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).

-Speciation
A)occurs at such a slow pace that no one has ever observed the emergence of new species.
B)occurs only by the accumulation of genetic change over vast expanses of time.
C)must begin with the geographic isolation of a small, frontier population.
D)proceeds at a uniform tempo across all taxa.
E)can involve changes involving a single gene.

Question

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).

-Speciation
A)occurs at such a slow pace that no one has ever observed the emergence of new species. 
B)occurs only by the accumulation of genetic change over vast expanses of time. 
C)must begin with the geographic isolation of a small, frontier population. 
D)proceeds at a uniform tempo across all taxa. 
E)can involve changes involving a single gene.

Quizplus · Accepted Answer

The scenario described involves two closely related types of antelope squirrels that were previously geographically isolated on either side of the Colorado River. The footbridge allowed for interspersal and mating between the two types, leading to a change in allele frequencies over a span of ten years. This suggests that speciation may involve changes in gene frequencies, and not necessarily require vast expanses of time or complete geographic isolation. Therefore, choice E, which states that speciation can involve changes involving a single gene, is the best option.

The Following Questions Refer to the Paragraph and Graphs Below