One plant produced sesquiterpene, (E)‐β‐farnesene (EBF), has been considered a potential defense against aphids, since its emission by plants causes aphids to drop off the plant or depart from the feeding site. 

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Change in environmental condition is not necessary for natural selection.

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Genetic drift 

Genetic drift is an evolutionary force, in which allelic frequency change over generation Just by chance (sampling error). 

The deviations from the expected ratios are random, the direction of change is unpredictable.

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CAUSES OF GENETIC DRIFT

Genetic drift in a small population over multiple generations can significantly affect the composition of a population’s gene pool. 

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Founder effect

A few individuals form a population start a new population with a different allele frequency than the original population.

Sampling error can arise is through the founder effect, which results from the establishment of a population by a small number of individuals.

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Genetic bottleneck

Genetic drift arises is through a genetic bottleneck, which develops when a population undergoes a drastic reduction in size