Changes in the gene pool can occur due to various mechanisms. In 1989, a large oil spill occurred in Prince William Sound, Alaska, when the Exxon Valdez oil tanker ran aground. Approximately 11 million gallons of oil were spilled and spread 1,300 miles along the Alaskan coastline. The damage from the oil spill affected thousands of animals in the area, including killer whales, harbor seals, sea otters, fish, and sea birds. Which mechanism most likely affected the gene pools of the organism populations in the areas around the oil spill?
The oil spill caused a sudden, large reduction in the numbers of many local populations. When a population shrinks sharply by chance, some gene variants may become more or less common simply because the surviving individuals are a random sample; this is genetic drift. Mutation introduces new gene variants, while gene flow moves variants between populations, neither of which is the main mechanism described here.
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