5 Steps to a 5: AP Biology 2021 by Mark Anestis

Author:Mark Anestis
Language: eng
Format: epub
Publisher: McGraw-Hill Education
Published: 2021-11-15T00:00:00+00:00

Allele frequencies may change because of random factors or by natural selection. Let’s consider chance events first. Imagine a population of fish in a large pond that exhibits two alleles for fin length (short and long) and is isolated from other populations of the same species. One day, a tornado kills 50 percent of the fish population. Completely by chance, most of the fish killed possess the long-fin allele, and very few of these individuals are left in the population. In the next generation, there are many fewer fish with long fins because fewer long-finned fish were left to reproduce; that allele is much more poorly represented in the pond than it was in the original parent generation before the catastrophe. This is an example of genetic drift (Figure 11.1: a change in allele frequencies that is due to chance events. When drift dramatically reduces population size, we call it a bottleneck.

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