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 Heterosis Needs a Homozygous Recharge

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Kent Powell



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PostSubject: Heterosis Needs a Homozygous Recharge   Mon Mar 12, 2012 12:40 pm

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larkota



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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Mon Mar 12, 2012 1:21 pm

had this ripped out as something to read from time to time.

"Even the longest journey must begin where you stand."
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MKeeney
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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Mon Mar 12, 2012 1:37 pm

thx Kent...Jim Lents, a thinker and writer extraordinaire...

For the past three-plus decades our industry has been in decline. We've suffered the same fate other mature industries have suffered; that is, loss of market share, quality in decline and loss of ultimate consumer acceptance. Industries in this condition are ripe for a revolution, and I believe the beef industry is positioned for just such a revolution.

When it happens things will be different. The rules of the game will be permanently changed. Unless there is serious change in the beef breeds and their associations, breeds will become even more irrelevant than they are today and will lose value. Well-selected linebred genepools will increase in both importance and value. The commercial sector no doubt will still seek heterosis, but hopefully learn that all F-1 animals are for market purposes, not breeding purposes. When revolution comes to our industry, it isn't likely to be led by current industry leaders blinded by status quo thinking. It will be the work of the next generation, many from outside the industry, joined by a handful of visionaries from the present generation.


who among us will step up and invest {mostly time} in a new beef industry
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G nome



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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Tue Mar 13, 2012 12:21 pm

Interesting and for the most part I agree with the author. However, one statement in the article about heterosis not being and answer for within breed differences if the breed had been kept pure needs some explanation beyond the article.
The process is assortment and action of genes. Expression of combinations of genes aligned with other alleles is favorable to phenotype so that it can be measured. The question should be: does the largest, fastest gaining, or heaviest milking animal compared with contemporaries within a breed achieve this by homozygous favorable genes or accumulation of multiple heterozygous pairings along the two respective strands of DNA? The process is a continuum of genetic combinations, the breeds are recongizable traits known to be homozygous and heritable within the breed, but everyone knows these animals are not 100% homozgous in DNA profiles.
Heterosis should be measured above the median parent, but commonly is only measured against smaller of the two (often these are breed averages as well).
Line breeding or outcrossing, in order to be a successful program, must rely on selection for solid benefit.
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MKeeney
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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Tue Mar 13, 2012 1:31 pm

G nome wrote:
Interesting and for the most part I agree with the author. However, one statement in the article about heterosis not being and answer for within breed differences if the breed had been kept pure needs some explanation beyond the article.
The process is assortment and action of genes. Expression of combinations of genes aligned with other alleles is favorable to phenotype so that it can be measured. The question should be: does the largest, fastest gaining, or heaviest milking animal compared with contemporaries within a breed achieve this by homozygous favorable genes or accumulation of multiple heterozygous pairings along the two respective strands of DNA? The process is a continuum of genetic combinations, the breeds are recongizable traits known to be homozygous and heritable within the breed, but everyone knows these animals are not 100% homozgous in DNA profiles.
Heterosis should be measured above the median parent, but commonly is only measured against smaller of the two (often these are breed averages as well).
Line breeding or outcrossing, in order to be a successful program, must rely on selection for solid benefit.
EG,
would you apply the same selection principles to inbreds that you would not closely related type to type matings? for example, if yearling weight was the goal {line one etc}, select the high individual? what if optimization {consistent type}of a cowherd was the goal?
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G nome



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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Tue Mar 13, 2012 6:35 pm

Though it seems odd, we generally get what we select for. If we select for larger than average, we get larger than average because there is some heritable portion to most any trait. If we select of optimum and it is about average of the herd now in esistence, it would seem that 100% would be the target ratio, not 115% any more than one would select for 85% of herd average. In selecting from linebreds vs. outcrosses, I would expect the same selection criterea be used, but would expect a wider range in those available from which to select the 100% replacements. It will take many more generations to reach the goal of stable predictable bell curves once the outcross has been made. If this is within breed, the time frame expected would be less than that of inter breed crosses, or for sure and for certain interspecific crosses.
Many years ago, my major professors, Harlan and DeWet, came up with the gene pool description of the process of potential hybridization and gene exchange that would result in introgression of traits of interest. There was the primary gene pool in which all offspring were viable and potentially available as parents. The secondary gene pool had some difficulty in the F1 that reduced the success rate in attempted reproduction. Tertiary gene pools resulted in sterility (ie. true interspecific crosses). The final category listed such things as fusion of nuclei, transformations, etc. The report had examples each manmade and natural. Interesting that we were working with elevated numbers of chromosomes in corn relatives, but fertile individuals eventually came around by BC 4 or 5.
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MKeeney
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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Tue Mar 13, 2012 8:20 pm

