Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

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What effect does natural selection have on population variation?

It increases genetic variation
It decreases genetic variation
It has no effect on genetic variation
It randomly affects variation

The correct answer is: It decreases genetic variation

Natural selection plays a significant role in shaping the genetic variation within a population by favoring certain traits over others based on their adaptive value in a specific environment. This process can lead to a decrease in genetic variation over time as advantageous traits become more common in the population while less advantageous traits may diminish or disappear altogether. When individuals with favorable traits survive and reproduce, they pass those traits on to their offspring, while individuals with less favorable traits may not survive to reproduce as successfully. This selection pressure can lead to a more homogenous population where the genetic diversity associated with the less favored traits is lost. Over generations, this results in a reduction of genetic variations, as seen in populations that undergo strong selective pressures or face environmental changes. In contrast, while other mechanisms such as mutation may introduce new variations, natural selection acts selectively to ensure that those variations that contribute to survival and reproduction are the ones that thrive, thereby decreasing the overall genetic variation in the population.