The Following Questions Refer to the Paragraph and Graphs Below

Multiple Choice

The following questions refer to the paragraph and graphs below.
In a hypothetical situation, the National Park Service, which administers Grand Canyon National Park in Arizona, builds a footbridge over the Colorado River at the bottom of the canyon. The footbridge permits interspersal of two closely related antelope squirrels. Previously, one type of squirrel had been restricted to the terrain south of the river, and the other type had been restricted to terrain on the north side of the river. Immediately before and ten years after the bridge's completion, ten antelope squirrels from both sides of the river were collected, blood samples were taken, and frequencies of alleles unique to the two types of antelope squirrels were determined (see graphs below) .


-The data in the graphs above indicate that

A) a hybrid zone was established after the completion of the bridge.
B) no interspersal of the two types of squirrel occurred after the completion of the bridge.
C) gene flow occurred from one type of squirrel into the gene pool of the other type of squirrel.
D) 2-way migration of squirrels occurred across the bridge, but without hybridization.
E) some northern squirrels migrated south, but no southern squirrels migrated north across the bridge.