x chromosome
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x chromosome
why do great broodmare sires originate? i use the examples of dr fager and buckpasser---two fantastic broodmare sires---they became great in this area because they transmit their x chromosome to all of their daughters but none of their sons.
X Question
Stan,
I'm very interested in the X factor chromosone, but I guess I'm confused about this whole X factor transmission thing. I thought I had read X factor could only be passed on through females. According to your post above, I was mistaken. So a sire can inherit the X-factor from his dam and pass it on to his daughters, but he can't pass it on to his sons, right? I
am assuming then that a mare can pass on to both sexes, but a stallion can only pass to females. Do I have this right?
Thanks for educating me.
Laurie
I'm very interested in the X factor chromosone, but I guess I'm confused about this whole X factor transmission thing. I thought I had read X factor could only be passed on through females. According to your post above, I was mistaken. So a sire can inherit the X-factor from his dam and pass it on to his daughters, but he can't pass it on to his sons, right? I
am assuming then that a mare can pass on to both sexes, but a stallion can only pass to females. Do I have this right?
Thanks for educating me.
Laurie
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xfactor fan
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x chromosome
Laurie,
Here's how genetic stuff works.
Stallions are YX, Mares are XX. The Y chromosome is very small and doesn't carry all that much information. A stallion creates sperm that are either Y, or X.
The mare creates an egg that is X, contributing one or the other of her X's to the egg.
When egg and sperm meet, the resulting combinations are
Y sperm & X egg= colt
X sperm & X egg= filly
So far this is pretty straight forward. Now here comes the tricky part.
In order to function a horse (and most other animals) need only one functioning X. Too much X is a bad thing. So in the brief time between fertilization and implantation, a female embryo will have two functioning X's. This is apparently what causes the embryo to develop into a female. Around the time of implantation one of the X's turns off.
This is called X chromosome inactivation. It was once thought that this was totally random, leaving the female a mix of cells with the two X's.
The classic example of this is the Calico or Tortishell cat. In cats the colors for orange and black are on the X chromosome, so there are black male cats, and orange male cats Y(Xblack) , or Y(Xorange), but never male cats that are calico.
Females are: Xblack+Xblack=Black
Females are: Xorange+Xorange=Orange
Females are: Xblack+Xorange=Calico
If you look closely at a calico cat, they have large areas that are either black, or orange with some mixing of colors. But the overall impression is that of a spotted cat, rather than a roan animal.
Tortishell cats are mostly black with swirls of orange. Here the black X is strongly expressed, and the orange much less.
Getting back to the horses. The X-factor theory is that the genes that determine heart size are carried on the X chromosome. At some time in the past, there was a mutation that increased the heart size. This is well documented and goes back as far as Eclipse, who had a very large heart, as did Sham and Secretariat.
So the idea behind the X-factor heart gene theory is that if a stallion carries a large heart X, he will only be able to pass this on to his daughters, and not to his sons.
Because of X-chromosome inactivation, his daughters may express his large heart X, or not.
In turn, the daughters may pass the large heart on to their sons or daughters.
The broodmare sire effect may be as simple as the X factor makes it. A X factor sire passing his increased cardio on to his daughters, and then on to the next generation.
An alternate explanation may be that the best daughters of a good stallion may be kept by the breeders, they in turn are mated to good stallions, creating a broodmare sire.
Hope this answers your question.
I'd love to start more discussion on this topic.
Here's how genetic stuff works.
Stallions are YX, Mares are XX. The Y chromosome is very small and doesn't carry all that much information. A stallion creates sperm that are either Y, or X.
The mare creates an egg that is X, contributing one or the other of her X's to the egg.
When egg and sperm meet, the resulting combinations are
Y sperm & X egg= colt
X sperm & X egg= filly
So far this is pretty straight forward. Now here comes the tricky part.
In order to function a horse (and most other animals) need only one functioning X. Too much X is a bad thing. So in the brief time between fertilization and implantation, a female embryo will have two functioning X's. This is apparently what causes the embryo to develop into a female. Around the time of implantation one of the X's turns off.
This is called X chromosome inactivation. It was once thought that this was totally random, leaving the female a mix of cells with the two X's.
