Well some arguments here are misunderstood and some are contradictory.
Saying that mating a clean cow to a carrier bull or visa versa ends up with the offspring having a 50% chance of being a carrier does not mean that if you always mated that cow to that same bull that half her offspring would be carriers and half clean. It means that each specific calf has a 50% chance, just the same as each specific calf is going to have a 50/50 chance of being boy or girl(I realise that sex determination doesnt work the same way, just using it for illustration purposes) but if you look at all of a cows calves over her lifetime they may not be half of them boys and half of them girls.
Relating the ability of clean sires to Secretariat is kind of off base as well. By stating this you are stating that this is a sex linked gene, which as far as I know it isnt. (I also wasnt aware that the size of secretariets heart was sex linked either, but I could be mistaken.) I have seen no research into if TH is a sex linked gene, yet I am going to use my intuition to say that it isnt, to explain myself I gather this by saying we can know that it isnt linked to the Y Chromosome because then it would be impossible to have a carrier cow since she doesnt have a Y Chromosome. I am also going to say that it cant be linked to the X Chromosome because then the only way for one to be homozygous(lethal) would be for that individual to be a heifer, and I dont think that is the issue.
This same sex linkage argument in my opinion contradicts the theory that carrier calves are bigger boned, hairy, stouter because these genes are all close together and they inherit them all together . By your argument that it is impossible for these clean bulls that are good to sire good steers would mean that the TH Gene and genes for all those positives would in some instances be located on different chromosomes, thus making it impossible for them to inherit them all together.
Lastly, and I sound like a broken record saying this. TH and PHA are RECESSIVE genes NOT CODOMINANT GENES at least as far as my study of the research concludes. So even if there were varrying "strengths" of the gene as some want to say, and even though there are different actual mutations that are all called TH, it doesnt matter. The ONLY possible way for a recessive gene to have any impact on the development of the individual is for that indiviual to be homozygous for that gene. If they are heterozygous for the gene then the gene has absolutely no affect whatsoever on the development of the indivudual. This includes muscle amount, bone substance, and amount of hair. If the gene were codominant then it would be possible for it to mix and match what it affects, but that would also mean that it would be possible for the lethal deffect to present itself in heterozygous individuals.
The reason that so many carrier have good hair, muscle, bone, look, etc is because the genetic lines that introduced the mutations also had those characteristics. So it was just natural for them to have both. The TH gene didnt grab hold of the other genes and bring them with it, they just happened to get both. Everyone wants to say that you can visibly pick out carriers, I say its more likely to go to shows and pick out carriers. Yes Carriers are most likely gonna have good hair, bone, etc, but there are plenty of carriers out there that dont have a lick of hair, bone, or muscle, you just never hear about them because nobody wants them regardless of their carrier status. And like was pointed out with Thriller earlier and many other animals out there like him, there are plenty of people out there that would have lost money because they would have quicly without hesitation bet money that he was a carrier based on his look.
Truth of the matter, all these arguments that you have to have these genes to have the look. Who out ther is picking their cattle based on carrier status??? I dont know any, but if you do then please let me know, because I will sell them all the phenotypically indesirable carriers I produce. Truth of the matter is we all chose our cattle, regardless of if its a steer, heifer, or bull based on physical apearance first, then we look at pedigree. The only difference is some people will not buy anything for breeding purposes that is a carrier, while some dont care if they are a carrier. However, I have yet to see anyone, regardless of their stance on the issue, that found a good one and then decided not to buy it because it was clean. That alone should negate all of their own arguments that the genes are required. We know they dont buy steers based on their carrier status because nobody tests steers, therefor a steers status is pure speculation. If you know of anybody that only buys carrier steers send them myway next year, all of my steers will be carriers if they want them to be.
Another thing , I remember a few years ago a pretty respected guy promoted this bull that was double carrier because of all this hype that one had to be a double carrier to be worth a darn. Maybe I missed something but I have yet to here of any calves out of that bull so that must not of worked for them???
