Which of the mechanisms below increases the amount of genetic variations in a population?

A, because it actually results in new genes being created through mutation

B is close, but I would say it spreads existing variation within the population, which is positive but only goes so far if there is not new material being introduced.

C and D are right out, they decrease the genetic variation of a population

Which of the mechanisms below increases the amount of genetic variations in a population?
==> A. Genetic drift
B. Gene flow
C. Bottleneck effect
D. Founder effect
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Genetic drift is a mechanism of evolution that acts in concert with natural selection to change the characteristics of species over time. It is a stochastic effect that arises from the role of random sampling in the production of offspring. Like selection, it acts on populations, altering the frequency of alleles and the predominance of traits amongst members of a population, and changing the diversity of the group. Drift is observed most strongly in small populations and results in changes that need not be adaptive.

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I hope this is helpful.