The classic example of this is the Calico or Tortishell cat. In cats the colors for orange and black are on the X chromosome, so there are black male cats, and orange male cats Y(Xblack) , or Y(Xorange), but never male cats that are calico.
Females are: Xblack+Xblack=Black
Females are: Xorange+Xorange=Orange
Females are: Xblack+Xorange=Calico
If you look closely at a calico cat, they have large areas that are either black, or orange with some mixing of colors. But the overall impression is that of a spotted cat, rather than a roan animal.
Tortishell cats are mostly black with swirls of orange. Here the black X is strongly expressed, and the orange much less.
Getting back to the horses. The X-factor theory is that the genes that determine heart size are carried on the X chromosome. At some time in the past, there was a mutation that increased the heart size. This is well documented and goes back as far as Eclipse, who had a very large heart, as did Sham and Secretariat.
So the idea behind the X-factor heart gene theory is that if a stallion carries a large heart X, he will only be able to pass this on to his daughters, and not to his sons.
Because of X-chromosome inactivation, his daughters may express his large heart X, or not.
In turn, the daughters may pass the large heart on to their sons or daughters.
The broodmare sire effect may be as simple as the X factor makes it. A X factor sire passing his increased cardio on to his daughters, and then on to the next generation.
An alternate explanation may be that the best daughters of a good stallion may be kept by the breeders, they in turn are mated to good stallions, creating a broodmare sire.
Hope this answers your question.
I'd love to start more discussion on this topic.
xfactor fan: your description is accurate. another idea we could bring up is the power of genes other than the big heart gene which are also carried on the x chromosome. these genes also go a long way in forming superior offspring. i did a study of derby winners over the last 20 years and found that the most frequent stallions appearing in the x passing position of these winners were war admiral and mahmoud. smarty jones, funny cide and war emblem each have war admiral in the x passing position. also with the war admiral factor are--real quiet, silver charm, sea hero, unbridled, alysheba, affirmed and seattle slew. mahmoud appears in the x passing position of recent derby winners--monarchos, fusaichi pegasus, and charismatic, grindstone, pleasant colony, etc etc.
the x chromosome is a powerful thread--you need it to survive--xo horses suvive but yo horses do not develop at all--the x is vital--the y is not. however to form a male horse the y is necessary.
the x chromosome is a powerful thread--you need it to survive--xo horses suvive but yo horses do not develop at all--the x is vital--the y is not. however to form a male horse the y is necessary.
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xfactor fan
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x chromosome
<http://mmbr.asm.org/cgi/content/full/62/2/362>
This link leads to a technical paper on X chromosome inactivation. One of the many interesting things buried in the gene speak is that X chromosome inactivation is not random. Some X's get turned off more than others, which may go a long way to explaining some of the qirks of TB breeding.
Have you looked into the ideas in the second X factor book?
To recap, the idea is that the expressed X controls the development of the forehand of the horse. From the ears back to about the knees. This may also determine the height of the horse. Seems to work with + or - 2 inches.
If this is true, this should be easy to test, and should work on any breed of horse, large heart or not.
Pick any mare with several male offspring. The females are a bit tricky so they are going to be left out right now.
The mare will determine which X her colts gets, so independent of color, or sire she should throw two types of colts.
The mare will have one X that comes from her sire. The other X will come from some other ancestor on the female side of the family.
Colts getting the broodmare sire X should be similar to her broodmare sire, same forehand, and about the same size.
Colts getting the other X should also look alike, but not like their siblings with the broodmare sire X.
I've spent a lot of time looking at conformation photos, and there does seem to be something to this.
Take a look at the low set neck and curly ears of:
Princequillo
Somethingroyal
Secretariat
Terlingua
Storm Cat
Forestry, by Storm Cat, has the bulk from Storm Cat, but seems to have the forehand structure from Pleasant Colony.
Kris S. out of another daughter of Princequillo, also has the low set neck and look from that X.
Anyone want to guess where Princequillo got it from?
This link leads to a technical paper on X chromosome inactivation. One of the many interesting things buried in the gene speak is that X chromosome inactivation is not random. Some X's get turned off more than others, which may go a long way to explaining some of the qirks of TB breeding.
Have you looked into the ideas in the second X factor book?
To recap, the idea is that the expressed X controls the development of the forehand of the horse. From the ears back to about the knees. This may also determine the height of the horse. Seems to work with + or - 2 inches.