BC is not body condition score...right? Smile
I am assuming that the secondary gene pool was created from the primary gene pool ? if so, could not the primary gene pool be re-created by the crosses of the secondary gene pool?
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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Tue Mar 13, 2012 9:19 pm

What is the heritability of a 4 leafed clover?

Why hasn't there been a new breed of clover developed that was all 4 leafed?


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MKeeney
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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Wed Mar 14, 2012 2:23 am

Bootheel wrote:
What is the heritability of a 4 leafed clover?

Why hasn't there been a new breed of clover developed that was all 4 leafed?



if every clover was four leafed, then finding would one would be insignificant instead of years of good luck...and if we bred cattle to eliminate outliers, there would be no $100, 000 bulls, and we know the registered business needs $100,000 bulls...
EG,
would you agree that inbreeding regression is the result of homozygousity effect on quantatative traits...qualitative trait homozygousity is non-detrimental; at the simplest level, for example, color, polled etc
are not most convenience "type " traits likely qualitative? feet, udder, teat, temperament... tail switch? Smile or are things like tail switch and "femininity" merely manifestations of more complicated functions like hormones and such that would be quantatative?
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Mean Spirit



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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Wed Mar 14, 2012 9:00 am

Mike, I think I'm used to considering most traits that are not binary or close to binary (yes v. No, polled v. Horned, roan v. Red v white, etc) as quantitative traits. I don't think most type traits and convenience traits (udders, feet, tail switch, temperament) are close to binary- I think there is a fairly continuous range of phenotype in those traits. Practically, udders might be "good enough or not good enough", but it seems clear to me that they range from really good to nonfunctional, with a whole lot of gradations in between. So I think udders are quantitative traits in reality. I guess we don't commonly put a number on them to measure them- well, some do udder scores, I think the Dairy folks do a lot more- but the fact that we don't put a number on them yet doesn't make them not quantitative traits. Growth didn't have a number until people started weighing cattle, whenever that was, but impretty sure cattle were roaming around expressing growth as a quantitative trait for millennia before that.

I think.

Mean. Really Mean.
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whitecow



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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Wed Mar 14, 2012 10:42 am

I have seen data on estrogen, testosterone and just about every other hormone from pregnant cows and not found any significant differences based on fetal sex across the population. There may be differences from baseline in the individual cow, can't say that I have looked at that.
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MKeeney
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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Wed Mar 14, 2012 12:16 pm

Mean Spirit wrote:
Mike, I think I'm used to considering most traits that are not binary or close to binary (yes v. No, polled v. Horned, roan v. Red v white, etc) as quantitative traits. I don't think most type traits and convenience traits (udders, feet, tail switch, temperament) are close to binary- I think there is a fairly continuous range of phenotype in those traits. Practically, udders might be "good enough or not good enough", but it seems clear to me that they range from really good to nonfunctional, with a whole lot of gradations in between. So I think udders are quantitative traits in reality. I guess we don't commonly put a number on them to measure them- well, some do udder scores, I think the Dairy folks do a lot more- but the fact that we don't put a number on them yet doesn't make them not quantitative traits. Growth didn't have a number until people started weighing cattle, whenever that was, but impretty sure cattle were roaming around expressing growth as a quantitative trait for millennia before that.

I think.

