What is a con of migration?

• A. It affects only a small region of the genome
• B. It changes allele frequencies slowly
• C. It is perfectly predictable
• D. You get the entire genome, migration is a one time event so you would need to use other forces to make further changes

Answer: (D)

Gene flow through migration tends to equalize genetic differences between populations by moving alleles from one group to another. That can be a drawback when each population is adapting to its own local environment, because the incoming alleles may be less suited to local conditions and disrupt locally favorable allele combinations. Migration affects many parts of the genome, not just a small region, since the individuals bringing new alleles carry the entire genome with them. If migration is sustained over generations, its effect accumulates, continually reshaping allele frequencies across the genome.

Another important point is that migration is rarely a one-time event. New migrants can keep entering populations over time, so gene flow persists and continuously influences genetic structure. Because of that ongoing influx, other evolutionary forces—like natural selection, mutation, and drift—must act in combination with migration to create further changes or maintain distinct populations.

In short, a key downside of migration is that it erodes local adaptation by homogenizing genetic differences across populations and spreading alleles broadly across the genome, and this process is typically ongoing rather than a single, isolated event.