I'm first and foremost a computer scientist, molecular biologist second. I've got a very superficial understanding of some of the topics discussed on this site. Therefore I'm starting this thread to ask questions about subjects discussed on this site I do not understand well.

One of these is population genetics and evolution. One claim I think I've read here is that if there has been different selection pressures on a trait in two different populations, you'd expect to see the greatest population difference in those alleles with the largest effect on said trait. Is this correct? If so, is this a theorem of some sort with a name?
[hr]
Another one about quant. gen: are there traits ( in any species) one has tried to breed for, but been unable to?

I'll try, although I'm not sure I understand your question. But if you ask whether a given trait will have more phenotypic difference between populations if the traits in question are those more subjected to selection pressures. I will answer yes.

If you're interested, P Frost has a post on Lewontin's Fallacy, where he mentioned this point, about researchers using genetic markers of low(er) selective value. This illustrates the idea.

One claim I think I've read here is that if there has been different selection pressures on a trait in two different populations, you'd expect to see the greatest population difference in those alleles with the largest effect on said trait. Is this correct? If so, is this a theorem of some sort with a name?

Here's a paper which employed a more sophisticated version of Davide's method: Berg, J. J., & Coop, G. (2014). A Population Genetic Signal of Polygenic Adaptation. PLoS genetics, 10(8), e1004412.

Regarding selection on alleles, I will look for a formal proof, but this is common wisdom (and it makes intuitive sense). For example, Hawks notes:

"Stature may be affected by hundreds of loci, but these do not account for equal proportions of the additive variance. Loci are subject to selection roughly in proportion to the additive variance in fitness they explain. Directional selection on stature will change the allele frequencies for a few loci quite a bit more quickly than most."

http://johnhawks.net/weblog/topics/evolution/selection/pritchard-di-rienzo-polygenic-adaptation-2010.html

Thank you. I can see how it makes intuitive sense so no need for a proof.

One of these is population genetics and evolution. One claim I think I've read here is that if there has been different selection pressures on a trait in two different populations, you'd expect to see the greatest population difference in those alleles with the largest effect on said trait. Is this correct? If so, is this a theorem of some sort with a name?
[hr]
Another one about quant. gen: are there traits ( in any species) one has tried to breed for, but been unable to?

Yes that was a claim of mine that I made in some previous post on this website (http://openpsych.net/forum/showthread.php?tid=117&pid=1029#pid1029)
However, I do not know if there is a theorem or a formal proof. Intuitively it makes sense.

Isn't this something you could test with the current height SNPs? Low hanging fruit...

(If the effect sizes of the current SNPs are approx the same, this might not be possible.)

Isn't this something you could test with the current height SNPs? Low hanging fruit...

(If the effect sizes of the current SNPs are approx the same, this might not be possible.)

Well I had found that the SNPs with the lowest p value (thus bigger effect size) had the highest loadings on the PC...but this correlation was not really big (around 0.25)