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Genetic Drift?

Y

Yankee Grower

cannaboy said:
Try some normal Male on female and you will get better stuff dude.
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Hell yeah. You can fool mother nature for a bit then she'll show you who's boss. Bruce Tainio, when alive, bred pest resistant strains of veggies but eventually they would succumb to stuff and he'd have to create a new strain which would last a bit then he'd have to start all over again. You can't fool Mother Nature :)
 
C

Cuzin_Dave

Active member
Genetic drift happens independent of selection.
Cannabis is pretty low on the scientific genetic research scale so very little is known about hybrid vigour, inbreeding depression and the effects of genetic drift.
Genetic diversity is of little commercial concern whether it be corn, cattle or cannabis.
The problem with cannabis is that extinct is forever. There were thousands of great lines that were never worked and never fulfilled their potential.
It is a matter of being value neutral as to whether or not inbreeding or out crossing from small populations is beneficial or harmful.
Genetic drift is a corollary of breeding closet populations. That does not mean people should stop breeding plants.
 
englishrick

englishrick

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these are some wickid Quotes Dave,,,thanks for posting that Chapter:)

"The loss of alleles via genetic drift has two effects: First, it increases homozygosity; consequently, it has an effect similar to that seen for inbreeding. The simultaneous effect of an increase in inbreeding and the loss of alleles via genetic drift as a result of a decrease in Ne can cause severe genetic problems. Secondly, the loss of alleles reduces genetic variance. Genetic variance is the raw material with which selection works. A reduction in genetic variance can make selection difficult, if not impractical. If there is no genetic variance, there will be no heritable differences, which means that selection cannot improve a phenotype. Equally important, if the population is being cultured for stocking lakes and rivers, the loss of genetic variance may doom the project to failure. Natural populations need broad gene pools (i.e., they need as much genetic variance as possible), because it is impossible to predict what genotypes and what alleles will be needed to ensure survival. Populations with narrow genetic bases are less likely to survive in the long term."



"Many factors can cause changes in gene frequency; among them are: selection by the farmer or hatchery manager; domestication, genetic drift."

The changes in gene frequency caused by selection and domestication usually produce genetic improvements,,,, In contrast, the changes in gene frequency that are caused by genetic drift are random, which means they can be counterproductive."

"Genetic drift is random changes in gene frequency,,, it is a major factor in evolution and population biology...like inbreeding, it too must be considered if hatchery populations are to be properly managed."

"Genetic drift can be as important as selection in altering a population's gene pool. The effects of genetic drift can be devastating. Genetic drift can irreversibly alter gene frequencies and eliminate alleles, which can decrease a population's ability to survive or to adapt to an altered environment, and it can preclude future selection. The effect that genetic drift can have on a population's gene pool can make many management goals impossible to achieve."
 
Texicannibus

Texicannibus

noob
Veteran
Cuzin_Dave said:
Genetic drift happens independent of selection.
Cannabis is pretty low on the scientific genetic research scale so very little is known about hybrid vigour, inbreeding depression and the effects of genetic drift.
Genetic diversity is of little commercial concern whether it be corn, cattle or cannabis.
The problem with cannabis is that extinct is forever. There were thousands of great lines that were never worked and never fulfilled their potential.
It is a matter of being value neutral as to whether or not inbreeding or out crossing from small populations is beneficial or harmful.
Genetic drift is a corollary of breeding closet populations. That does not mean people should stop breeding plants.
Click to expand...

So Dave your saying here that selection is irrevelant? It seemed that article I sited seemed to find some relevance although the enviroment was also cited as a possible reasoning for the sustained genetic diversity from a single pair of animals breeding many generations and creating populations up to 700 animals. All without losing genetic diversity. Im not arguing just trying to clarify. What would be the reasoning you have for the article I sited as for the sustained genetic diversity?

It seems like from what I can gather that genetic drift isnt the given that modern science seems to be suggesting. Rather its a likely result of combining limited numbers.
 
V

VenturaHwy

Active member
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very oldman said:
I kind of remember Mr Nice had a viral problem with their cuttings many years ago,just remember reading somthing from Shanti about the drama it caused.could it be somthing like that? just a thought. mostly cutting will go indefinatly!
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I grew the same plant since '84, always took cuttings right before flowering, never kept a mother plant. For the first 7 or 8 years not really sure, the plant was perfect. Then it got a virus.... but it was still the same plant, never produced a single male flower in all those years. Just recently got rid of it.

I wish you guys would post some picts, it would be interesting to see what ya got.
 
englishrick

englishrick

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i think selection in general causes allele frequencies to change and "directional selection" eventually leads to the loss of all alleles except the favored one,,,

but some forms of selection, such as "balancing selection" lead to equilibrium without loss of alleles....

Wiki said:
Balancing Selection

Balancing selection refers to a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies above that of gene mutation. This usually happens when the heterozygotes for the alleles under consideration have a higher adaptive value than the homozygote. In this way genetic polymorphism is conserved.

There are three main types of natural selection: In directional selection the allele frequency for a trait continuously shifts in one direction. In stabilizing selection the frequency of the alleles of lower fitness decreases until they vanish. Balancing selection is similar but not identical to disruptive selection where individuals of extreme trait values are favored against those with average trait values. These terms are used for quantitative characters controlled by a number of genes

Evidence for balancing selection can be found in the number of alleles in a population which are maintained above mutation rate frequencies. All modern research has shown that this significant genetic variation is ubiquitous in panmictic populations. It is a genetic expression of the field experience of Darwin, Wallace and others, that natural populations in the wild are extraordinarily varied (though not all such variation is of genetic origin).

