Gene flow is

• A. Any movement of genes from one population to another, and is an important source of genetic variation
• B. A mutation that creates new alleles
• C. The movement of genes within a population across generations
• D. Selective mating within a population

Answer: (A)

Gene flow is the movement of genes between populations, usually through the migration of individuals or their gametes into a new population. When migrants bring their alleles into another group, those alleles become part of the local gene pool and can spread through the population over generations, increasing genetic variation and reducing differences between populations. This is why the statement about any movement of genes from one population to another being an important source of genetic variation fits best.

Other ideas describe different processes: a mutation creates new alleles within a population, not by moving genes between populations; the movement of genes within a population across generations refers to inheritance and changes in allele frequencies inside the same population rather than introduction from outside; selective mating within a population changes allele frequencies through mating preferences but doesn’t introduce new alleles from outside sources.