genetic drift?

Asked by achalgoel | 18th Jan, 2010, 12:30: AM

Expert Answer:

Genetic drift refers to the random fluctuations in the frequency of the appearance of a gene in a small isolated population, presumably owing to chance rather than natural selection.

Genetic drift is a random statistical effect and can occur only in small, isolated populations in which the gene pool is small enough that chance events can change its makeup substantially. It is a stochastic effect that arises from the role of random sampling in the production of offspring.

The individual changes are most often small or gradual and genetic drift is most often slow. But in the long run it can constitute a large part of the changes in a gene pool. Genetic drift also often cause alleles to disappear completely. The changes due to genetic drift are not driven by environmental or adaptive pressures, and may be beneficial, neutral, or detrimental to reproductive success.  

Although genetic drift is a mechanism of evolution, it doesn’t work to produce adaptations.


Imagine there are both red worms and white worms in the same population. Let there be ten red worms and ten white worms with equal chances of surviving to reproduce. A tree falls on the swamp, killing eight worms; six white and two red. Then suppose two white worms and one red worm get sick and die. By chance, there are now seven red worms and only two white worms left. This is an example of genetic drift.

Genetic drift can also occur through a random sampling error. A sampling error occurs when a sample exhibits different results than the entire population would. For example, say there are fifty red worms and fifty white worms in a population, and scientists randomly select ten worms to observe. Because the sample is smaller, the alleles passed on in the group of ten may not even out as they would in a group of one hundred. Also, if the group contains more red worms than white, the presentation of alleles in the offspring will be skewed.

Answered by  | 20th Jan, 2010, 12:49: PM

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