If this is true, this should be easy to test, and should work on any breed of horse, large heart or not.
Pick any mare with several male offspring. The females are a bit tricky so they are going to be left out right now.
The mare will determine which X her colts gets, so independent of color, or sire she should throw two types of colts.
The mare will have one X that comes from her sire. The other X will come from some other ancestor on the female side of the family.
Colts getting the broodmare sire X should be similar to her broodmare sire, same forehand, and about the same size.
Colts getting the other X should also look alike, but not like their siblings with the broodmare sire X.
I've spent a lot of time looking at conformation photos, and there does seem to be something to this.
Take a look at the low set neck and curly ears of:
Princequillo
Somethingroyal
Secretariat
Terlingua
Storm Cat
Forestry, by Storm Cat, has the bulk from Storm Cat, but seems to have the forehand structure from Pleasant Colony.
Kris S. out of another daughter of Princequillo, also has the low set neck and look from that X.
Anyone want to guess where Princequillo got it from?
xfactor-- do you believe that based on the research so far--that the gene or genes for large heart in the horse is found on the x chromosome?
or is there a group of scientists that have not adhered to hahn's basic tenet--the x carries the large heart gene?
the princequillo heart is by far the largest. how come prinequillo only appears in 2 derby winners in the X passing position. war admiral, mahmoud and blue larkspur are the most frequently appearing stallions in derby winners in the x passing positions on the dam side over the last 25 years. even before that in the 60s and 70s ----princequillo is not found in the x passing positions of any derby winners except secretariat. how come secretariat has never gotten a derby winner fom the broodmare sire position when in fact all his daughters get his super x and they in turn pass that x on to 50% of their sons and daughters?
or is there a group of scientists that have not adhered to hahn's basic tenet--the x carries the large heart gene?
the princequillo heart is by far the largest. how come prinequillo only appears in 2 derby winners in the X passing position. war admiral, mahmoud and blue larkspur are the most frequently appearing stallions in derby winners in the x passing positions on the dam side over the last 25 years. even before that in the 60s and 70s ----princequillo is not found in the x passing positions of any derby winners except secretariat. how come secretariat has never gotten a derby winner fom the broodmare sire position when in fact all his daughters get his super x and they in turn pass that x on to 50% of their sons and daughters?
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xfactor fan
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x chromosome
The example of the Princequillo line was just an example. The low thick neck makes it a very easy marker to spot.
In terms of racing success, the War Admiral --Domino heart line is the most successful.
As for why the Secretariat line hasn't had the success? Perhaps they tend toward big horses that mature late, which would count against them in the early three year old races.
As for heart genes. My best guess is that there is a section on the X chromosome that governs heart size.
In terms of racing success, the War Admiral --Domino heart line is the most successful.
As for why the Secretariat line hasn't had the success? Perhaps they tend toward big horses that mature late, which would count against them in the early three year old races.
As for heart genes. My best guess is that there is a section on the X chromosome that governs heart size.
This stuff is fascinating!
OK, a couple of questions. Is the X Factor option on the database reliable? The broodmare sire of one of my mares is Bandwagon, a son of Secretariat. My mare very closely resembles Somethingroyal in her build and conformation (at least according to pics I've seen of Somethingroyal with the huge heartgirth and set back shoulder). On the database when I click the X factor option, it shows brown boxes and lines on the bottom side of her pedigree which seems to indicate her dam may have had X-factor potential coming through the tail-female side of her pedigree. Do you think this all adds up to a good chance my mare has X Factor or am I just clutching at straws?
Laurie
OK, a couple of questions. Is the X Factor option on the database reliable? The broodmare sire of one of my mares is Bandwagon, a son of Secretariat. My mare very closely resembles Somethingroyal in her build and conformation (at least according to pics I've seen of Somethingroyal with the huge heartgirth and set back shoulder). On the database when I click the X factor option, it shows brown boxes and lines on the bottom side of her pedigree which seems to indicate her dam may have had X-factor potential coming through the tail-female side of her pedigree. Do you think this all adds up to a good chance my mare has X Factor or am I just clutching at straws?
