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Number of generations till a strain is stable

WhamGenetics

WhamGenetics

This topic was started in response to another thread, before people try to blow me out of the water on this, understand that in most cases I would advocate going to F7+ before I'd say it's stable with a gun to my head. But the following is ment to spark discussion on the genetic mechanisms and pathways that lead to stability.
In particular it is in response citing this link and its general claim that heterozygosity is halved every generation, thus it never reaches % 100 :
http://kdcomm.net/~tomato/gene/genes2.html

Which in my opinion is a very good resource but makes things simple by leaving out details that are relevant for this discussion.

For one, this example only holds if every gene with a phenotype segregates independently. But they don't, they are physically linked on chromosomes. Capsicum has 12 chromosomes, so ignoring recombination an F1 crossed back to it self will produce F2s that have 0-12 heterozygous chromosomes with an average of 6. A randomly selected F2 then crossed back with itself will then produce an F3 generation with 0-12 Heterozygous chromosomes with an average of 3. And so on F4 = 1.5, F5 = 0.75....

What's interesting is that these are only averages, so for instance in the F2 generation 1 out of every 4096 plants is already homozygous at all 12 chromosomes and in the F3 one in every 64 is ! You just have to be smart or lucky enough to know which one. My point being that, even after only 4-5 generations you have a descent chance of having stable individuals if your growing out several many dozen every generation and if your using stability as a selected for trait your not going to require as many generations as you would if you were relying on chance alone.
 
sounds like some of the hillbillies have been a nippin'.

so, to add some very minor intelligence to your post....very minor.... i have always been curious about people who ask for red savina seeds. how does one know that they are getting the real mccoy? i can buy red savina locally but they come from GNS spices(the originator). if i grow them out, they shouldn't be F1 any longer. would the seeds be red savina or would they be something else. so, if i purchased GNS red savina, grew 1 plant and it gave me 20 pods, i then saved 2 seeds from every pod and planted those seeds and assuming each seed germinated and grew to maturity and each plant delivered 20 pods, what would that generation of F2's give me, assuming i took 2 seeds from every pod. would the grand children grow true or would they be something else, or would i get a combination. would several plants give me red savina equivalent and others more red habanero'ish and several others something else(whatever gns mixed to create the red savina). would i then have to select just the pods from the F2 generation that most resembled a red savina and grow them out in a similar fashion, only to select just the pods that most resemble red savina in the F3 generation. and so on, and so on.

i have superchili plants that where originally stated as superchili F1, but i have since grown great grandchildren and they look and taste just like the original plant, some 15 years ago. but i cringe everytime i read a post asking to trade red savina.
 
WhamGenetics said:
This topic was started in response to another thread, before people try to blow me out of the water on this, understand that in most cases I would advocate going to F7+ before I'd say it's stable with a gun to my head. But the following is ment to spark discussion on the genetic mechanisms and pathways that lead to stability.
In particular it is in response citing this link and its general claim that heterozygosity is halved every generation, thus it never reaches % 100 :
http://kdcomm.net/~t...ene/genes2.html

Which in my opinion is a very good resource but makes things simple by leaving out details that are relevant for this discussion.

For one, this example only holds if every gene with a phenotype segregates independently. But they don't, they are physically linked on chromosomes. Capsicum has 12 chromosomes, so ignoring recombination an F1 crossed back to it self will produce F2s that have 0-12 heterozygous chromosomes with an average of 6. A randomly selected F2 then crossed back with itself will then produce an F3 generation with 0-12 Heterozygous chromosomes with an average of 3. And so on F4 = 1.5, F5 = 0.75....

What's interesting is that these are only averages, so for instance in the F2 generation 1 out of every 4096 plants is already homozygous at all 12 chromosomes and in the F3 one in every 64 is ! You just have to be smart or lucky enough to know which one. My point being that, even after only 4-5 generations you have a descent chance of having stable individuals if your growing out several many dozen every generation and if your using stability as a selected for trait your not going to require as many generations as you would if you were relying on chance alone.
Click to expand...

Zeno's paradox in genetics....makes my head hurt.

But on to the stability...yes you are correct that after 4-5 generations your "breed" will be relatively stable, but you must continue to select offspring for the desired traits or else your "strain purity" will degenerate rapidly. Once the seed is being collected and regrown by others it becomes muddied.

So I'd say if you want strain purity the originator must continue to select his strain and be the sole seed supplier for it. All seed from other growers will, in time, deviate from the original.

Asexual reproduction or cloning of plants is the only way to produce 100% consistency.

I've been wondering why more people aren't growing pepper clones?
 
Such a better read sober. Another thing I have seen is some people when growing out will switch what they select for 3 or 4 generations in. From what I have seen and read you must set what you are selecting for and stick to it for best results. Like AJ and his selection for stingers.


+1 Armac....FG is quite knowledgeable in this area.
 
POTAWIE said:
Vendors sometimes mislead people by calling their stable plants f1 hybrids so people are forced to buy seeds :(
I like to grow my crosses out for at least 9 generations before I consider them stable but I'm still learning a lot
Click to expand...
Agreed, I can see why there would be incentive to sell an F1 that could be reliably produced by the seller but breakdown after that.

thegreenman said:
Zeno's paradox in genetics....makes my head hurt.

But on to the stability...yes you are correct that after 4-5 generations your "breed" will be relatively stable, but you must continue to select offspring for the desired traits or else your "strain purity" will degenerate rapidly. Once the seed is being collected and regrown for others it becomes muddied.

So I'd say if you want strain purity the originator must continue to select his strain and be the sole seed supplier for it. All seed from other growers will, in time, deviate from the original.

Asexual reproduction or cloning of plants is the only way to produce 100% consistency.

I've been wondering why more people aren't growing pepper clones?
Click to expand...

Yea there are many other plants that are traded as clones, I would think it would be feasible with peppers. Wonder why it's not done more often.

In regards to zeno's paradox, I guess that's what I'm saying doesn't happen in this case. The model being shown in this artical does not take into account genetic drift or linkage. So yes in theory the average does follow zeno's paradox in an infinite population but in practice in a small population with linked genes it's likely to happen more quickly, and completely. That is, they reach 100%.

Also consider if a breeder were able to take advantage of genetic technology. I could order a genetic marker for each side of every chromosome. If I was pressed for time I could screen the 4096 individual necessary at the first leaf stage of the F2, then make seed stock out of that one individual that is homozygous, and then those F3s will be totally stable.
 
Depends what's affordable to you. If you wanted to throw 20-30 k at it you could get started.

So it's available for corporations and some elite few individuals.
 
WhamGenetics said:
Depends what's affordable to you. If you wanted to throw 20-30 k at it you could get started.

So it's available for corporations and some elite few individuals.
Click to expand...

Yeah well that's definitely not affordable for most people, including me. Also the "home" part is missing. I'd say when it would cost less than a few hundred $$$ per sample, then serious hobbyists and small-scale hybridizers could afford to do it on several strains and be reasonably sure to see some ROI, with the possibility of marketing a unique strain to the small group of gardeners who would be interested in such a thing. Why would you bother if you couldn't recoup your investment from the resulting product?

I have a feeling these things are only a few years out... and will be commonplace within a decade. For example look at the home paternity testing kits...they cost less than $100 now....
 
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