Genetic Drift?

[Cuzin_Dave]

There are very practical reasons for maintaining genetic variation in a population.
If diversity gets reduced the possibility of improving a seed line declines and the line may not respond well to selective pressure.
If the population is small, the loss of potential valuable alleles in a line becomes unsystematic.
The population will change by randomness rather than selection.
One has to wonder how much genetic diversity exists among all the commercial hybrid strains being pitched and promoted by most of the seed vendors these days.
The important thing to consider is that having an Ne of 2 or 4 is a surefire recipe for genetic drift and permanently eliminating potentially valuable genetic information from a seed line by mere chance.
Working with microscopic closet populations reduces breeding to buying a lottery ticket with very small odds of a payoff.

 

[dank.frank]

What then would you suggest as a minimal population of males to use for pollination then? Not for commercial production, but even so that it is worth the time of the end user to toss pollen for the purpose of preserving a line they purchased???


dank.Frank

 

[Jones]

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[love?]

Haven't found the 1999 article but the article by Wang et al. 2004 that I attached in my previous post also addresses some of the shortcomings of Crossa's 1993.

Might you mean this one:

Variance Effective Population Size under Mixed Self and Random Mating with Applications to Genetic Conservation of Species
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[SIZE=-1]R Vencovsky, J Crossa - Crop Science, 1999 - Crop Sci Soc America

http://crop.scijournals.org/cgi/content/full/39/5/1282

Free full text.
[/SIZE]

 

[Jones]

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[Sam_Skunkman]

I think the real lesson is that conservation requires a minimum of several thousand plants per variety to avoid gene loss. The Wang article above mentions that you can not consecutively grow out smaller batches of say 200 plants, for 10 years in a row and have the same result as a single grow of 2000 plants. Gene loss will be higher in the first case of the smaller grows. For conservation this is vital, for plant breeding just important.

-SamS

 

[englishrick]

how are the numbers effected when we work with feminized lines??,,,,

is it not easyer to preseve suiprior genotypes via feminization rarther than regular M/F breeding?

 

[Sam_Skunkman]

I was talking about Conservation of lines, not breeding. To me all female lines are not a conservation method to save superior genotypes. Clones, maybe, but who has clones older then 20 years? I have frozen seeds much longer. Conservation entails 1,000+ males, 1,000+ females allowed to freely pollinate, albeit with removal of a few bad/off plants.
-SamS

 

[kopite]

I think the real lesson is that conservation requires a minimum of several thousand plants per variety to avoid gene loss. The Wang article above mentions that you can not consecutively grow out smaller batches of say 200 plants, for 10 years in a row and have the same result as a single grow of 2000 plants. Gene loss will be higher in the first case of the smaller grows. For conservation this is vital, for plant breeding just important.

-SamS

We have been thru this before in the thread mentioned earlier.... Hyb thru out some good stuff that got deleted and here we are now wheel spinning...

Kopite

 

[kopite]

Anyways, that was long ago and we should look into newer revisions and/or adaptations of Crossa's 93 work. I particularly like the Wang 2004 article.

have you used any of his simulations ? he is someone I like..

http://www.cimmyt.org/english/wps/news/2006/jan/conserv_byNumbrs.htm
http://www.generationcp.org/arm.php
http://crop.scijournals.org/cgi/reprint/43/5/1764

 

[englishrick]

To me all female lines are not a conservation method to save superior genotypes. Clones, maybe, but who has clones older then 20 years?

but feminization is a conservation tool,,,is it not??,,,

feminization can be used to create populations and they are effected by genetic drift,,are they not?

i have 2 clones that are around 20 years old ,,"good old skunk types",,,,your style!

thanks ,,

 

[englishrick]

all fem lines are a good part of larger breeding programs!!

selfing ensures that sutch supirior genotypes will not quickly be lost as a result of segregation when hybridization occures

 

[Jones]

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[John Public]

Conservation entails 1,000+ males, 1,000+ females allowed to freely pollinate, albeit with removal of a few bad/off plants.

When I looked further into how genebanks deal with preservation things got even more complicated. Maybe you remember the preservation done in/ex situ mess that I created in the thread you mentioned before. Anyways, I'm frustrated that there's no 'how to preserve cannabis for dummys' like me that covers all (cannabis) relevant points.

edit: sorry if I double post some informations, I had not all the time necessary to read all the 29 pages of the topic.

