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, researchers collected ten antelope squirrels from both sides of the river, took blood samples, and collected frequencies of alleles unique to the two types of antelope squirrels (see the following graphs).
The data in the previous graphs 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. two-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.
The non-adaptive mechanisms of evolutionary change are:
a. migration (gene flow), mutation, and genetic drift.
b. migration (gene flow), balancing selection, and genetic drift.
c. migration (gene flow), sexual selection, and genetic drift.
d. mutation, sexual selection, and genetic drift.
e. mutation, genetic drift, and heterozygote advantage.