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In a hypothetical situation, the Vermont State Park Service decides to build a pedestrian bridge over the Rock River in the town of Newfane. Upon completion, the pedestrian bridge will enable the passage of two closely related populations of mud lizards that had previously existed either on the eastern or the western side of the river but had been unable to cross the river.

Just before completion of the bridge and then fifteen years after the completion of the bridge, graduate students from the University of Vermont collected twenty-five lizards from each side of the river, took blood samples, and determined the frequencies of alleles that were unique to the two types of mud lizards. The results of their sampling are shown in the graphs below.

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The data from the students' investigation show which of the following?


The completion of the bridge allowed for the formation of a hybrid zone between the Eastern and Western mud lizards.


The Eastern and Western mud lizards did not intermix despite the construction of the bridge.


Gene flow occurred from the Eastern mud lizard gene pool into the Western mud lizard pool.


The two mud lizard populations intermixed after the completion of the bridge, but they did not hybridize.

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