Mean. Really Mean.
I don`t disagree....or at least not to the point of being mean spirited Smile so can a poor udder resulting from good enuff parents be the result of inbreeding depression? or just the recessives, unseen half etc, rearing it`s ugly, but more true, head?
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MKeeney
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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Wed Mar 14, 2012 12:18 pm

whitecow wrote:
I have seen data on estrogen, testosterone and just about every other hormone from pregnant cows and not found any significant differences based on fetal sex across the population. There may be differences from baseline in the individual cow, can't say that I have looked at that.
I`m just not too sure whitecow; afterall, I can determine sex before calving at about a 50% level...better % than I can a lot of other traits Smile Very Happy
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G nome



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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Wed Mar 14, 2012 12:20 pm

Mike, the primary gene pool for cattle would include all Bos genus as I see it, because crosses Brahman and British are fertile. Beefalo however are the result of gene introgression across strong fertility barriers that ultimately are dampened in later generations.
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G nome



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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Wed Mar 14, 2012 12:22 pm

whitecow, it has been my observation that cows 7 months or longer pregnant that show false heats and actively ride others usually give birth to bull calves.
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whitecow



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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Wed Mar 14, 2012 12:35 pm

There may be something to it. When I have some free time?! I'll look back through the data. We have much fewer samples for late term pregs but I'll see what's there.
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R V



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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Wed Mar 14, 2012 11:53 pm

Whitecow,
Just thinking about Free Martins. These are fraternal twins with two separate maternal-fetal units (Two chorions, two amnions) that should not have any direct crossover, but are in close physical contact. Other than through the maternal blood stream, how would the testosterone affect (get to) the female twin and why are most of the bull siblings to Free Martin heifers less fertile? The sex hormones are derived from cholesterol/fat and therefore shouldn't be transferred via amniotic fluid as obviously water and oil don't mix. Is there something different regarding the developing female's estrogen compared to the cow's estrogen? Every bull calf is exposed to his mother's blood and she has estrogen, but it doesn't seem to affect singleton pregnancy's future fertility otherwise the breed/race would disappear. Maybe the testosterone is different subtly or maybe it is a difference in fetal gonadotropins or fetal DHEA or some other hormone that we don't have a test for. I just checked and gonadotropins are glycoproteins and they could potentially be in the amniotic fluid, but I don't know how it could penetrate 2 amnions and then reach a high enough concentration in the amniotic fluid to affect the other fetus. We know that estrogen does cross through the placenta. In humans, we see the affect of it on babies after they are born. I have seen many parents over the years that were concerned because their babies have breast buds (male and female) and little girls will often have reddish discharge after they are born due to the sudden lack of exposure to maternal estrogen. Fetal blood does have a very different composition compared to adult blood because it needs to function at a lower pO2. Our current lab tests are designed for adult testosterone/estrogen and could very well miss a very similar, but slightly different molecule. Bonsa was much more observant regarding subtleties that most do not see. His uncanny ability to relate calving/gestational history of cows was apparently eerily correct. More than one older rancher that went to his seminars have related these stories. If he commented on a variance in hair quality with male and female gestations, I would suspect that this difference does exist and that it is hormonally related. Remember he relates most of his observations to a balanced endocrine system and he did this before much of our current knowledge. He noted the results of the "endocrine system" without knowing the shape, look, composition of many of the actual hormones, gonadotropins, etc. I suspect that we still haven't found them all nor all of their subtle variations.
Ron
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R V



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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Thu Mar 15, 2012 12:19 am

It's getting late, but just had another thought. The purpose of fetal sex hormones - estrogen and testosterone - is to differeniate the fetus as male or female for future reproduction. The purposes for these hormones later in life is for actual reproduction. If form follows function, then it stands to reason the sex hormones will have a slightly different form at this stage. Of course, there may be different and/or unknown factors that facilitate these changes that could produce the changes that Bonsma noted. I also suspect that fetal tissue sensitivity to these factors/hormones is heightened compared to the adult cow tissues otherwise they could/would affect her fertility.
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whitecow



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PostSubject: Re: Heterosis Needs a Homozygous Recharge   Thu Mar 15, 2012 12:52 am

First, my apologies for posting this hormone stuff on the wrong thread...the dangers of posting via my phone while driving.

If I remember correctly, the free-martin thing is caused by a protein hormone called anti-mullerian hormone. Both male & female fetuses are the same in very early development, but at some point the male fetus begins to produce anti-mullerian (sp?) hormone that causes the regression of the mullerian duct or female reproductive tract in a typical male fetus. This hormone makes its way to the female fetus in the case of male-female twins and produces a similar affect in the female fetus, ie free martin. I don't know why bull mates to free martin heifers might be less fertile. Estrogen & testosterone don't play very many unique roles in fetal development. I don't think the fetuses are a significant source of estrogen/testosterone until maybe late in gestation.
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