Laurie
So many pedigrees...so little time. (C)
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xfactor fan
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x chromosome
Bandwagon, the son of Secretariat would have Secretariat's Y, which is the same Y from Bold Ruler, and so on up the pedigree.
The X comes from the female side of the family.
Show Stopper would have the broodmare sire X--in this case Native Dancer. This is 100% sure.
The other X could come down through the female side from Raise You, daughter of Case Ace, who could carry the Domino X.
Or via Lady Glory by American Flag who was by Man O War, but could have gotten his X from the damsire ROI HERODE.
Or the Wiskbroom II X via Beloved.
If Bandwagon is a large heart stallion, his race record is proof that it takes more than a large heart to be a good racehorse. 22 starts 2 wins 4 place 3 show.
Who does Bandwagon look like?
The X comes from the female side of the family.
Show Stopper would have the broodmare sire X--in this case Native Dancer. This is 100% sure.
The other X could come down through the female side from Raise You, daughter of Case Ace, who could carry the Domino X.
Or via Lady Glory by American Flag who was by Man O War, but could have gotten his X from the damsire ROI HERODE.
Or the Wiskbroom II X via Beloved.
If Bandwagon is a large heart stallion, his race record is proof that it takes more than a large heart to be a good racehorse. 22 starts 2 wins 4 place 3 show.
Who does Bandwagon look like?
My mare's name is Glorieta. I believe she's Glorieta4 in the database, by Look See (Conquistador Cielo out of a Danzing mare) and Miss Izora (Bandwagon x Carmoline). Carmoline was a multiple SW/SP and producer of SW/SP, albeit regional stakes.
Although Bandwagon didn't perform well or sire anything of note (to the best of my knowledge) on the track, he might possibly have been used primarily as a Sporthorse sire. I know he sired a horse who was once ranked 12th in the nation in show jumping, which in my book translates to athleticism and possible large heart. But since Secretariat couldn't have passed X factor on to his son, that's a moot point.
Although Bandwagon didn't perform well or sire anything of note (to the best of my knowledge) on the track, he might possibly have been used primarily as a Sporthorse sire. I know he sired a horse who was once ranked 12th in the nation in show jumping, which in my book translates to athleticism and possible large heart. But since Secretariat couldn't have passed X factor on to his son, that's a moot point.
So many pedigrees...so little time. (C)
To x factor: Sorry, I didn't see your question the first time.
Bandwagon looked a lot like Secretariat colorwise, chestnut with the blaze. The only pic I saw of him was not a professional shot and sure didn't present him at his best. He had a pretty drastic topline (high withers with steep angle to the back that almost looks like a swayback) and was over at the knees. I don't think they could possibly have taken a worse shot and I'm sure the horse had to look better in person. His jumper son was almost a clone of him.
Glorieta is a bay with two hind socks.
Laurie
Bandwagon looked a lot like Secretariat colorwise, chestnut with the blaze. The only pic I saw of him was not a professional shot and sure didn't present him at his best. He had a pretty drastic topline (high withers with steep angle to the back that almost looks like a swayback) and was over at the knees. I don't think they could possibly have taken a worse shot and I'm sure the horse had to look better in person. His jumper son was almost a clone of him.
Glorieta is a bay with two hind socks.
Laurie
So many pedigrees...so little time. (C)
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xfactor fan
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X Question
Sort of. The large heart is a fact, established by measuring the hearts of dead race horses, and goes back to Eclipse.
Heart scores seem to follow heart size, again there is proof of this, obtained by testing horses then measuring the size of the heart after death.
What is not clear is the exact method of transmission of the heart size. Theories include the X- chromosome, some sort of autosomal chromosome, or some type of maternal/paternal influenced chromosome pattern.
Also up for debate is the exact influence the large heart has on race performance.
Are folks up to a expanded look at this question? I've got a fairly large post that I was reluctant to post because of the flaming going on.
Heart scores seem to follow heart size, again there is proof of this, obtained by testing horses then measuring the size of the heart after death.
What is not clear is the exact method of transmission of the heart size. Theories include the X- chromosome, some sort of autosomal chromosome, or some type of maternal/paternal influenced chromosome pattern.
Also up for debate is the exact influence the large heart has on race performance.
Are folks up to a expanded look at this question? I've got a fairly large post that I was reluctant to post because of the flaming going on.