X-factor question

[GoForRags]

Hi everyone-

I have a basic grasp of the x-factor theories. I do have a pretty solid science background from college, so I understand genetic expression.

I was looking at my 2-year old filly's pedigree via selection of "highlight x chromosome" and also by selecting the x-factor drop down.
The highlighting darkens some of the males in her pedigree and I wonder whether a male has to carry HH or hh or Hh in order to pass it on and how to figure out whether he does?
Looking at her pedigree, I get the impression that she carries a double allele, is that correct?
http://www.pedigreequery.com/remiel2

Her sire belongs to me, as well. Her dam passed away when Rem was 3 1/2 months old from an apparent heart attack, if that makes any difference.

Any input is appreciated )

Tres

[xfactor fan]

The theory is that the large heart is carried on the equine X chromosome. Females are XX, males XY. So whatever is on the X that the stallion carries is expressed.


So the theory is that a large heart stallion will pass his large heart X to his daughters, and his Y to his sons. So only the daughters have the potential of expressing the large heart. Adding complications to this is the process of X chromosome inactivation, where one of the two female chromosomes turns off.

Rather than using HH, or hh, it might be easier to thing about if you use X as large heart and x as normal heart. So a stallion could be XY, or xY, while a mare could be XX, Xx, or xx. with the Xx mares being genetic mosaic, and expressing a range of heart sizes from normal to large.

Hope this helps.

[Pan Zareta]

Hi everyone-

I have a basic grasp of the x-factor theories. I do have a pretty solid science background from college, so I understand genetic expression.

I was looking at my 2-year old filly's pedigree via selection of "highlight x chromosome" and also by selecting the x-factor drop down.
The highlighting darkens some of the males in her pedigree and I wonder whether a male has to carry HH or hh or Hh in order to pass it on and how to figure out whether he does?
Looking at her pedigree, I get the impression that she carries a double allele, is that correct?
http://www.pedigreequery.com/remiel2

Her sire belongs to me, as well. Her dam passed away when Rem was 3 1/2 months old from an apparent heart attack, if that makes any difference.

Any input is appreciated )

The 'highlight x chromosome function' simply darkens the entries of all names in an individual's pedigree that can contribute to its X chromosome. Males have a single X chromosome so would be expressed in single allele terms, i.e. H or h, but in regard to heart size this is a moot point. The hypothesis of a single gene on the X chromosome that controls heart size was unrealistically simplistic if not completely implausible when first published 15 years ago. Since then, however, the equine genome has been mapped. No candidate gene for control of heart size was identified on the X but one or more have turned up on other chromosomes.

The only reliable way to determine Remiel's cardiovascular capacity is to have it measured. It's a shame that she was so young when she lost her dam. Good luck to her and you.

[GoForRags]

Thanks both of you. I wondered if in theory, following the chromosome on the X would be so logically easy, why it shouldn't be more widespread practice to simply be able to know by researching a horse's pedigree.

I appreciate your explanations. I think I'll just let Rem surprise me once I start training her LOL. Her sire has quite the chest and lungs and while bred for speed, has a ton of stamina.
Hard to gauge at this point where her talent with fall but by being simply wonderfully correct and well-put-together, part of the battle won't be as tough.

Does anyone actually breed for the large heart purposefully?
I somehow always saw Secretariat as a lucky one. Would be nice if we could determine heart size simply by matching the right kinds of pedigrees.

[stancaris]

Go For Rags: I for one believe that the X chromosome is very important in establishing leading broodmare sires like Buckpasser, Deputy Minister, etc.

Since the X is transmitted by a sire to all his daughters and none of this sons it is this X that marks the spot for developing great broodmare sires. On the X are probably very important genes that all daughters get and they in turn transmit a certain percentage of that X chromosome from their father to all their duaghters and sons.

Even if its not the heart itself that is a result of gene action on the X chromosome the importance of the X is still strong. It could be bone development or spleen development or lung development or a whole myriad of characteristics that reside on the X and go a long way in establishing the great broodmare sires of all time.

X linked inheritence is certainly a contributing factor in establishing Buckpasser as one of the greatest broodmare sires of all time. He led the list of broodmare sires in 4 different years.

[xfactor fan]

I'm pretty convinced that forehand conformation Poll-Neck-Withers-Ribs-Shoulder is linked, and on the X. Hind quarters are controlled somewhere else.

The trick in breeding may be to match the correct body parts so a balanced horse is created.

I started noticing this several years ago, then started paying attention, then actually started finding conformation pictures, and it does seem to be true. And the numbers seem to be in line with the this theory.

[Pan Zareta]

X linked inheritence is certainly a contributing factor in establishing Buckpasser as one of the greatest broodmare sires of all time. He led the list of broodmare sires in 4 different years.

Remember that in previous pq forum discussions of the X factor and X chromosome it's been reported that full genomic analyses indicate the X is not as important as some of the autosomes (chromosomes other than the X and Y) in regard to predicting elite performance and that non-Mendelian modes of gene control and expression may mimic X-linked inheritance. Buckpasser's book included some of the best performing and producing mares of his time. No argument that he was one of the greatest broodmare sires of all time, but it would be remiss not to attribute at least some small share of that success to his consorts.

[stancaris]

Pan Zareta: You said, "non-Mendelian modes of gene control may mimic X linked inheritance."

What exactly does that mean? Could you give an example?

[CosMos]

http://en.wikipedia.org/wiki/Genomic_imprinting

http://learn.genetics.utah.edu/content/epigenetics/imprinting/

[Pan Zareta]

Thanks CosMos!

[CosMos]

no prob...