Which statement accurately describes gene flow?

Gene flow refers to the transfer of genetic material, in the form of alleles, from one population to another. This process can occur through various means, such as migration, where individuals from one population move into another and interbreed, thereby introducing new genetic variation. This exchange can significantly impact the genetic diversity within populations and can influence evolutionary processes by making populations more genetically similar over time.

The other options presented focus on different concepts in population genetics and evolution. For instance, the first option mentions natural selection, which is a mechanism of evolution that involves differential survival and reproduction based on advantageous traits, rather than the movement of alleles. The third option discusses gene mutations, which are changes within the DNA sequence itself, but do not involve the movement of alleles between populations. Lastly, the fourth option refers to the movement of entire populations, which may be related to migration as well, but does not specifically capture the idea of genetic exchange that characterizes gene flow.

Thus, the correct statement that accurately describes gene flow is the movement of alleles between populations, as this encapsulates the essential mechanism of genetic exchange that affects population dynamics and evolutionary trajectories.