Bottleneck events reduce the genetic variation, certain alleles become fixed, thus helping populations that have nearly become extinct.
Bottleneck events reduce the size of the population and greatly reduce genetic variation. (D).
Bottleneck events are the reduction of a population due to various reasons such as drought, flood, and other environmental causes.
The bottleneck effect occurs when the size of a population is reduced for at least one generation.
As a result of a bottleneck, a population's genetic variation may be significantly decreased, leaving it more vulnerable to extinction if it is unable to adapt to climate changes or changes in resource availability.
Thus, option D is correct.
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