Answer:
C) Gene flow
Step-by-step explanation:
Gene flow refers to the movement of alleles between local populations. It results from the migration of individuals. Two adjacent populations can exhibit gene flow due to the mating between their individuals and can have significant evolutionary consequences as it does not allow the reproductive isolation of these populations. In the given example, the two mice populations are present on either side of a river. Mating between the mice of the two populations resulted in gene flow and maintained resemblance among their members.