses contain more genes than the activated X in female horses and that you are misreading the information.

DDT

[DDT]

aethervox

This article deals with meiosis in the male during creation of sperm cells, and while it is believed that some recombination takes place between the Y and the X, it is slight and at specific locations. Under that circumstance there could be differences in the Y, how much of a difference and the specific genes involved could certainly be important, but the fact remains that having a Y chromosome is not necessary for superior performance.

DDT

[vineyridge]

Given the current state of genetic knowledge, I do wish you guys wouldn't be so positive in your assertions. If you'd just qualify your statements with "as far as we know today", you wouldn't make it sound as if you believed people were idiots who might not agree with what you believe to be the "truth."

It's entirely possible to build a whole scientific edifice on an insufficient foundation and has been done many times in the past.

[DDT]

viney

You are correct and I apologize for any post that indicates people are idiots if they do not share an opinion. That being said, current knowledge of sexual reproduction in mammals, to my knowledge, which is limited, I am not and do not claim to be a genetic expert, has been proven to have at least two paths for creating diversity, recombination and the fact that normal sperm and egg cells contain only half of the sire's and the dam's DNA. In my opinion, this makes it highly unlikely DNA coming from the distant past could be present in the first generation.

DDT

[xfactor fan]

If there is a segement of the Y that does recombine, the question to ask is there variation in the region that recombines?

To use Donna's stallion Guaranteed Gold. He's a cremello, chestnut so he carries two copies of the red gene (e) and two copies of the cream gene CR. In genetic shorthand he's ee CRCR. No matter how many times the chromosomes recombine, he's always going to pass on e, CR.

If the segment of Y that recombines has the genes ABCD, and the region on the X is also ABCD, then, yes recombination can happen, but there is no net change.

Just something else to consider.

[pedigreeann]

Many people are misled by the Galton formulation - an individual gets half of its genes from each parent, hence a quarter of his genes from each grandparent, etc. until the the number of genes from one ancestor in the 10 generation is 1/(1024). However...., those 1024 ancestors in the 10th generation were NOT separate, distinct individuals, because the number of possible ancestors has always been limited. If one stallion occurs 25 times in that 10th generation, he has a much greater likelihood of getting his genes through. (It happens - Seattle Slew has 26 crosses of Domino in the 10th or nearer generations.)

But gene inheritance is not the same as the inheritance of TRAITS. Some traits are dominant and some are recessive and some in between. And sometimes we can actually trace traits to their source; the greying gene is an example of this.

A horse cannot be grey unless one of its parents has the greying gene. Greys nearly died out in the TB breed because of a prejudice against them during the 19th Century. All TBs who are greys today trace back to one horse, Master Robert (1817), the only grey son of the grey mare Spinster (1805). Spinster's second dam Bab was the daughter of two grey horses; the grey gene she passed down must have come from either the Brownlow Turk or the Alcock Arabian, the sources of the greying genes in her parents. Hence we can trace the greying gene of Hansen directly back 22 generations to Master Robert, and a dozen or so more back to one of two foundation sires. This is the only way Hansen could be both a grey and a TB.

Most traits are not as obvious as the greying gene, clearly. Traits associated with performance are hidden from our view until we see them on the track, and sometimes not even then, due to unfortunate circumstances. But because most stud books are to some extent closed, the majority of the traits we see in modern TBs must have come from those couple dozen foundation sires and sixty or so foundation mares. We have concentrated and shuffled those traits about, discarding the failures, but the genes that produced them have to have come from the foundation stock. Where else could they have come from? Magic fairy dust?

[DDT]

It is possible for genes from foundation stock to be present in modern horses, I do not believe it is impossible just highly unlikely. With each generation genetic content is cut in half until you reach a point where there is little or no representation. This is all Magic fairy dust?

DDT

[pedigreeann]

DDT - You still don't get it, do you? Where would any new genes come from? No other ancestors are allowed if the horse is to be accepted in the stud book. Some mutations of those genes may be present today, but those are mutations of the genes of that set of ancestors. If a gene didn't exist in the foundation stock, I don't see how it can be present in modern horses.

If you wanted to say whether this particular gene came through the occurrence of this particular horse at this one position in the pedigree, that has a very low probability. But given the thousands of times that those foundation horses appear in the pedigrees of current TBs, the likelihood that some genes of each one making it through are much higher.

Consider: the great stallion Stockwell, 'The Emperor of Stallions', who traces to the Godolphin Arab/Barb 171 times, amounting for 14.13% of his ancestry. (This figure is the result of my own researches.) This is equivalent to more than any one of Stockwell's great-grandparents (1/8=12.5%). You want me to believe that it is unlikely that Stockwell carried any genes from the Godolphin?

All of the genes of all the foundation animals are not necessarily present in all of today's TBs, and some genes have undoubtedly been eliminated from the breed, like dun and spotted colorings. But all of the genes in modern TBs must have come from the foundation stock via some route or another. There are no other genes available.

[DDT]

I do agree with you that all of the genes in the pool come from foundation stock, which branch, what exact source or path is my problem. If Seattle Slew had many appearances of Domino in his pedigree it does not mean that he carried more Domino genes than horses that have less exposure to Domino, logically it does, but Mother Nature still controls that. process.
DDT

[pedigreeann]

Okay, you are getting it. All we humans can do is increase the odds that a particular ancestor's genes are available by loading up on as many presences of that ancestor as one can.

However since we have not been assigning mates by random chance but by selection, based on traits like speed, stamina, quality and conformation, for three centuries, my guess is that the genes we wanted were possessed by the horses whose names we see most often in multiples in the ancestry. People used their stock because they transmitted the desired traits more reliably than others did.

Marcel Boussac was one who 'loaded the dice' without hesitation. He made certain that Coronation had as big a shot of getting Tourbillon's genes as possible by breeding Tourbillion's son Djebel to Tourbillon's daughter Esmeralda - must have worked, because Coronation won the Arc.

[Pan Zareta]

Another flaw of the Galton formulation is that it doesn't account for the vagaries of recombination. It assumes the genetic contribution of an ancestor is halved each generation but for generations 2 and beyond that doesn't hold true. The expected contribution from any one of the 4 'grandparents' is 15-35%, but their potential contribution is actually 0-50%.