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Genetic drift vs Genetic flow

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Genetic drift vs Genetic flow

Postby bionewbie » Thu Mar 30, 2006 2:43 am

I don't know, for some reason I have a lot of trouble differentiating between the concepts of 'genetic drift' vs 'genetic flow'. I have looked them up in my bio texts, but if somebody wouldn't mind explaining it, I would really appreciate it. thanks
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Postby Khaiy » Thu Mar 30, 2006 3:37 pm

Genetic drift is a description of the statistical tendency of alleles to vary over time. The basic reasoning is that due to the randomness involved in passing alleles onto successive generations, the frequency of an allele that doesn't have a strong positive or negative effect will vary from generation to generation.

Genetic flow is a description of the alleles that enter a population due to migration.

Did that clear it up for you?
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Postby bionewbie » Thu Mar 30, 2006 4:21 pm

yes it did clear up a little bit ... so how does natural selection fit into all of this?
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Postby MrMistery » Thu Mar 30, 2006 5:20 pm

natural selection basically decides which animals reproduce.
In a small population genetic drift is more important for telling which animals reproduce and which don't. In a big one, it's natural selection.
Natural selection interferes with genetic flow in a way that it keeps the best alleles, so it keeps the imigrants or not. Usually it does from what i know..
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Postby Khaiy » Fri Mar 31, 2006 5:31 pm

The way my biology professor once described it was that when traits make an organism more or less viable in its environment, then natural selection will drive evolution by increasing the number of viable individuals and reducing the number of nonviable ones.

But when a random event (that has nothing to do with viability) affects a population's reproduction, then genetic drift will be the result. The larger the population is, the better it can absorb genetic drift according to the laws of probability.

If you imagine a patch of flowers by itself, with natural selection operating, then they will reproduce according to whatever flowers have the most beneficial alleles. But if a dog suddenly ran through the patch and ripped up a lot of the flowers, then any rare alleles that the ripped up flowers had would be removed from the population, regardless of their contribution to the flower's reproductive viability.

After something like that happens (I mean in a situation where genetic drift will have a great impact), there will be less diversity in that population, which will change the way that natural selection operates on it. Fewer alleles mean fewer chances to respond successfully to environmental changes, which can endanger the population over time.
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Postby Nithin » Fri Apr 07, 2006 6:49 am

Genetic drift is the term used in population genetics to refer to the statistical drift over time of allele frequencies in a finite population due to random sampling effects in the formation of successive generations. In a narrower sense, genetic drift refers to the expected population dynamics of neutral alleles (those defined as having no positive or negative impact on fitness), which are predicted to eventually become fixed at zero or 100% frequency in the absence of other mechanisms affecting allele distributions.

Your question regarding selection
By definition, genetic drift has no preferred direction. A neutral allele may be expected to increase or decrease in any given generation with equal probability. Given sufficiently long time, however, the mathematics of genetic drift (cf. random walk) predict the allele will either die out or be present in 100% of the population, after which time there is no random variation in the associated gene. In this regard, genetic drift tends to sweep gene variants out of a population over time, such that all members of a species would eventually be homozygous for this gene. Genetic drift is opposed in this regard by genetic mutation which introduces novel variants into the population according to its own random processes.

Like selection, genetic drift acts on populations, altering the frequency of alleles (gene variations) and the predominance of traits. Drift is observed most strongly in small populations and results in changes that need not be adaptive.
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