Question

Peromyscus polionotus is a species of mouse found in inland fields as well as on the Gulf and Atlantic coasts of the southeastern United States. Coastal populations of this species have lighter fur than inland populations, and coastal populations blend into a beach environment more easily than the field mice do. Scientists investigated changes in two genes, Agouti and Mc1r, that are involved in fur coloration in this species. The table shows data from this investigation.

Location Phenotype Agouti Gene Mc1r Gene
Gulf coast Lighter coat color Mutated No mutation
Atlantic coast Lighter coat color No mutation Mutated
Inland Darker coat color No mutation
No mutation
Source: Steiner et al., Molecular Biology and Evolution, 2009

Which evidence would BEST support the claim that the phenotypes of these populations of mice are a result of natural selection?
A
A mutation in the same gene led to the coastal populations having the same coat color.
B
An allele for light coat color is more common in the coastal populations than the inland population.
C
The genes that code for a light coat color have been lost from the inland population.
D
The coastal and inland populations all share the same alleles for coat color.

Answer 1

B

If natural selection favors lighter fur on beaches, alleles for light coat color should be more common in coastal populations than inland ones. That pattern (higher frequency where the trait is advantageous) is direct evidence of selection. The other choices either don't show a frequency difference (D), could result from drift or other processes (C), or describe a specific mutation pattern that isn't necessary to demonstrate selection (A).