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Old 09-19-2017, 07:38 PM #1
trichrider
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Question let's hear your thoughts...

hey.

i want to produce some seeds with as much genetic diversity as possible, with as few plants as possible.
this is my theory.

i started about 40 plants from seed (regular seed).
out of those i chose the most vigorous, maybe 20.

instead of one spectacular specimen of male plant i've kept at least 3 (so far showing) and multiples of that for females.

this should avoid bottle-necking correct?

i'm not out to resurrect the strain, just to keep viable diversity of seed-stock on hand.

opinions are ok too. thnx.
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Old 09-19-2017, 08:33 PM #2
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You might find more help posting this in the Breeder's Laboratory, posts stick around a a lot longer there.

the more males the better, i think
you are going to have a shit load of seeds.

good luck
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Old 09-19-2017, 09:07 PM #3
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For genetic diversity you need little selection, so more parents is better and keep also the not so vigorous individuals.
But you should start with all different lineages for example three different indica males with five different sativa females will give you many hybrids with huge variations. Not sure what to do with all the seeds, may be hard to search for a killer plant to keep, might be cool to throw them around in spring.
All depends on your goal.

I like crossing two different F1's and see what happens, similar approach to yours but with only two plants.
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Old 09-19-2017, 09:35 PM #4
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For some reason the number 30 comes to mind. Obviously the more plants you have the more diversity there will be. But I think 30 is a number that will give you the most diversity with the fewest plants out of a given population.

I think Tom Hill made some comments about this but not sure, most of his posts are gone.
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Old 09-19-2017, 10:17 PM #5
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This also depends heavily on where you're starting.

A true F1 requires just one selfed plant to recover all of the genes. Same for an idealized inbred line (cannabis requires too much heterozygosity to achieve this goal, but in principle). Both of these cases are true because the parents have essentially no genetic diversity.

The outcomes would be very different, though: uniformity in an inbred line, extreme diversity in the F2 generation.

We're stuck with some variation of the latter. SamS has posted a link to studies of just what number of plants are required in each stage. It's actually more like 1000s to preserve a complete population! I'm short of time otherwise I'd point you to it.
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Old 09-19-2017, 10:51 PM #6
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Remove any off types, things that aren't what you care for. Examples may include, early flowering males, very vigorous and tall growing males, hermaphrodites, structure of the plant etc. Supposedly some would say hollow stems are good indicators of higher thc, but I have only heard this and not sure about it myself. If you compile a list of the things you require for the characteristics of the variety, you should be able to rouge out what you don't want and keep as many plants as possible for what you do want.
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Old 09-21-2017, 06:12 AM #7
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Quote:
Originally Posted by trichrider View Post
hey.

i want to produce some seeds with as much genetic diversity as possible, with as few plants as possible.
this is my theory.

i started about 40 plants from seed (regular seed).
out of those i chose the most vigorous, maybe 20.

instead of one spectacular specimen of male plant i've kept at least 3 (so far showing) and multiples of that for females.

this should avoid bottle-necking correct?

i'm not out to resurrect the strain, just to keep viable diversity of seed-stock on hand.

opinions are ok too. thnx.
If your desire is to keep some diversity within a given line, what you describe will work.
But... As suggested above, more parents will give more diversity.

I think I remember reading that it takes a field of 20,000 males & 20,000 females in order to not lose diversity. I doubt anybody has that kind of space to breed with.
Maybe Sam.
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Old 09-21-2017, 03:51 PM #8
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Post

FYI:

Quote:
Originally Posted by Sam_Skunkman View Post
And a classic that explains the problems maintaining Cannabis landraces in a closet.
1,000 males and 1,000 females are required to avoid serious gene loss, because Cannabis is an dioecious obligate outcrosser.
-SamS

Theor Appl Genet (1993) 86:673-678
Statistical genetic considerations for maintaining germ plasm collections
J. Crossa , C. M. Hernandez , P. Bretting , S. A. Eberhart , S. Taba
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Old 09-21-2017, 05:25 PM #9
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Quote:
Originally Posted by zif View Post
FYI:

That was based on the Wang/crossa work that Rob Clarke looked at, the number was to conserve all the alleles, this is a post from the thread it was discussed in;

Quote:
Sam, I should have metioned that my argument was based on my recollections of constructing those statistical tableaus with Ne on the left hand side and very small numbers on the top of the matix.So your argument about Ne at 2000 would be correct insofar as preserving almost all of the alleles. Anyways doing too much math makes my head hurt. The little ^ symbols I used are exponentials.
There are methods for estimating the probability of genetic drift and underscoring its devastating impact on unsystematic shifts in allele frequencies where Ne is small.
The formula is: Prob. = (1 - frequency) ^ 2 ^ Ne
For example, lets say there is a less common allele (w) in a white widow clone that occurs say 5% of the time (.05) and further for arguments sake Ne = 2.
So. (1.- .05) = .95
(.95) ^ (2)(2) = 81.4% probability of elimination
Make Ne = 50
(.95) ^ (2)(50) = .00592 probability of elimination.
As is the case with any algorithm, the answers will change depending upon what numbers one intends to plug into the formula.
The higher the frequency of an allele in a given population the greater its likelihood of surviving a genetic bottleneck with the opposite being true of lower frequency alleles surviving when Ne is very small.
To expand on the basic concept of Ne one must consider how Ne effects the F statistic (Coefficient of Inbreeding).
So let's assume an NE of say 4. The decline in heterozygosity or rate of inbreeding at from the first generation would be: F1 = (1) / (2 * Ne) or 1 / (2 * 4) = .125.
With each subsequent generation the decline in heterozygosity is cumulative. Take generation F6
F6 = 1 - (1 - F1) ^ 6 = 1 - (1 - .125) ^ 6 = .551
By the 6th generation 55% of the genetic diversity will have been lost in the line. By the 12th generation 1 - (.87.5) ^ 12 = 80 % of the genetic diversity will have been eliminated.
The larger the Ne the lower the rate is the actual loss of diversity through inbreeding.
Let's take a hypothetical example:
Breeder X grows out 20 plants and gets 6 males and 14 females.
Effective breeding population will be:
(4)*(6)M*(14)F / 20 Plants Total =16.8

Change in inbreeding per generation:
1 / (2)*(16.8)= 2.9%

The "best" effective size calculation in this example:
16.8/20 = 84%

Fun with numbers for sure. I posted these examplea to underscore that genetic drift is quantitatively measurable.

As you can see from the above the more the better, now if for example you took an example like Tomhills haze were he stated 5% were the great ones giving you 5/100 or 1/20, you need 20 to make sure you capture that 1.

https://www.icmag.com/ic/showthread....=drift&page=42
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Old 09-21-2017, 10:32 PM #10
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The drift calculations, as you point out, show more is better. And it's tough, because ensuring just a given allele is preserved takes tons of plants. It's far worse given that we want entire ensembles of alleles!

Quote:
Originally Posted by Yard dog View Post
As you can see from the above the more the better, now if for example you took an example like Tomhills haze were he stated 5% were the great ones giving you 5/100 or 1/20, you need 20 to make sure you capture that 1.
Your example is much trickier than this. You cannot count on getting a great thh with just 20 plants. Any given 20 plant grow, with 1/20 being 'great', has a 36% chance of not showing that rare 'great'! I'm not sure about you, but I think making sure you capture that greatness would mean having, what, a 90, 95, or maybe even 99% chance of finding the 1/20 type?

These levels of certainty require 45, 59, and 90 plants, respectively. But maybe we should account for females? Then we'd need roughly double the plants to be 'sure' to capture the 'great' type. The math is simple, but the implications are challenging!
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