There are several mechanisms (which are not exclusive within any given population) by which balancing selection works to maintain polymorphism. The two major and most studied are heterozygote advantage and frequency dependent selection.


The Heterozygote Advantage
In heterozygote advantage, or heterotic balancing selection, an individual who is heterozygous at a particular gene locus has a greater fitness than a homozygous individual.

A well-studied case of heterozygote advantage is that of sickle cell anemia in humans, a hereditary disease that damages red blood cells. Sickle cell anemia is caused by the inheritance of a variant hemoglobin gene (HgbS) from both parents. In these individuals hemoglobin (protein in red blood cells that carries oxygen to the tissues) is extremely sensitive to oxygen deprivation causing short life expectancy. However, a person who inherits the sickle cell gene from one parent and a normal hemoglobin gene (HgbA) from the other parent (this person is said to be a carrier of the sickle cell trait) has a normal life expectancy (though these heterozygote individuals may suffer periodic problems).

The heterozygote is resistant to the malarial parasite which kills a large number of people each year. This is balancing selection between fierce selection against homozygous sickle-cell sufferers, and selection against the standard HgbA homozygotes by malaria. The heterozygote has a permanent advantage (a higher fitness) wherever malaria exists.


Frequency Dependent Selection
Frequency dependent selection occurs when the fitness of a phenotype is dependent on its frequency relative to other phenotypes in a given population. In positive frequency dependent selection, the fitness of a phenotype increases as it becomes more common. In negative frequency dependent selection, the fitness of a phenotype increases as it becomes less common. For example in prey switching, rare morphs of prey are actually fitter due to predators concentrating on the more frequent morphs.


Fitness Varies in Time & Space
The fitness of a genotype may vary greatly between larval and adult stages, or between parts of a habitat range.
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Grat3fulh3ad

Grat3fulh3ad

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Texicannibus said:
So Dave your saying here that selection is irrevelant? It seemed that article I sited seemed to find some relevance although the enviroment was also cited as a possible reasoning for the sustained genetic diversity from a single pair of animals breeding many generations and creating populations up to 700 animals. All without losing genetic diversity. Im not arguing just trying to clarify. What would be the reasoning you have for the article I sited as for the sustained genetic diversity?

It seems like from what I can gather that genetic drift isnt the given that modern science seems to be suggesting. Rather its a likely result of combining limited numbers.
Click to expand...

IMHO and IMHE,

One of the effects of proper selection it to mitigate drift by culling weakness (similar to nature) or undesirable traits (like dioecious-ness), and by selecting the strongest truest representatives of the line.

You can breed a genetically sustainable population with suitable diversity following a bottleneck. You can also end up with a failed experiment with a high incidence of weaker individuals. (on a side note: monoecious lines are more prone to inbreeding issues, while true dioecious lines are much less likely to develop them) Genetic drift is not a given, you are correct, it is probabilistic depending on several different factors, population size being only one of them.

To some degree the population size issue has always reminded my of "polling" to determine the statistical views of the entire nation. There is a poll sample size which it too small to be significant... but once a significant sample size is reached, increasing the number of people questioned no longer increases accuracy, but it does increase margin of error.


If mankind were completely uninvolved in cannabis propagation, then every isolated population will still continue to change and diverge over time.
 
Texicannibus

Texicannibus

noob
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Grat3fulh3ad said:
IMHO and IMHE,

One of the effects of proper selection it to mitigate drift by culling weakness (similar to nature) or undesirable traits (like dioecious-ness), and by selecting the strongest truest representatives of the line.

You can breed a genetically sustainable population with suitable diversity following a bottleneck. You can also end up with a failed experiment with a high incidence of weaker individuals. (on a side note: monoecious lines are more prone to inbreeding issues, while true dioecious lines are much less likely to develop them) Genetic drift is not a given, you are correct, it is probabilistic depending on several different factors, population size being only one of them.

To some degree the population size issue has always reminded my of "polling" to determine the statistical views of the entire nation. There is a poll sample size which it too small to be significant... but once a significant sample size is reached, increasing the number of people questioned no longer increases accuracy, but it does increase margin of error.


If mankind were completely uninvolved in cannabis propagation, then every isolated population will still continue to change and diverge over time.
Click to expand...

Thanks for the response Head, I agree. It would seem that the article I sited more or less shows selection (natural selection in the article) and culling(enviromental hardships in the article) would limit drift and/or possibly halt it.

The poll analogy is interesting and thought provoking. Good analogy and relatively accurate IMHO.

It would seem to me with or without mankinds envolvement in cannabis propagation that it would have potential to evolve(change /diverge). I think that we can both help and hinder the process.

Im curious since we are talking genetics what effects you guys believe nuetrinos*sp have had on evolution. The other major question I have about genetics that Id value yalls opinion on is do you think evolutionary changes happen ultra slow or ultra fast? I know this is derailing a bit ... but imo not to terribly much. Genetic drift imo atleast is a theory that supports ultra slow evolution although I can easily be wrong about that.

link to nuetrino info:
http://www.ps.uci.edu/~superk/neutrino.html
 
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Texicannibus

Texicannibus

noob
Veteran
Ok thats kinda a crap link rather old info on nuetrinos. The way I understand these particles is that they basically can pass through anything known to man. They can interact with cells and cause mutations. There is a large group of researchers who believe that neutrinos are responsible for fast mutations in genetics. There is also some support for the belief that the interaction with cells in your body could lead to cancer(mutated cells).
 
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