Indeed there is a major issue there. There is the problem of the alleles frequency and the number of loci that you want to preserve. After all, what is really preservation?

With Cannabis, these are sub species that need to be preserved, not species, hence most of the questions rised by Biological Conservation research do no fit well as it is more focused on "how to preserve a species" rather than "how to preserve part of genotypes of this species in a sub population of this species". Most populatioin viability analysis focus on how many individuals of a species we need so that it does not disappear.

So what are we willing to preserve when we say "a Cannabis line"?

How many traits and how many genes linked with this traits?

Do we need really to preserve all genotypes of all sub species or could not we just preserve the main special traits of each special Cannabis sub strains AND one strain that would be preserved at the whole genetic potentiel level?

How did these special Cannabis line appeared? Throug natural selection pressure or man-hand selective pressure or finally both in the areas where Cannabis man grown is mixed with escaped individuals?

Last point, even if you can grow 10 000 individuals of your line, if the environment is very different from the natural environment of the line, you'll have a stronger bottle neck than with 1000 individuals grown in a environment closer to the original one, because of the strong selective pressure you'll put on your population.

So discussing the genetic drift and giving numbers without taking into account the pressure induced by the environment of the preservation area is not realistic imho. I'd prefer Thai seeds of a small indoor closet of 50 individuals for 5 generations than seeds of the same line from a field of 1000 individuals located outdoor in Norway for the same number of generations.

 

[Sam_Skunkman]

Last point, even if you can grow 10 000 individuals of your line, if the environment is very different from the natural environment of the line, you'll have a stronger bottle neck than with 1000 individuals grown in a environment closer to the original one, because of the strong selective pressure you'll put on your population.

So discussing the genetic drift and giving numbers without taking into account the pressure induced by the environment of the preservation area is not realistic imho. I'd prefer Thai seeds of a small indoor closet of 50 individuals for 5 generations than seeds of the same line from a field of 1000 individuals located outdoor in Norway for the same number of generations.

With a greenhouse with heat and lights I think you are wrong, but if you can't grow the crop however, wherever, to full maturation, for any reason then of course you would be right.

-SamS

 

[DocLeaf]

I was talking about Conservation of lines, not breeding.

Nail on the head! you gotta get up dam early to catch Sam out kids! He's on the roll

 

[Broccoli Head]

all fem lines are a good part of larger breeding programs!!

Not even close.

 

[DocLeaf]

Smaller breeding programs perhaps,, but otherwise we would NOT use fem. seeds to make steady lines from..! They are inbred to themselves only!

We crossed a regular male with a clone from reliable feminized seed stock last season ,,, just to test the ability of feminized seeds as parent plants.,, here

So far so good ...

'Painted Lady' = Critical [RQS] fem. X W.Widow FreeTibet [So7omon seeds] reg.

We will have to see what happens... and if they drift from here.. lol

 

[krunchbubble]

wish i understood what you guys are saying.............its like you guys are speaking Japanese.......

 

[Cuzin_Dave]

Cannabis breeding, if one wants to call it that these days, is the last frontier for the scientifically and mathematically challenged. Calling what is going on these days breeding is laughable and just about everyone would be a whole lot better off breeding their own lines and seed saving for the next crop. The whole purpose of making any F1 cross is to produce offspring that are genetically superior to the parental lines. Those assumptions must be tested against empirical evidence and if they don't then the argument is false.
Closet breeding is a benign activity at the private level, but when it overtakes the whole culture there is a problem. People breeding cannabis are not unlike kennel owners who raise purebred dogs where the Ne is very small. Needless to say there are better and worse dog breeders out there. There is not much evidence to suggest that mixed breed dog will always exhibit hybrid vigour or that a purebred dog is inherently genetically inferior. It boils down to good breeding practises whether it be cannabis or dogs or whatever.
People who wants to breed their own lines and are serious about it generally start with something relatively stable like Skunk rather than some octahybrid from the XYZ Fly by Night Seed Company. Spending 5 years growing out F2's in no big deal and lots of fun.
Working with a known phenotype from a stable line and a small population is a whole lot easier than a seed line that spits out 256 gross phenotypes at F2.