In population genetics, when does gene flow occur?

• A. When a population experiences a mutation rate high enough to immediately fix a new allele.
• B. When individuals (or their gametes) migrate between populations and successfully reproduce, transferring alleles.
• C. When mating occurs only among close relatives within a population (inbreeding).
• D. When allele frequencies change due to random sampling error in a small population (genetic drift).

Answer: (B)

Verified step by step guidance

1. Understand that gene flow refers to the movement of alleles between populations through migration and reproduction.
2. Recognize that gene flow occurs specifically when individuals or their gametes (such as pollen or sperm) move from one population to another and successfully reproduce, introducing new alleles into the recipient population.
3. Differentiate gene flow from other evolutionary mechanisms: mutation introduces new alleles within a population, inbreeding involves mating among relatives without allele movement between populations, and genetic drift is a random change in allele frequencies within a population.
4. Focus on the key aspect of gene flow being the transfer of alleles across population boundaries, which increases genetic similarity between populations.
5. Summarize that gene flow occurs when migration and successful reproduction lead to allele exchange between distinct populations.