gen-define-genetic-drift-and-give-one-short-worked-example-8e1c

Define genetic drift and give one short worked example.

# Genetic Drift **Definition:** Genetic drift is the random change in allele frequencies in a population from one generation to the next due to chance events, particularly in small populations. Unlike natural selection, drift is non-adaptive and doesn't favor beneficial traits. ## Worked Example: The Bottleneck Effect **Scenario:** A population of 1,000 beetles has two color alleles: - Brown (B): frequency = 0.5 (500 beetles) - Green (G): frequency = 0.5 (500 beetles) A forest fire randomly kills most beetles, leaving only 10 survivors: - 7 brown beetles - 3 green beetles **Result:** - New frequency of B = 0.7 - New frequency of G = 0.3 The allele frequencies changed dramatically (0.5 → 0.7 for brown) not because brown was advantageous, but purely by chance. If the population rebuilds from these 10 survivors, green beetles may become increasingly rare or even disappear entirely through continued drift, despite having no survival disadvantage. This demonstrates how random sampling during a population bottleneck causes allele frequencies to shift unpredictably.