The correct answer is gene flow.
Gene flow is also called gene migration. It is the movement of alleles or genes from one population to another through migration. Gene flow occurs due various kinds of events such as pollen grains are blown by winds to new location. In this question a mouse with curled whiskers migrates from one forest community to another. She mates with other mice in the new community. Through gametes during reproduction, the gene for curled whiskers passed to her offspring.