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Re: RE:Hyb: Cytoplasmic inheritence was disease resistance {Walter]


I was thinking about the maternal inheritance at work today.  I was powerwashing the fueling area at a truck stop, so my mind wasn't being used otherwise.
I recalled a discovery of a couple of years ago.  
DNA from the father, either in plants or animals, is somewhat methyated.  DNA from the mother is not.  These methyl groups stay on the DNA for the whole generation, that is, for the life of the seedling.  
Methyl groups are molecules of methyl alcohol, chemically bound to the chromosomes.
Then during the process that produces gametes for the next generation, the methyl groups are removed, and they are not put back on when making the eggs, but they are put on the new chomosomes in the pollen or sperm.
So what do the methyl groups do?  They reduce the effectiveness of the DNA.  Someone mentioned that onco x TB has more of an onco look than a TB x onco.  Methylization could account for this.  If methylization is the sole cause, then the direction of the cross would influence the look of the F1 hybrids between arils and TBs or Arils and SDBs, etc.  But the direction of the cross would not effect the breeding value of the resulting hybrids, because the methylization would be removed in the offspring from its seeds.  And the methylization would be added to its pollen, regardless of the directin of the origional cross.
I have not heard any explaination for why this methylization occurs.  It does not seem it would help to have the paternal DNA less subject to selection than maternal DNA.  I have read little about it since the flury of publishing when this was discovered.  At that time, biologists generally said it was counter intuitive.  Not only could no one think what good it would do, most said that at first glance, it seemed to be a bad idea.  But if it didn't help, surely it would have been selected against.
This would seem to sugest that one use the better iris as the seed parent in crosses, for best results.
And it could relate to TB x I. tectorum vs. I. tectorum x TB, as well as tb x aril vs. TB x arils.
Likewise all those beardless crosses.
It should not explain the peanut crosses, because those took until the F3 generation to disapear.  Methylation should only be noticable in the F1.  Still more to learn.
Walter

Neil A Mogensen <neilm@charter.net> wrote:
That peanut phenomenon is intriguing, Walter. I haven't the foggiest of how
it might be explained either.
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