Which statement best describes gene flow's effect on genetic variation within a population over time?

• A. It decreases the overall number of alleles
• B. It increases genetic variation within the population by introducing new alleles
• C. It has no effect on variation
• D. It prevents any changes in allele frequencies

Answer: (C)

Gene flow involves the movement of genes between populations through migration. When migrants bring new alleles into a population, they expand the local gene pool, increasing the number of alleles and often raising heterozygosity. Over time, this makes the population more genetically diverse. So the best description is that gene flow increases genetic variation within a population by introducing new alleles. The idea that it has no effect isn’t accurate because migrants can introduce alleles that were absent locally, changing allele frequencies. It also doesn’t prevent changes in allele frequencies; it tends to shift them toward the frequencies found in the donor population and, overall, increases variation rather than decreasing it.